[From the U.S. Government Printing Office, www.gpo.gov]













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  Aim:



                            Projected Impact  of
                Relative        Sea Level Rise on the
           National Flood Insurance Program


                                  property of   library





                                                     U.S. DEPARTMENT OF COMMERCE N0AA
                                                COASTAL SERVICES CENTER
                                                 2234 SOUTH HOBSON AVENUE
                                                 CHARLESTON ,  SC 29405-2413





                                         October     1991








                FEDERAL EMERGENCY MANAGEMENT AGENCY
                      FEDERAL INSURANCE ADMINISTRATION

                                                                                           77
 







                                                               PREFACE


              This study of the impact of relative sea level rise on the National Flood Insurance
              Program was authorized by Congress and signed into law on November 3, 1989.
              The requirements of this study as specified by the legislation are as follows:


              SEC. 5. Sea Level Rise Study


                       The Director of the Federal Emergency Management Agency shall co                               nduct
              a study to determine. the impact of relative sea level rise on the flood insurance
              rate maps. This study shall also project the economic losses associated with
              estimated sea level rise and aggregate such data for the United States as a whole
              and by region'. The Director shall report the results of this study to the Congress
              not later than one year after the date of enactment of this Act. Funds for such
              study shall be made available from amounts appropriated under section 1376(c) of
              the National Flood insurance Act of 1968.




























                        Discussions with Congress subsequent to the passage of the legislation clarified that the study by
              FEMA would pertain only to the impact of sea level rise on the National Flood Insurance Program.








                                          EXECUTIVE SUAIAMLRY


                   This report contains the findings and conclusions concerning how the
            National Flood Insurance Program (NFIP) would be impacted by a rise in relative
            sea level. Based on information recently released by the United Nations on the
            range in the magnitude of potential rise in sea level, two primary sea level rise
            scenarios were examined, a 1-foot and Moot increase by the year 2100. Under both
            scenarios, the elevation of the 100-year flood would be expected to increase by the
            amount of the change in sea level. The area inundated by the 100-year flood is
            estimated to increase from approximately 19,500 square miles to 23,000 square
            miles for the 1-foot scenario, and to 27,000 square miles for the Moot scenario. The
            region most significantly affected would be the Louisiana coast, where subsidence
            rates of 3 feet per century would compound the impact of global changes in sea
            level. Because of potential growth in population within the coastal areas of the
            Nation over the next century, as well as the expansion of the floodplain, the
            number of floodprone households is estimated to increase from approximately 2.7
            million to 5.7 million and 6.8 million by the year 2100 for the 1-foot and 3-foot
            scenarios, respectively.      Assuming current trends of development practice
            continue, the increase in the expected annual flood damage by the year 2100 for a
            representative NFIP insured property subject to sea level rise is estimated to
            increase by 36-58 percent for a 1-foot rise, and by 102-200 percent for a 3-foot rise in
            sea level.
                   Based on these findings, the aspects of flood insurance rate-making that
            already account for the possibility of increasing risk, and the tendency of new
            construction to be built more than one foot above the base flood elevation, the NFIP
            would not be significantly impacted under a 1-foot rise in sea level by the year 2100.
            For the high projection of a Moot rise, the incremental increase of the first foot
            would not be expected until the year 2050. The 60-year timeframe over which this
            gradual change occurs provides ample opportunity for the NFIP to consider
            alternative approaches to the loss control and insurance mechanisms of the NFIP
            and to implement those changes that are both effective and based on sound
            scientific evidence. Because of the present uncertainties in the projections of
            potential changes in sea level and the ability of the rating system to respond easily







            to a I-foot rise in sea level, there are no immediate program changes needed.
            However, the possibility existS 1F6r significant impacts in the long term; therefore,
            the Federal Emergency Manazement Agency (FEDAA) should:


                  0      continue to moninor progress in the scientific community regarding
                         projections of future changes in sea level and consider follow-on
                         stucties that proVide more detailed information on potential impacts
                         of sea level nse on -he NFIO;
                  0      in the near term.   consider the formulation and implementation of
                         measures that would reduce the imDact of relative rise in sea level
                         along the Louisiana coast; and
                  0      strengthen effortS to monitor development trends and incentives of
                         the Community 'Rating System that encourage measures which
                         mitigate the impacts of'sea level rise.







                          Acronyms and Abbreviations


        BFE                             Base Flood Elevation

        EPA                             Environmental Protection Agency

        FEMA                            Federal Emergency Management
                                        Agency

        FIA                             Federal Insurance Administration

        FIRM                            Flood Insurance Rate Map

        FP                              Floodplain

        IPCC                            Inter-Governmental Panel on
                                        Climate Change

        NASA                            National Aeronautics and Space
                                        Administration

        NFIP                            National Flood Insurance Program

        NGVD                            National Geodetic Vertical Datum of
                                        1929

        NOAA                            National Oceanic and Atmosphenc
                                        Administration


        NRC                             National Research Council

        P ('"I R                        Post Glacial Rebound

        SFHA                            Special Flood Hazard Area

        SWFL                            Stillwater Flood Level













                                     iv








                                 Conversion Table .. English to Metric Units




            Multiply                                                             To Obtain

            Inches(in)                                    25.4                   Millimeters (mm)
                                                           2.54                  Centimeters (cm)

            Feet (ft)                                      30.48                 Centimeters (cM-,)
                                                           0.3048                Meters (m)

            Miles (mi)                                     1.61                  Kilometers (km)

            Square Miles (mi2)                             2.59                  Square Kilometers (kM2)

            Temperature Change                             5/9                   Temperature Change
            [Degrees Fahrenheit (,oF)]                                           [Degrees Celsius (K)]


            To obtain absolute Fahrenheit (F) t-emperature readingsfrom Celsius (C)
            readings, use fo=ula: F          9/5      32

























                                                             v









                                        TABLE     OF CONTENTS


                                                                                         Page

            1.0          Summary                                                          1

                         1.1   Background                                                 1
                         1.2   Study Objectives and Approach                              2
                         1.3   Findings                                                   4
                         1.4   Conclusions and Recommendations                            7

              .0         Introduction                                                     10

                         2.1   Sea Level Rise in the United States                        11
                         2.2   Purpose of Study                                           19

            3.0          Physical Changes                                                 23

                         3.1   Methodology                                                23
                         3.2   Results                                                    39

            4.0          Demographics                                                     42

                         4.1   Methodology                                                43
                         4.2   Results                                                    46

            5.0          E-,o*nomic Implications for the NFIP                             50

                         5.1   Background                                                 50
                         5.2   Methodology                                                51
                         5.3   Impact on Insurance Premium Requirements                   57
                         5.4   Impact on Losses                                           64
                         5. 05 Program Impact                                             65
                         5.6   Study/Mapping Requirements                                 67



            References                                                                    68











                                                     vi








                                               LIST OF TABLES

                                                                                                Page

            Table 3.1            Value of Coefficient b for the Scenarios                       25
                                 Considered in this Report

            Table 3.2            Milestones for 3-Foot Sea Level Rise                           Z7
                                 Scenario Corresponding to Successive 1-Foot
                                 Increments of Rise

            Table 3.3            Milestones for 1- and 3-Foot Relative                          30
                                 Sea Level Rise Scenarios for Louisiana

            Table 3.4            Area Affected Due to a 1-Foot Rise in Sea Level                40
                                 by the Year 2100

            Table 3.5            Area Affected Due to a 31-Foot Rise in Sea Level               41
                                 by the Year 2100

            Table 4.1            Estimated Total Householdsin the Coastal                       47,
                                 Floodplain for the 0-, 1-, and 3-Foot Sea Level
                                 Rise Scenari o s by the Y. ear 2 100 (In Millions)

            Table 4.2            Estimated Number ofHouseholds by Region in the                 49
                                 Coastal Floodplain for -the 0-, 1-, an@ 3-foot Sea
                                 Level Rise Scenarios by -the Year 2100 (In Thousands)

                                         T
            Table 5.1A           Post-F.IRM Actuarial Increase in Average Premiums              57
                                 for Buildings Subject to Sea Level Rise Required
                                 to Maintain Actuarial Soundness


                                        T
            Table 5. 1B          Pre-FIRM Subsidized Increase in Average Premiums               EQ
                                 for Buildings Subject to Sea Level Rise Required
                                 to Maintain Current Subsidy Level














                                                         Vii









                                             LIST OF FIGURES


                                                                                           Pagge

            Figure 3.1          Eustatic Sea Level Rise for the 1- and                      26
                                3-Foot Sea Level Rise Scenarios

            Figure 3.2          Major Geomorphic Regions that are Representative            28
                                of the Range of Subsidence Rates in Coastal
                                Louisiana

            Figure 3.3          Schematic Diagram of the Effect of Sea                      34
                                Level Rise on the 100-Year Coastal
                                Floodplain

            Figure 3.4          Coastal Physiographic Regions of the United                 37
                                States Based on Morphological and Geologic
                                Variations

            Figure 4.1          Population as a Function of Time Based on                   45
                                Information Supplied by Woods & Poole, 1990

            Figure 5.1A         1990 Representative Pre-FIRM Distribution                   54
                                (V-Zone)

            Figure 5.1B         1990 Representative Pre-FIRM Distribution                   55
                                (A-Zone)

            Figure 5.2          1990 Representative Post-FIRM Distribution                  56

            Figure 5.3          1-Foot Sea Level Rise Scenario: V-Zone                      5S

            Figure 5.4          1-Foot Sea Level Rise Scenario: A-Zone                      59

            Figure 5.5          3-Foot Sea Level Rise Scenario: V-Zone                      60

            Figure 5.6          3-Foot Sea Level Rise Scenario: A-Zone                      61















                                                     Vill








                  PROJECTED MPACT OF RELATIVE SEA LEVEL RISE ON THE
                             NATIONAL FLOOD INSURANCE PROGRAM




            1.0 SUAMARY

            Ll     Background


                   The rise of global sea level over the past century has been documented by
            several investigators using tide gage measurements. At specific locations, the
            change in sea level relative to the land is dependent upon the effects of any local
            land subsidence or uplift. For areas experiencing a significant rate of uplift (such
            as portions of the Alaskan coastline), relative sea level has been decreasing, while
            for areas in which subsidence is taking place (such as port-Ions of Louisiana's
            coastline), relative sea level is Increasing at a more rapid rate than in other areas.
                   A                      th
                    .1though it is lknown - at mean sea -level fluctuates over long time periods,
            the exact causes of 'these natural changes are not well understood. It has been
            suggested by some that the recent rise of sea level is related to global warming (the
            greenhouse effect@ and that, as the atmosphere warms, the oceans will rise
            because of the melJting of ice masses and thermal expansion of the oceans. The
            magnitude of historical global warming,          its anthropogenic and/or natural
            origins, and its link to sea level rise are issues that are currently subject to
            intense scientific scrutiny. The potential magnitude of warming and the degree to
            which it would be delayed by the thermal inertia of the oceans are uncertain.
                                                                 A
            Also, the degree to which changes in precipitation affecting the ice caps and
            mountain glaciers might change the volume of water removed from the sea and
            stored is uncertain.
                   The atmosphere and ocean are complex systems, making long-term
            climate and sea level predictions extremely difficult. Numerical models of global
            climate change, although ever advancing, are still limited in their ability to
            accurately predict changes in the atmosphere and ocean over long (decadal or
            centennial) time scales. Even though these limitations exist, the most sound basis
            for predicting changes in this global system is the combination of numerical







             modeling and analyses of the available long-term environmental records (the past
             2-8 million years of the geologic record).
                    The above uncertainties have prompted investigators interested in
             quantifying the impacts of potential sea level rise to address a rancre of sea level
                                                                                     t@
             rise scenarios. These scenarios generally assume that the rate of sea level rise
             will accelerate with time and that a greater rate of rise will occur in the latter half
             of the next century.
                    A significant increase in relative sea level could cause extensive shoreline
             erosion and inundation. Higher relative sea level would elevate flood levels and
             therefore require alteration of the 100-year coastal floodplain delineated by the
             Federal Emergency Management Agency (FEMA). Flood events would impact
             more property and result in greater damage as sea level increased. This problem
             is exacerbated by the present trend towards increased concentration of population
             in coastal areas.


             1.2    Study Objectives and Approach
                 The primary objective of this study is to quantify the impacts of sea level rise on
             (1) the location and extent of the U.S. coastal floodplain, (2) the relationship
             between the elevation of insured properties and the 100-year base flood elevation
             (BFE), and (3) the economic structure of the National Flood Insurance Program
             (NFIP). The coastal floodplain area affected includes areas subject to increased
             erosion and submergence. In response to sea level rise, changes will occur in the
             extent of the coastal floodplain, in the portion of the coastal floodplain that is
                bject to flooding and modest wave action (A-Zone), and in the portion of the
             coastal floodplain subject to flooding and significant wave action (the velocity zone
             su


             or V-Zone). Areas affected by flooding (both coastal and riverine) are shown on
             Flood Insurance Rate Maps (FIRMs) published under the NFIP.
                    For this study, an average insurance risk was identified based on flood-
             depth distributions reflected in current flood insurance policies.            Different
             distributions were assigned to pre-FIRM and post-FIRM structure categories.
             For the purpose of this study, pre-FIRM structures were defined as structures
             built before 1980; post-FIRM structures are structures built after 1980.



                                                        2








                    Two sea level rise scenarios for the period 1990 to the year 2100 were
             examined in this study. Based on recent scientific investigations, the first
             scenario is a 1-foot rise in sea level by the year 2100. The second scenario is the
             high scenario of a Moot rise in sea level by the year 2100. Studies supporting these
             scenarios include the report entitled Scientific Assessment of Climate Change
             prepared for-the Intergovernmental Panel on Climate Change (IPCC) by Working
             Group No. 1 (IPCC, 1990). The IPCC was jointly established @y the World
             Meteorological Organization and the United Nations Environment Programme.
             For comparison purposes, a no-rise scenario is also cited in this report.
                    Accomplishing a study of this Scope and magnitude required that several
             assumptions be made. It is important to understand that these assumptions can
             significantly influence the quantitative results of this study.              The major
             assumptions are described below:
                    1.    Census data were used to est-    ablish population -#,,--,ends in each coastal
                          countv to the year 2010. Projectionsbe,7ond 2010 (-to the vear 2100) were
                          based on tilese 11.I-rencis. "Ihis a-puroach assumes a linear increase of
                          population over time and does noL account for development saturation
                                        %,                -ors which could signin-cantly affect the
                          that may oc ur or other fact
                          population trends adopted for this study, such as changes in
                          mortality rates, fertility rates, and social and recreational trends.
                    2.    Within each coastal county, the total households (based on population
                          estimates) were assumed to be uniformly distributed over the total
                          land area of the county. The number of households in the county's
                          floodplain was determined by multiplying the total number of
                          households by the ratio of floodplain area to total county land area.
                          This assumption was necessary because of the lack of quantifiable
                          information about the variation of the density of households in the
                          floodplain. This assumption could lead to either an overestimate or
                          underestimate of the number of floodplain households in each
                          county.
                    3.    This study assumes that no engineering solutions or land use/coastal
                          zone management practices are implemented over the study period


                                                        3







                          other than current practices related to elevation of structures.
                          Options that could substantially mitigate the impacts of sea level rise
                          in open coast areas include armoring of the shoreline (e.g.,
                          constructing seawalls, breakwaters, and dikes), beach
                          renourishment, and the adoption of setback reg-ulations. The effect of
                          thi's assumption is that the projections contained in this report will be
                          overestimated.
                   4.     The obsolescence of structures was not considered in this study.
                          Based on the expected life of a coastal structure, a certain fraction of
                          these structures will become obsolete each year and will be replaced
                          by new structures which will be in compliance with the current
                          NFIP regulations for construction at that time. Since obsolescence
                          has not been accounted for, the actual insurance risk may be
                          overestimated in this study.


             1.3   Findings
               The current total 100-year coastal floodplain area is approximately 19,500 square
             miles (50,500 square kilometers) for all coastal regions of the United States. Most
             of this area is contained in the coastal states from the Mid-Atlantic region to the
             Gulf of Mexico region. The west coast, Alaska, and Hawaii together account for
             no more than 5 percent of the total coastal floodplain area. The additional areas
             that may be affected by the 100-year flood are estimated to be approximately 2.200
             square miles (5,700 square kilometers) for the 1-foot scenario and 6,500 square
             miles (16,830 square kilometers) for the Moot scenario when subsidence in
             Louisiana is not taken into account. When subsidence in Louisiana is accounted
             for, these fig-ures become 3,400 square miles (8,800 square kilometers) and 7,700
             square miles (19,900 square kilometers), respectively.
                   The estimated total number of households in the coastal floodplain for the I-
             foot and 3-foot sea level rise scenarios for the year 2100 are shown in the following
             table.  The numbers in brackets reflect the case when subsidence in Louisiana is







                                                      4







               taken into account. For comparison purposes, expected results for a no-rise
               condition (i.e., 0-foot scenario) are also shown to indicate the influence of
               population estimates on the number of floodprone households.


                 TOTAL ESTIMATED HOUSEHOLDS IN THE COASTAL FLOODPLAIN
                                                             (IN MILLIONS)

                                              Current            0' Scenario          1'Scenario         3'1 Scenario
                                             Households                 2100            12100               -9100

               HOUSEHOLDS ENT
               A-ZONE                              2.4                  4. 05            5.0                5.9
                                                                        [4.61           [5-11               [6.11

               HOUSEHOLDSIN
               V-ZONE                              0.28                 0.010             0.61              0.73
                                                                        [0 -81
                                                                          .0             [0.641             [0.751

               TOTAL HOUSEHOLDS
               IN COASTAL
               FLOODPLAIN                                                                                     6
                                                                           .2j           [5.71              [6.81

                       A model       representing the shift4ng distribution of risk characteristics of
               NFIP business         was created to provide some insight into the relative changes in
               expected losses        and resulting premiums caused by an increasing flood risk over
               time. The analysis was limited to the consideration of the standard flood
               insurance coverage provided to buildings insurable under the NFIP and not the
               additional erosion benefits afforded by the Upton-Jones Amendment, which was
               enacted in 1988.
                       The Upton-Jones program and its associated benefits were not considered
               in this study for several reasons.                         Engineering solutions, coastal zone
               management practices, and other options discussed in Item 3 on page 3 would
               influence the vulnerability of structures and their eligibility for benefits under the
               Upton-Jones Amendment.                      Although these kinds of impacts have been
               investigated in some studies (National Research Council (NRC), 1987;
               Environmental Protection Agency (EPA), 1989), the effect of sea level rise on the
               Upton-Jones program cannot be determined without conducting a study that



                                                                        5








               specifically addresses this issue. Furthermore, even without the additional
               impacts of sea level rise, there are concerns about the pricing of Upton-Jones
               coverage and the lack of a companion erosion management program that make
               the long-term continuance of the present Upton-Jones program problematic.
               Since this study was undertaken, a bill has been introduced to repeal the Upton-
               Jones flood policy benefit and substitute a mitigation assistance program under
               which limited funding would be available for relocation of structures threatened
               by coastal erosion.
                      In assessing the potential impact of sea level rise, this study examines the
               sensitivity of the NFIP's rate structure to the changing conditions as an
               indication of the degree to which program changes would have to be made and of
               the criticality of the timeframe in which such changes might be needed. A rising
               sea level in combination with increasing population will not only increase losses,
               but also increase the number of policies and thus premium income available to
               pay losses. Therefore, the analysis focused on whether existing rate structures
                                                                                        Z@
               will be adequate to address the problem of maintaining an overall premium
               income level commensurate with the level of losses, and how premium charges
               should be distributed among the policyholders who have varying degrees of risk
               exposure. Because the program will be insuring a dwindling                 number of pre-
               FIRM buildinas over the course of 110 years, sea level rise is mainly an issue for
               post-FIRM construction. The following table shows the results of the analysis for
               this latter category of business.
                                             POST-FIRM ACTUARIAL
                                     INCREASE LNTAVERAGE PREMIUMS
                              FOR BUILDINGS SUBJECT TO SEA LEVEL RISE
                           REQUIRED TO MAINTAIN ACTUARIAL SOUNDNESS
                                             (Rates Per $100 Coverage)
                                      A-ZONE                              V-ZONE
                             Full Risk                            Full Risk
                             Premium Rate         Percent        Premium Rate         Percent
                             1990 2100             Change        1990 2100            Change


               1-Foot
               Rise          0.19    0.30           58%          0.66 0.90             36%


               3-Foot
               Rise          0.19    0.57         200%           0.66 1.33            102%


                                                            6









                   The percent change shown in this table reflects how the average full risk
            premium rates per $100 of coverage, and therefore the total premium income, for
            1)ost-FIRM T)olicies subject to sea level rise would have to increase in order to cover
            flood insurance losses. The relative change and magnitude of the rates indicate
            that there is ample flexibility in the NFIP rate structure to accommodate a 1-foot
            rise in sea level. A 3-foot rise may require that additional me@sures be taken to
            distribute premium burdens equitably and avoid undue cross subsidies.
                   In addition, the potential map revision and restudy requirements were
            considered. It is estimated that a total of 283 counties will be affected by increases
            in sea level. For these counties, approximately 5,050 FIRM panels will need to be
            revised as sea level rises. The cost of revising the affected map panels to account
                                            A         -imate ' to be $30,000,000. This cost would
            for each 140ot increase in sea level is est      (I L
            be spread over a 4- to 5-year period.


            1.4    Conclusions and Recommendations
                   There is a great deal of uncertainty 'In (-.he current projections of the rate of
            sea level nse. Moreover, the aspects of flood insurance rate-making that account
            for the possibility of increasing nsk, and the tendency of post-FUIRM construction
            to be built more than 1 foot above the BFE combine to eliminate any immediate
            threat from sea level rise to the NFIP's ability to insure against flood losses
            through a system of pricing that is fair and that protects the NFIP's financial
            soundness. There is no need for the NFIP to develop and enact measures now in
            response to the potential risks that would accompany increasing sea levels. As
            more information is collected over the next several decades, our ability to analyze
            past trends and our confidence in predictions will increase, allowing us to better
            assess both the magnitude of the problem and the most appropriate responses.
                   The high projection of a 3-foot increase by 2100 shows that a 1-foot increase
            would not be realized until 2050. This 60-year horizon provides ample time to
            consider alternative approaches and implement those that are both effective and
            based on sound scientific evidence.




                                                       7









                     For these reasons, the following technical and policy procedures are
              recommended:
                     1.    FEMA must continue to monitor progress made by the scientific
                           community in improving the reliability of projections of the potential
                           increase of relative sea level. A formal report should be prepared
                           beginning in 1995, and every five years thereafter, by the Federal
                           Insurance Administration (FIA) identifying the advances made in
                           the capability to predict potential changes in global sea level. In
                           addition, alternative fiscal and mitigation measures designed to
                           minimize the impact of future increases of sea level on the NTFIP
                           should be examined.
                     2.    Because of the more immediate threat and definitive trend of
                           subsidence along regions of the Gulf of Mexico coastline, especially
                           within and near Louisiana, FEMA must explore and consider
                           adoption and implementation of appropriate measures to mitigate
                           the effects of this increasing risk.        The process of identifying
                           appropriate mitigation measures and the data needed to support
                           these measures should include coordination with other Federal and
                           State aaencies involved with this problem.                The measures
                                                                                         -her coastal
                           implemented in these regions will serve as models for ot
                           areas when the broader issue of global change of sea level requires
                           directed action by the NFIP.
                     3.    In the near term, FEMA will increase its efforts to encourage,
                           through the NFIP's Community Rating System, voluntary adoption
                           and enforcement at the State and local level of mitigation measures,
                           such as BFE freeboard requirements and construction setbacks, that
                           take the potential for increases in relative sea level into account. In
                           addition to working at the State and local level, FEMA must also
                           continue its work with national building code organizations to reflect
                           appropriate risks associated with the possibility of rising sea levels.




                                                        8









                  4.     FEMA will continue, and strengthen, its monitoring of the trend of
                         development patterns related to zoning and density to ensure that as
                         trends change there is no degradation that would compromise
                         fundamental goals and objectives of the NFIP. Furthermore, a
                         concerted effort must be made to continue to monitor redevelopment
                         as structures reach the end of their useful life to ensure compliance
                         with minimum NFIP standards.
                  5.     TMDrovement of this study in the future will depend on the
                         availability of more complete and accurate data and on the ease of
                         manipulating these data. For example, the creation of digital
                         aatabases of topographic and demographic information would offer
                         the possibility of efficiently computing the physical impacts of sea
                         level rise. These tools would allowfor regional or county studies to be
                         T)erlormed with more detail and confidence. Also, FE2VIA could more
                         confidently make Drojections of potential flood losses.
                  6.     FEIMA may undertake in the future a broad-based study to gather
                         and collate shoreline erosion information on a national basis. The
                         results of this effort would permit very site-specific determinations of
                         potential land loss due to sea level rise and would link FEMIA's efforts
                         in this area with those of other Federal agencies, e.g., U.S. Geological
                         Survey (USGS) and the EPA. These data would be useful for the
                         judicious implementation of construction setbacks.
                  7.     FEMA should undertake joint studies with other Federal agencies
                         which are involved in the global warming/sea level rise issue, e.g.,
                         EPA, USGS, National Oceanic and Atmospheric Administration
                         (NOAA), National Aeronautics and Space Administration (NASA).
                         The capability of FE1VIA to provide flood loss figures is attractive to the
                         other agencies that are interested in quantifying the losses or
                         damages associated with sea level rise.






                                                     9








             2.0 rqrMODUCTION
                 A rise in sea level could potentially have a major impact on the coastal areas of
             the United States. Physical effects associated with higher sea level are the
             inundation of coastal lowlands, increased shoreline erosion, and loss of wetlands.
             The loss of wetlands will affect the hydrodynamics and therefore the flooding
             characteristics of tidal bays and rivers. Shoreline recession and submergence of
             dry land are direct responses to rising sea levels.
                    The most vulnerable areas are coastal wetlands. A 1-meter (3.3-foot) rise in
             sea level by the year 2100 could result in the loss of 25-80 percent of the United
             States coastal wetlands (Titus et al., 1989). The greatest losses are projected to be
             in Louisiana, where shoreline erosion and land loss rates are presently the
             highest in the country. Since wetlands act as buffers to the inland penetration of
             coastal flooding, the loss of these areas will increase the extent and severity of
 71          flooding in many areas.
                  An increase in the severity of coastal flooding due to sea level rise and a
             subsequent increase in shoreline erosion could present a potential hazard for
             coastal development. Research shows that a significant portion of the Nation's
             shorelines are currently eroding. Presently, over 70 percent of the world's
             coastlines are eroding (Bird, 1985). The Natio   nal Shoreline Study by the United
             States Army Corps of Engineers (1971) reported that 43 percent of the shorelines in
             the United States are experiencing erosion. Leatherman (1988) estimated that
             90 percent of the U.S. shoreline consi    sting of sandy beaches is eroding. The
             average erosion rate, i.e., shoreline retreat, along the Atlantic coast is 2.6 ft/yr
             (0.8 m/yr) (NRC, 1987). The Pacific coastline has localized areas of erosion. For
             example, San Diego and Los Angeles Counties have ongoing beach
             renourishment projects.       Erosion in California is episodic and fluctuates
             according to climatic cycles of storm activity (see, for example, the October 1989
             issue of Shore and Beach, Vol. 57, No. 4, which describes in detail the impacts of
             the January 1988 storm). However, the U.S. Pacific shoreline is considered to be
             relatively stable since the majority of the coastline is hard rock (NRC, 1987).
                    In the United States, shorelines are retreating because of both natural and
             man-induced causes. Some scientists suggest that there is a direct causal



                                                      10







            relationship between landward shoreline retreat and relative sea level rise, which
            results in the displacement of the'shoreline and, in some cases, barrier island
            submergence (Leatherman, 1983, 1988; Everts, 1985). An increase in sea level will
            result in higher surge elevations and consequently higher waves. The overall
            result will be an increase in damage to coastal structures as sea level rises and
            the severity of storm-induced flooding increases.
                Coastal structures are increasingly being thrlatened due to shoreline retreat.
            Along the Atlantic coast, residential and commercial buildings and erosion
            control structures are damaged or destroyed each year by moderate northeasters
            and tropical storms. These structures will be affected to varying degrees by a rise
            in relative sea level. As shorelines retreat, larger wave heights are possible due to
            deeper nearshore waters, resulting in increased wave power and greater
            destructive force (NRC, 1987). Structures currently designed to withstand a 100-
            year storm event could be overtopped and/or destroyed. Similarly, some buildings
            that were built above the current BFE would be subject to flooding from such an

            event.
                Estimates of the magnitude of sea level rise vary widely within the scientific
            community. To assess the possible impacts associated with a rise in sea level, the
            change in sea level must be established. The following sections discuss the
            findings of various investigators and present both current and historical rates of
            change. While most experts agree that sea level is rising, opinions differ about the
            cause and magnitude of the rise. These issues are also briefly discussed in the
            following sections.


            2.1    Sea Level Rise in the United States
                   Scientists recognize and define two types of sea levels: eustatic and relative.
            Eustatic sea level refers to the global or worldwide height of sea levels. Changes
            in eustatic sea level result from a number of physical processes, primarily the
            melting of polar ice masses, thermal expansion of the oceans, and changes in
            oceanic volumes due to glacial displacement. Relative sea level refers. to the
            height of sea level as measured from the ground at a particular point or area on
            the earth's surface. Change in relative sea level usually results from the








               interaction of two different and essentially independent processes: 1) local change
               (uplift or subsidence) in the absolute elevation of the land mass and 2) change in
               the absolute elevation of the earth's ocean (eustatic changes).
                   Subsidence is caused by a localized downward displacement of the land mass
               and can usually be attributed to a number of factors, including 1) tectonic
               downwarping of the earth's crust, 2) consolidation and compaction of sediments,
               and 3) withdrawal of subsurface fluids. It is important to note that given fixed
               eustatic sea levels, subsidence alone could account for dramatic rates of shoreline
               retreat and increased coastal erosion. For example, in the Teche basin of
               Louisiana, subsidence rates average 1.11 cm/yr (0.44 in/yr) which accounts for
               more than 80 percent of the local relative sea level rise for this region (Ramsey
               and Penland, 1989).
                   Uplift of the land surface is primarily caused by 1) tectonic uplift due to the
               movements of the earth's ocean and/or continental plates and 2) isostatic rebound,
               that is, uplift of the continental crust due to the retreat of the glaciers that covered
               the northern portion of the United States (and Canada) during the end of the
               Pleistocene epoch, approximately 15,000 years ago. The southeast coast of Alaska
               is an area which has been experiencing uplift of the land mass. Here, the rate of
               relative sea level rise ranges from -2.2 to -17.3 mm/yr (-0.09 to -0.68 in/yr) (Gornitz
               and Kanciruk, 1989), where a negative sign indicates that relative sea level is
               decreasing.
                     The primary method of measuring rates of sea level rise is to compare
               historical and recent sea level data that have been collected from tide gages.
               Unfortunately, accurate long-term tide gage data are unevenly distributed
               spatially and temporally. For example, the majority of tide gage stations are
               located in the northern hemisphere, and the longest records are generally for
               areas in the North Atlantic.
                  Analysis of the tide gage data shows that the rates of relative sea level rise are
               unevenly distributed across the globe. For example along the southeast coast of
               Alaska, geologic uplift associated %&rith isostatic rebound is greater than eustatic
               sea level rise, thus the net result is a localized decrease in relative sea level.
               Conversely, in the Gulf of Mexico, the extraction of subsurface fluids has caused a



                                                         12







           decrease in the elevation of the land mass. This decrease, combined with eustatic
           sea level rise, results in a rapid rise in relative sea level.             Tide gage
           measurements reflect relative changes in sea level; thus to isolate eustatic
           changes, the effects of uplift and subsidence of the land surface must be removed
           from the data2.
                 Most scientists agree that eustatic sea level is rising. Prevailing theories
           attribute the rise to the combined effects of melting polar ice caps and thermal
           expansion of the oceans, processes that have been occurring since the glaciers
           retreated from the northern hemisphere during the end of the most recent Ice
           Age (Wisconsin Stage of the Pleistocene epoch), about 15,000 years ago. Prior to the
           decay of the Wisconsin Stage glaciation, sea level was approximately 400 feet lower
           than present. From 15,000 to about 6,000 years ago, eustatic sea level. rose, on
           average, 3.5 ft/century (1.1 m/century). During the.past 6,000 - 7,000 years,
           however, the rate of sea level rise has decelerated, and in the past century, global
           eustatic rise, based on historical tide gage data, has been estimated to range from
           1.1 to 3.0 mm/yr (0.04 to 0.12 in/yr) (Carter, 1988).
                 Douglas (1991) suggests that the wide discrepancies among estimates of
           regional trends of sea level rise are mostly due to the location of tide gage stations
           on convergent plate boundaries. The resulting contribution of vertical crustal
           movements due to post glacial rebound (PGR) can account for as much as 50
           percent of the observed relative sea level rise (Gornitz et al., 1990). Peltier and
           Tushingham (1989) examined tide gage records and estimated that global eustatic
           sea level rise is 2.4 mnL/yr (0.09 in/yr) by determining a correction value for PGR at
           each station. Using the same correction values for PGR established by Peltier and
           Tushingham (1989), Douglas estimated global eustatic sea level rise to be 1.8
           mm/yr (0.07 in/yr), which is comparable to Peltier and Tusliingham's estimate
           (Douglas, 1991). The difference was attributed by Douglas to be due to his
           exclusion of tide gage records located at convergent plate boundaries. This
           research demonstrates that a reliable estimate of sea level rise based on tide gage
           records can not be made without considering PGR (Douglas, 1991).




                 2Another factor that must be considered and compensated for is the unevenness of the surface of the
           ocean, caused by the effects of currents, winds, tides, and changes in atmospheric pressure.
                                                    13








                   Many scientists predict that the rate of rise will increase in the future due to
               elevated global temperatures caused by increased levels of greenhouse gases in
               the atmosphere. The major contributors to greenhouse warming are carbon
               dioxide (55 percent), chlorofluor.ocarbons (24 percent), methane (15 percent), and
               nitrous oxide (6 percent) (1PCC, 1990). The NRC (1983) estimated that there is a 75-
               percent probability that carbon dioxide concentrations will double by the year 2100.
               With an estimated temperature increase of 1.50 to 5.5o Celsius (C) (2.70 to 9.90
               Fahrenheit (F)) associated with an increase in greenhouse gases equivalent to a
               doubling Of C02, global mean sea level is expected to rise over the next century. It
               should be noted, however, that recent studies suggest that global warming due to
               .increased atmospheric concentrations of greenhouse gases may be overstated.
               For example, in a recent study, Lindzen (1990) analyzed time series for annually-
               averaged surface temperatures dating back to 1855. He found that there was no
               significant variation of global temperatures in excess of 1oC (1.8oF). According to
               his results, temperatures have been fairly stable during the past 135 years,
               suggesting that current models may overestimate global warming.                       A
               chronological review of recent scientific literature pertaining to global warming
               scenarios and corresponding sea levels shows the variability in estimates of
               projected sea level rise. For example:
                     0      Revelle (198  3) estimated that sea level could rise a total of 70
                            centimeters (2.3 feet) by the year 2085, with a 25 percent margin of
                            error indicated.
                     0      Hoffman et al. (1986), in an update to Hoffman et al. (1983), predicted
                            future sea level rise in the year 2100 to be within the range of 57 to 368
                            centimeters (1.9 to 12 feet).
                     0      Robin (1987) forecast a rise in sea level of 0.8 meter (2.6 feet), with a
                            range 0.2 to 1.6 meters (0.6 to 5.2 feet), by the year 2100.
                     0      A report issued by the NRC (1987) entitled Responding to Change in
                            Sea Level:- EnLyineerinL- Imi)lications included a discussion on
                            mechanisms affecting sea level. The NRC report summarized
                            earlier studies and concluded that a realistic estimate of sea level rise




                                                         14








                         associated with increased carbon dioxide concentrations is from 0.5
                         to 1.5 meters (1.6 to 4.9 feet).
                  0      MacCracken et al. (1989) used the oceanic heat transport model of
                         Frei et al. (1988) and estimated less than a 0.5- to 1-meter (1.6-to 3.3-
                         foot) rise in sea level by the year 2100.
                  0      Meier (1ï¿½90) reports that the current "best estimate" of sea level rise
                         is 0.3 meter (1 foot) by the year 2050, with a "high estimate" of as
                         much as 0.7 meter (2.3 feet) by the   iyear 2050, and a "low estimate"

                         near zero.
                  0      The NRC (1990) summarized recent findings on the effect of
                         atmospheric temperature change on the world's oceans. They
                         concluded that "one hundred years from now, it is likely that sea level
                         will be 0.5 to 1 meter (1.6 to 3.3 feet) higher than it is at present."
                  0      A study prepared by the IPCC, entitled, Scientific Assessment o
                         Climate Change (IPCC, 1990), presented 1-foot, 2.2-foot, and 3.6-foot
                         scenarios as the low, best, and high estimates of sea level rise
                         expected by the year 2100. The IPCC was jointly established by the
                         World Meteorological Organization and the United Nations
                         Environment Programme in        1988 to assess scientific information
                         related to various components of the climate change issue. The
                         estimates cited above correspond to a "busines s-as- usual" scenario;
                         that is, it is assumed that no steps are taken to limit greenhouse gas
                         emissions. Other scenarios were considered in which progressively
                         increasing levels of controls reduce the growth of emissions. These
                         latter scenarios lead to smaller projections of the sea level rise than
                         the "business-as-usual" scenario.
                  Potential contributors to sea level rise include thermal expansion, the
           Alpine and Greenland glaciers, and the Antarctic Ice Sheet. It is controversial
           whether the contribution of the Antarctic Ice Sheet to sea level is negative or
           positive. There is, no conclusive evidence to date that shows this ice sheet has
           contributed to sea level rise over the past 100 years (IPCC, 1990). An increase in
           global temperatures could increase snowfall accumulation over the sheet,



                                                     15







              resulting in a negative contribution to sea level. On the other hand, increased
              temperatures might eventually cause an instability of the ice sheet with outflow of
              ice and meltwater into the ocean and a rise of sea level. Meier (1990) suggests that
              much of the meltwater from the polar ice caps will percolate and refreeze in the
              subfreezing snow. Furthermore, it is unlikely that any contribution from the ice
              shelves will have an appreciable impact on sea level by the year 2050, given the
              slow response of the ice shelves to slight changes in global temperature. There is
              some speculation that this outflow could become significant beyond the 110-year
              time frame addressed in this report (IPCC, 1990). However, there is great
              uncertainty on this issue. The IPCC (1990), in formulating its sea level rise
              scenarios, considered that even in the worst case (high scenario) there would be
              no contribution from Antarctica.
                     Because of the number of physical parameters involved, it is not possible to
              assign to the various sea level rise scenarios statistical confidence intervals in a
              strict sense. The l__PCC generated three projections -- best estimate, high, and low --
              based on an estimated range of uncertainty in each of the potential contributing
              factors and in the resulting global warming predictions.
                     If global temperatures increase, changes in climate could occur that would
              affect hurricane activity. There has been scientific speculation about the effect of
              global warming on the frequency, intensity, and tracks of hurricanes. Some
              scientists theorize that storm frequency and intensity may increase and storm
              tracks may be displaced farther to the north as global temperatures increase.
              According to the IPCC (1990), the ocean area having the critical temperature at
              which tropical storms are created (26oC/79oF) will increase as- global
              temperatures change. However, climate models to date give no indication
              whether the intensity and frequency of tropical storms will increase or decrease
              as the climate changes (IPCC, 1990). Mid-latitude storms may consequently
              weaken or change their tracks in response to warmer temperatures in the
              northern hemisphere. There is some evidence of a decrease in the irregularity of
              mid-latitude winter storm tracks based on model simulations (IPCC, 1990). These
              are research topics that are currently being investigated, and no firm conclusions
              are available. The effects of a change in climate on precipitation patterns and


                                                        16








            smaller scale disturbances are continuing to be researched. If these effects are
            proven to be significant, then there could be an appreciable impact on the
            characteristics of the 100-year floodplain delineated by FEMA. Because of the
            uncertainty in the current estimates of future storm patterns due to global
            warming, no attempt has been made to include these effects in this study.
                  Several, studies have examined the local effects of relative sea level rise
            based on projected increases in sea level. They include the following:
                  0      Kana et al. (1984) used a concept called "drown ed-valley" to project
                         new shorelines based on pre-existing contours for the City of
                         Charleston, South Carolina.
                  0      Leatherman (1984) projected current shoreline changes along
                         southeast Galveston Bay, Texas, for the years 2025 and 2075.
                  0      Gibbs (1984) performed an economic analysis of the effects of sea level
                         rise on the coastline of the City of Charleston, South Carolina, and the
                         City of Galveston, Texas. In this study, Gibbs examined anticipated
                         losses in dollars due to shoreline retreat and increased inundation.
                  0      Titus et al. (1991) projected the nationwide economic and
                         environmental impact of sea level rise to the year 2100 in terms of
                         inundation, shoreline retreat, and the costs of protecting developed
                         areas. Because of the high cost of applying detailed models to a large
                         number of sites, other factors, such as salt water intrusion and
                         increased flood hazards were not examined. Estimating anticipated
                         shoreline retreat and predicting the costs involved in holding back
                         the sea, however, were deemed feasible goals.


            Physical Effects of Relative Sea Level Rise
               A rise in sea level will result in shoreline recession. The EPA estimated that a
            1-meter (3.3 foot) rise in sea level would inundate 5,000 to 10,000 square miles
            (12,950 to 25,900 square kilometers) of dry land if attempts to stabilize the shoreline
            are not made (Titus et al., 1989). Shoreline erosion is a worldwide problem; over 70
            percent of the coastlines are undergoing significant erosion (Bird, 1985).
            Shoreline changes vary from the short-term erosion associated with individual


                                                      17







              storms to the longer-term effects of sea level rise. A significant rise in sea level
              establishes a setting in which increased erosion can occur.
                  Land loss and barrier island submergence result from a combination of factors
              associated with relative sea level rise. Barrier islands are dynamic features
              which will respond to rising sea levels in various ways. Traditionally, barrier
              islands were thought to migrate landward due to the formation of inlets and
              overwash processes during storm events, allowing sand to be transported from
              the beach to the bay shore. However, it has been suggested that in the short term,
              many coastal barriers are actually eroding on both the beach and bay sides and
              essentially are being forced to drown in place (Leatherman, 1983).
                  The NRC (1987) reports that shoreline erosion is probably responsible for about
              1 percent of the total annual marsh losses. Land losses in marsh areas due to sea
              level rise are more commonly a result of ponding, the rapid enlargement of
              interior ponds in marshes which occurs if there is a large increase in sea level.
              Shoreline stabilization, e.g., bulkheads and levees, will affect the amount of marsh
              area lost to sea level rise by limiting the marsh's natural ability to trap sediments
              and build above the rising sea level.
                  A change in the location and extent of coastal floodplain areas is another result
              of a rise in sea level. The change in floodplain area is dependent on slope,
              topography, use of protective coastal structures, and the magnitude of relative sea
              level rise. As the shoreline retreats in response to rising sea levels, additional
              areas of the floodplain will be submerged, and new areas will be periodically
              flooded. It is difficult to assess the extent of change in overall floodplain area due
              to a rise in sea level. However, the assumption can be made that an increase in
              relative sea level will result in new areas being subjected to the possibility of
              inundation by flood waters. Conversely, the resulting increase in shoreline
              erosion and submergence will cause a decrease in the area subject to flooding3.

                     The protective benefits offered by coastal structures will decline as sea level
              rises. Higher surge elevations and greater wave heights associated with an
              increase in sea level will result in an increase in destructive force and a decrease




                     3 FEMA defines flooding to.be **a general and temporary condition of partial or complete inundation of
              normally dry land" (44 CFR, Part 59).
                                                        18








           in the protection provided by the structure. Seawalls and bulkheads designed to
           withstand present estimates of wave action associated with a 100-year storm could
           be overtopped during storms of lesser magnitude, which could result in structural
           failure.
                  Seawalls and bulkheads, which are often -used to stabilize eroding
           shorelines and other areas vulnerable to wave attack, are usually not built to
           account for a significant short-term rise inisea level. The NRC (1987) suggests two
           ways that sea level rise could be incorporated in the design of coastal structures.
           Seawalls, bulkheads, and groins could be designed to accommodate the
           anticipated rise in sea level within the design life of the structure. Another
           method would be to upgrade the structure as sea level changes. Based on current
           estimates of sea level rise over the next century, structures with a design life of
           less than 50 years need not account for anticipated sea level rise (NRC, 1987). For
           a period of less than 50 years, modest increases in sea level based on current rates
           would amount to only a few inches and would therefore have little effect on most
           coastal structures.
                  A secondary effect associated with sea level rise is an increase in coastal
           flooding due to the potential inundation of drainage systems beyond design
           capacity. Titus et al. (1987) examined the cost of constructing coastal drainage
           systems to accommodate a potential rise in sea level versus the retrofit cost of
           modifying existing structures -if sea level rises. Their research indicates that
           retrofit costs depend on the type and design life of the existing structure, which
           varies from location to location, as well as on the overall change in sea level.


           2.2 Purpose of Study
           The purpose of this study is to assess the implications of sea level rise (both
           physical and economic) on the NFIP. To accomplish this goal, analyses were
           performed to estimate changes over time in floodplain location and extent, and
           population density. In addition to these analyses, this study applied          relevant
           results obtained from previous studies (N-RC, 1987; EPA, 1989; IPCC, 1990) to help
           evaluate the overall impact of sea level rise on the NFIP. A nationwide
           assessment such as this study cannot incorporate detailed information on           site-



                                                     19






                specific topography and different types of floodprone structures. However, general
                trends can be used to assess the potential impact on the NFIR
                     The task of predicting changes in relative sea level is a complex problem
                involving local, regional, and global factors. Undoubtedly, this complexity has led
                to the wide range of predictions concerning sea level change. Sea level rise during
                the next century will have a number of potential impacts on the NFIP. An
                evaluation of the effects includes consideration of flood risk assessment and flood
                insurance implications. The primary goals of the NFIP are the reduction of
                future flood losses and the transference of the costs of flood loss from the general
                taxpayer to those who choose to occupy floodplain areas. In support of NFIP goals,
                FEMA identifies flood risks and maps floodprone areas.
                       The primary strategy adopted by the NFIP for reducing flood losses to new
                construction in identified floodprone areas is requiring, at a minimum, elevating
                and/or flood-proofing of new structures to the elevation of the flood that has a 1-
                percent probability of being equaled or exceeded in any given year, which is
                referred to as the 100-year (or base) flood. Likewise, the NPIP utilizes the
                difference between the 100-year flood level (BFE) and the elevation of the lowest
                floor of a structure as the principal risk parameter upon which to base the flood
                insurance premium for the structure. In simple terms, a rise in relative sea level
                impacts the NFIP by increasing BFEs, thus increasing flood hazards beyond those
                expected at the time of construction and subjecting a larger number of structures
                to inundation during the 100-year flood. In addition to altering the flood-depth
                distribution of structures, sea level rise will result in greater inland penetration of
                flood waters and wave action and increased erosion. Therefore, this study focuses
                on the impact of relative sea level rise on the NFIP, including FIRMs, the change
                in actuarial risk, and the fiscal soundness of the program.
                      The potential effects of sea level rise on the Great Lakes region were not
                considered in this study. The easternmost Great Lake, Lake Ontario, has an
                elevation of approximately 247 feet above mean sea level, and therefore is unlikely
                to experience any sea level rise effects propagating upstream from the ocean.
                Furthermore, the more interior lakes are s        eparated from Lake Ontario by
                Niagara Falls and a series of manmade locks, thereby reducing the likelihood of


                                                          2D








            changes in lake levels due to some of these effects. Changes in Great Lakes levels
            are related to precipitation patterns, variable winds, the construction of various
            navigation facilities, and the re- configuration of adjacent terrain (e.g., storm
            sewers, clearing of forests) (Ramey 1952; Harris 1981). Smith (1991) indicates that
            lake levels could drop as water use increases in response to higher air
            temperatures. If global warming occurs, precipitation patterns over the Great
            Lakes Basin could be altered, althoughl it is premature to say in which direction
            the change would occur, i.e., the net effect of changing precipitation/evaporation
            patterns is uncertain. In the future, it is expected that scientists will be able to
            more accurately determine the contribution of each component of sea level rise.


            Impact on the NFIP
                In a study to determine the impact of increases in relative sea level on the
            NFIP, it is necessary to first establish assumptions concerning the potential
            increase in sea level over a specific time period. Several studies of the potential
            increase in sea level have reflected the uncertainty in predictive capability by
            reporting on various possible scenarios of increase over the next 110 years. The
            same approach was adopted for this NFIP impact study. The scenarios analyzed
            include a low level (1-foot rise by the year 2100) and an upper level (3-foot rise by
            the year 2100). The upper level scenario corresponds roughly to the 100-centimeter
            (3.3-foot) rise assumed by the EPA (Titus et al., 1989) in its report to Congress on
            The Potential Effects of Global Climate Chanize on the United States. Based on
            recent scientific investigations by the IPCC (1990), the upper end of a reasonable
            range of values is approximately a Moot rise in sea level by the year 2100. The
            IPCC report was the primary basis for the selection of the 1- and Moot scenarios.
            The first component of this study is an evaluation of the effects of sea level rise on
            the flood risk assessment aspects of the NFIP, including:
                   1.    Impact on base flood elevations
                   2.    Impact on the location and extent of the coastal floodplain







                                                      21









                     3.     Numbers of existing and future structures impacted
                     4.     Anticipated frequency and associated cost of study
                            and mapping updates
                    The second component of the study deals with the costs of transferring risk
              through the insurance mechanism and how changing risk conditions affect the
              ability to equitably distribute the costs. The aspects addressed include the
              following:
                     1.     Economic impacts of current FIA policies of using present (as
                            opposed to future) risk conditions for determining flood insurance
                            premiums. That is, how will the costs of flood losses increase under
                            the "present conditions" policy in an environment where actual risk
                            is increasing due to sea level rise, and how will this affect the fiscal
                            integrity of the NFIEP?
                     2.     Estimation of the increase in the number of floodprone structures
                            that will exist within the Special Flood Hazard Area (SFHA). This
                            topic deals with the increase in the number of floodprone structures
                            and changes in expected annual losses under the program.
                     3.     The sensitivity of the NFIP's rate structure to the changing
                            conditions as an indication of the degree to which program changes
                            would have to be made and of the criticality of the timeframe in
                            which such changes might be needed.
















                                                       22






 :L










           3.0 PHYSICAL CHANGES
                  The following key assumptions were used in the computation of the
           physical changes associated with sea level rise (more detailed descriptions of
           these assumptions are contained in the following section):
                  1.    The change in the 100-year stillwater flood level (SWFL) is equal to
                        the rise in sea level.
                  a     A single value of ï¿½WFL is used to represent each county. Even
                        though the SWFL usually varies throughout a county, a weighted-
                        average value was estimated for each county.
                  3.    The additional area affected by sea level rise is controlled by the ratio
                        of the sea level rise to the SWFL (i.e., the additional area is equal to
                        this ratio multiplied by the current floodplain area).
                  4.    The A-Zone and V-Zone proportions of the coastal floodplain do not
                        change as sea level rises.
                  These assumptions are believed to be reasonable approximations of the
           physical impacts that would accompany an increase in sea level, particularly on a
           nationwide basis.


           3.1 Methodology
                  This section describes the sequence of steps that lead to the quantification of
           impacts. The major components of the computational sequence are the changes
           in the floodprone area and the corresponding change in the number and flood-
           depth distribution of properties subject to flood hazards.
                  Current estimates of sea level rise cover ranges of 17 centimeters (0.56 foot)
           to 26 centimeters (0.85 foot) by the year 2050 (Commonwealth Secretariat, 1989),
           and 15 centimeters (0.49 foot) to 50 centimeters (1.64 feet) by 2050 UPCC, 1990). The
           IPCC estimates are based on current projections of greenhouse gas emission
           rates if no remedial reductions are instituted in the future (i.e., "business-as-
           usual"). Other scenarios that involve a reduction in these rates in the future
           result in lower sea level rise projections. A 1-foot rise of sea level by 2050
           corresponds to the NRC 1-meter (approximately 3-foot) scenario for the year 2100.
           Based on the projected rate of increase of greenhouse gas emissions, the IPCC


                                                     23







                projections for the year 2100 are (1) low scenario     31 centimeters (1 foot), (2) "best
                estimate" scenario -- 66 centimeters (2.2 feet); and (3) high scenario -- 110
                centimeters (3.6 feet). These estimates would decrease for scenarios under which
                greenhouse gas emissions are lower than for the business-as-usual scenario. A
                lowering of the rate of greenhouse gas emissions could be achieved by a variety of
                mitigation measures.      If emissions over the next century are controlled, global
                mean temperature increases are estimated to range from OJoC (0.18oF) to 0.2oC
                (0.36oF) per decade. These values are lower than the "business- as-usual " best
                estimate scenario of 0.3oC (0.45oF) per decade (with an uncertainty range of 0.2oC
                to 0.5oC (0.36oF to 0.9oF) per decade). Sea level rise best estimate predictions
                associated with three reduced levels of emission controls are 34 centimeters (1.12
                feet), 40 centimeters (1.31 feet), and 47 centimeters (1.54 feet) by the end of the next
                century UPCC, 1990). For this study, a 3-foot rise in sea level by the year 2100 was
                chosen as a median value between the high estimate and best estimate cited by the
                IPCC under the business-as-usual scenario.
                       For the purpose of this study, a "l-foot increase" criterion has been selected
                to judge when a restudy and FIRM revision would be appropriate. In other words,
                when the SWFL computed for a community has increased by 1 foot, it is assumed
                that a restudy and revision of the flood maps will be initiated. This criterion was
                also used to identify the discrete points in time at which computations of revised
                floodplain areas and floodprone structures would be undertaken. For the sea level
                rise scenarios evaluated in this study (the 1- and 3-foot rises by the year 2100), the 1-
                foot increments of change will appear at different times. For example, the first 1-
                foot change will be realized earlier for the 3-foot scenario than for the 1-foot
                scenario. For the 1-foot scenario, the first (and only) 1-foot change will not occur
                until the year 2100. For the 3-foot scenario, there are three increments over which
                a 1-foot change will occur.
                   It is generally agreed that the rate of sea level rise will increase with time, i.e.,
                a plot of sea level versus time would be a curve whose steepness increases with







                                                          24







                projections for the year 2100 are (1) low scenario -- 31 centimeters (1 foot), (2) "best
                estimate" scenario -- 66 centimeters (2.2 feet); and (3) high scenario -- 110
                centimeters (3.6 feet). These estimates would decrease for scenarios under which
                greenhouse gas emissions are lower than for the business-as-usual scenario. A
                lowering of the rate of greenhouse gas emissions could be achieved by a variety of
                mitigation measures. If emissions over the next century are controlled, global
                mean temperature increases are estimated to range from OJoC (0.18oF) to 0.2oC
                (0.36oF) per decade. These values are lower than the "business- as-usual" best
                estimate scenario of 0.3oC (0.45oF) per decade (with an uncertainty range of 0.2oC
                to 0.5oC (0.36oF to 0.9oF) per decade). Sea level rise best estimate predictions
                associated with three reduced levels of emission controls are 34 centimeters (1.12
                feet), 40 centimeters (1.31 feet), and 47 centimeters (1.54 feet) by the end of the next
                century (IPCC, 1990). For this study, a 3-foot rise in sea level by the year 2100 was
                chosen as a median value between the high estimate and best estimate cited by the
                IPCC under the business-as-usual scenario.
                      For the purpose of this study, a "l-foot increase" criterion has been selected
                to judge when a restudy and FIRM revision would be appropriate. In other words,
                when the SWFL computed for a community has increased by 1 foot, it is assumed
                that a restudy and revision of the flood maps will be initiated. This criterion was
                also used to identify the discrete points in time at which computations of revised
                floodplain areas and floodprone structures would be undertaken. For the sea level
                rise scenarios evaluated in this study (the I- and 3-foot rises by the year 2100), the 1-
                foot increments of change will appear at different times. For example, the first 1-
                foot change will be realized earlier for the 3-foot scenario than for the 1-foot
                scenario. For the 1-foot scenario, the first (and only) 1-foot change will not occur
                until the year 2100. For the 3-foot scenario, there are three increments over which
                a 1-foot change will occur.
                   It is generally agreed that the rate of sea level rise will increase with time, i.e.,
                a plot of sea level versus time would be a curve whose steepness increases with







                                                          24








            time. A formula for this curve has been proposed (NRC, 1987). In metric units,
            the equation is
                         T W = (0.0012 + AV1000) t + bt2

            where        T =    total relative sea level -rise (meters)
                         t =    time (years)
                         M =    subsidence (+) or uplift W in millimeters/year
                         b =    coefficleAt whose value is chosen to satisfy the requirement
                                that T (wqth M=O) assumes the correct (pre-assigned) eustatic
                                sea level rise value at some t

                  The first term on the right-hand side of the equation (.0012t) contains the
            estimated eustatic sea level rise rate over the past century, .00 12 m/yr or 0. 12 meter
            over 100 years. If this equation is cast in terms of English units, the equation
            becomes

                         T W = (.0039 + M) t + bt2
            where the eustatic sea level rise rate over the previous century is .0039 ft/yr, M has
            units of ft/yr, and b assumes the values presented in Table 3.1 for the 1- and Moot
            scenarios:



                  TABLE 3.1 VALUE OF COEFFICIENT b FOR THE SCENARIOS
                                    CONSIDERED IN THIS REPORT


                         Eustatic Component by Year 2100 (ft)       b (ft/_vr2)

                                       1                            0.000047
                                       3                            0.000212


               A plot of this equation is shown in Figure 3.1.      The computational milestones
            for the Moot eustatic sea level rise scenario are given in Table 3.2 (the years have
            been rounded off to the nearest decade).










                                                      25







                                     EUSTATIC SEA LEVEL RISE THROUGH 2100

                                                                     T(t) = (.0039)t + W
                                                                                                                                         5





                                                                         LEGEND

                                 4-                     1 -FT SLR                       + 3-FT SLR                                     -4





                      C)
                                 3-                                                                                                    -3
                      w
                      cr)



                      Uj

                      Uj


                      Uj         2-                                                                                                      2
                      C/)





                      cr)










                                 0                                                                                                        0
                                     T

                                 1990                                             2050                    2080             2100

                                                                                  YEAR


                                    Figure 3-17Eustatic sea level rise for the  I - and 3-foot sea level rise scenarios
  J @1











               TABLE 3.2 MILESTONES FOR 3-FOOT SEA LEVEL RISE SCENARIO
               CORRESPONDING TO SUCCESSWE 1-FOOT INCREMENTS OF RISE


                                                             3-foot Scenario,
                                 Sea Level Rise (ft)         Milestone Years


                                         1                   2050 [601*
                                         2                   2080 [901
                                         3                   2100 [1101




                      Number in brackets is number of years counted from 1990.


                These milestone years have been computed with M (subsidence or uplift) set to
            zero, so that the eustatic component controls the result. The inclusion of
            subsidence or uplift will, respectively, accelerate or delay the milestones. The
            factors that contribute to M have been discussed in Section 2.1. Subsidence is most
            dramatic in the Louisiana area, although there are appreciable subsidence rates
            along the entire east and Gulf of Mexico coasts. Subsidence rates in Louisiana
            vary spatially due to differential compaction and varying thicknesses in the
            Holocene layers (Penland et al., 1989). Shown in Figure 3.2 are three Louisiana
            basins representing the range of subsidence rates in coastal Louisiana. The
            region with the highest subsidence rate is the Teche basin, with a rate of 1.11
            cm./yr to 1.65 cm/yr (0.44 in/yr to 0.65 in/yr). These estimates are considered high
            because of the influence on tide gage records of flooding from the Atchafalaya
            River. The rate of subsidence for the Terrebone delta plain is about 1.18 cm/yr (0.46
            in/yr). The lowest estimates are for the Pontchartrain basin, where subsidence
            rates are estimated to be 0.10 cm/yr to 0.31 cni/yr (0.04 in/yr to 0.12 in/yr). An
            estimate of 0.9 cm/yr (0.35 in/yr) is quoted in the NRC (1987) study, which reports a





                                                       Z7







          LOUISIANA


























                                                                        ..............
                                              Ba on oug      0
                                                                                           New Orleans

                                                                                . . ....... .....


                                                                         ........ .......... ...........
                                                              .... ... .. ....
                                                             .......... ....


                                                              ............ .......
                                                                                ............
                                                             ..............
                                                                                    --v,,




                                                                  ...       . ......

                                                                           ..................
                                                                              .. ...........
                                                                           .. .. ..........
                                               Eugene Island
                                                               ............
                                                               .......... . .
                                                                  ....         .......
                                                                                   Grand
                 Teche Basin                                                       Isle
                 Terrebone Delta Plain
                 Pontchartrain Basin






                   Figure 3.2 Major geomorphic regions of coastal Louisiana used
                              to determine a representative subsidence rate for
                              the Louisiana area (redrawn from Penland et al. 1989).







            local subsidence rate of 0.89 cm/yr (0-35 in/yr) for Grand Isle, Louisiana. This
            subsidence rate was adopted as a representative rate in Louisiana for the purpose
            of this study.
                   Uplift (or rebound) is prominent in Alaska and, to a much lesser degree,
            along portions of the west coast. The rates for subsidence and uplift are
            approximately 0.35 in/yr (0.9 cm/yr) (Louisiana) and 0.14 in/yr (1.7 cm/yr) (Alaska),
            respectively. It is difficult to define an average rate of subsidence for the United
            States as a whole. Some regions of the United States are experiencing uplift and
            will balance the effects of subsidence to some degree, and some of the causes of
            subsidence (e.g., subsidence due to sediment compaction, and subsidence due to
            withdrawal of oil, gas, and water) can be expected to become less important in the
            future. Excluding Louisiana and portions of east Texas, a national average
            subsidence rate of 1 mm/yr (0.04 in/yr) or 10 cm/century (4 in/century) is a
            reasonable estimate. If this small but appreciable contribution of subsidence is
            neglected, the results in Table 3.2 can be considered representative of relative sea
            level rise for the United States as a whole, with the exception of Louisiana and
            Alaska.
                   For Louisiana, the presence of subsidence means that a relative rise of sea
            level of 1 foot will occur earlier than indicated in Table 3.2, which accounts for only
            the eustatic component of sea level rise. Conversely, for Alaska, the 1-foot rise will
            occur later than the year 2100. The milestone years for Louisiana for the 1- and 3-
            foot scenarios shown in Table 3.3 are based on the assumption that the rates of
            subsidence given above are constant (the years have been rounded off to the
            nearest half-decade or decade). In addition to the combined effect of subsidence
            and eustatic sea level rise, Table 3.3 also shows the impact of subsidence alone (no
            eustatic component).











                                                      29






                    TABLE 3.3 MILESTONES FOR I- AND 3'FOOT RELATIVE
                         SEA LEVEL RISE SCENARIOS FOR LOUISIANA


                                  1-foot Scenario      Moot Scenario
                                  (Subsidence +         (Subsidence +
           Relative Sea Level        Eustatic)            Eustatic)          Subsidence Only
            Rise (ft)            Milestone Years       Milestone Years       Milestone Years

               1                     2020                  2015                     2025

               2                                           2040                     2055

               3                                           2055                     2090


                  Table 3.3 shows that when subsidence is accounted for in Louisiana, the 1-
           foot increments of sea level rise occur much sooner than when subsidence is
           discounted, e.g., for the Moot scenario, the first 1-foot increase occurs in 2015
           rather than 2050. Calculations of relative sea level rise were carried out to the
           year 2100. The combined effect of subsidence and eustatic sea level changes were
           considered, which resulted in 4-foot and 6-foot total rises of sea level in Louisiana
           by the year 2100 for the 1-foot and Moot eustatic scenarios, respectively.
                 The problem of relative sea level rise is more immediate in Louisiana than
           in other parts of the country because of subsidence. Therefore, special attention to
           the situation in Louisiana is warranted in the near term. Detailed studies that
           define the magnitude of changes in sea level at specific locations throughout the
           Louisiana area and the implementation of mitigation procedures are appropriate.


           Selection of Areas for Study
               In a report on population change, NOAA used political, physical, and cultural
           criteria to identify "coastal" counties. Inland counties whose activities might
           influence the environmental [email protected] of the coast were also designated as coastal
           (Culliton et al., 1990). The coastal counties identified by NOAA were used as a
           guide in selecting areas (counties) for this study. This information was used to
           include counties with nearshore areas inundated by short-term rising water
           levels associated with oceanic phenomena (hurricane surge, extratropical


                                                    30







             11northeaster" storm surge, tsunamis). A total of 283 counties were included in
             this study. Of this total, 51 counties were located on the west coast, 65 on the Gulf
             coast, and 167 on the east coast.


             Computations of Chanizes in Coastal SFHAs
                    A reasonable working assumption is that an increase in sea level produces
             an equal increase in the FEMA regulatory SWFL, e.g., a 1-foot rise in sea level
             translates into a 1-foot increase in SWFL. The linear superposition of sea level
             rise and SVY'FL neglects some of the possible second-order dynamic interactions
             such as the effect of the increased water depth due to sea level rise on storm surge.
             'This assumption does avoid complications associated with regional differences in
             the dynamic components that make up the SWFL, e.g., hurricane surge on the
             east coast versus tsunamis on the west coast. The impact of sea level rise on the
             BFE in the high-velocity V-Zone wou      Id be greater than the impact on the BFE in
             the SWFL because the V-Zone incorporates the effect of wave heights.
             Accompanying a 1-foot increase in SVTFL would be a corresponding change in
             BFE (stillwater plus wave contribution) of as much as 1.55 times the change of
             SVY'FL, or 1.55 feet.
                 In tidally-affected rivers, the effects of sea level rise will propagate upstream.
             The extent of the propagation is determined primarily by the slope of the riverbed
             or slope of the riverine water surface. In other words, if there is a 1-foot sea level
             rise, a river that connects with the ocean or large embayment will not necessarily
             experience a 1-foot increase in elevation over its entire length. The upstream limit
             ofthe rise is a function of the "steepness" of the river or, equivalently, the absolute
             elevation of the river at any point along its length. The 100-year return interval
             event may propagate farther upstream than the sea level rise by itself. Therefore,
             for the case of storm surge in the presence of sea level rise, there will be
             potentially three distinct dynamic areas: (1) from the ocean to a point upstream
             where the sea level rise tails off, the combined effect of surge and sea level rise will
             be approximately additive, (2) from this point to some location farther upstream,
             t e surge, previously'augmented by the presence of the sea level rise, will be




                                                        31








            progressively less influenced by this rise, and (3) near the upstream terminus of
            the surge, there will be no effect due to the rise.
                This study did not attempt to exactly define the character of the sea level rise in
            upstream (upriver) areas. This would have required site-specific hydraulic
            calculations. In upstream areas, the absolute water- surface elevation (with
            respect to the National Geodetic Vertical Datum (NGVD), for example)
            corresponding to the 100-year SIATFL will tend to be higher than the flood elevation
            at the mouth of the river. According to the formula (cited below) adopted for this
            study for estimating changes in the 100-year floodplain, a larger value for SWFL
            results in a smaller change in the floodplain area as sea level rises. In the
            formula, the areal change is proportional to the ratio of sea level rise to the S,ATL.
            With SWFL increasing in the upstream direction, computed floodplain changes
            due to sea level rise will become progressively smaller. Therefore, the exact
            determination of the sea level rise component in these upstream areas is not
            considered crucial to the present calculations.
                A second assumption relates the above adjusted SWFL to the resultant change
            in the coastal floodplain area. The fractional increase in SWFL due to relative sea
            level rise is assumed to be matched by the same fractional increase in coastal
            floodplain. The fractional change in SWF     L is simply the ratio of the sea level rise
            to the present SWFL. The formula for the change in the floodplain is:

                                 Sea Level Rise
                                                   x (Current Coastal FP Area)
                                    SWFL

            where FP stands for floodplain.
                  For a coastal area whose land relief can be characterized by a single
            topographic slope, the above relationship holds exactly. The size of the coastal
            floodplain is a function of the topography; a steep slope would result in smaller
            changes in the SFHA, and a flat slope would result in larger changes. In the case
            of more realistic variable topography, the floodplain may be underestimated or
            overestimated using this formula. If a relatively flat area that is inundated by the
            100-year flood connects inland with a more steeply-sloping region, a rise in sea
            level may cause minimal additional flooding during the 100-year event.


                                                      32







             Conversely, flooding that is initially confined to a steep nearshore region that
             connects to a flat inland region may, with the addition of sea level rise, overtop the
             steep segment and spread widely over the flatter area.                In these two
             circumstances, the use of the prop  osed formula would, respectively, overestimate
             and underestimate the change in the floodplain. The calculations performed for
             this study were conducted on a countywide basis and then integrated to provide
             regional and national statistics. With this approach, it is expected that, overall,
             errors would tend to balance rather than accumulate.
                  For each county, the following steps preceded       the floodplain calculations
             described above:
                   1.     A single, countywide SWFL for coastal flooding, representative of the
                          county as a whole, was estimated for each coastal county. The
                          estimated SWFL was a weighted-average value chosen to reflect the
                          flooding impact of the individual stillwaters within the county. The
                          estimate was made to the nearest whole foot.
                   2.     Similarly, an estimate of a single SWFL, representative of the
                          designated V-Zones within each county, was made.
                   3.     An estimate was made of the total coastal SFHA within each county.
                          Only land areas were considered in this estimation.
                   4.     The fraction of coastal SFHA that is designated V-Zone was
                          estimated.



             Land Lost Due to Submergence and Erosion
                   Shoreline erosion and submergence (inundation) of coastal areas because of
             sea level rise are two processes that remove land area from the 100-year
             floodplain. However, sea level rise also adds land to the floodplain by increasing
             flood levels. These opposing tendencies are shown schematically in Figure 3.3.
             The net change in the size of the coastal floodplain should be approximately zero.
             It should be noted that in developed areas where land values are high (e.g. Miami
             Beach, Florida; Ocean City, Maryland; Atlantic City, New Jersey), shoreline
             protection measures are likely to be initiated. These include beach nourishment
             projects, and the construction of groins, levees, and seawalls (although many



                                                      33













                                                        Current 100-Year                    Addition to Floodplain
                                                        Coastal Floodplain                  Due to Sea Level Rise




                                              Submerged and Eroded
                                                   Area Due to
                                                  Sea Level Ris










       2100 1 00-Year Stillwater

       1990 1 00-Year Stillwater


               Sea Level (2100)
               Sea Level (11990)               000
                                            000

                                                                     Eroded Profile





                                        Figure 3.3-Schematic diagram of the effect of sea level rise
                                                     on the 1 00-year coastal floodplain







             states prohibit the use of "hard structures," which tend to reduce the usable beach
             area).    Such measures will diminish the amount of land lost due to sea level rise,
             as well as the additional land subject to flooding. These circumstances could
             result in a significant overestimate of the total losses (both physical and
             economical) reported in this -study.
                  Shoreline erosion is a complex process that has many causes, e.g., sea level
             rise, storm activity, local alongshore sediment transport patterns, the influence of
             coastal structures. As erosion proceeds, floodplain land that was formerly
             habitable is lost. Floodprone households in these erosion zones will eventually
             become a total loss unless they are relocated, or other measures are taken to
             protect them (e.g., shore protection structures).
                    Erosion rates apply to the recent past and therefore are associated with the
             recent rate of sea level rise.       Under the sea level rise scenarios described
             previously, the rate of sea level rise is assumed to gradually accelerate. It can be
             expected that there will be a concurrent increase in the rate of erosion. An
             approximation proposed by Leatherman (1985) assumes a direct correlation
             between the amount of shoreline retreat in the historical record and the rate of
             rise (feet per year) of sea level. For future years, the change in the erosion rate of
             the shoreline is equated to the change"in the rate of rise of sea level.
                    Shoreline erosion is usually identified by measuring the change in the
             lateral position of a shoreline. For a rising sea level, part of this change in
             shoreline position is due to the effect of submergence, i.e., the erosion estimate will
             reflect the impact of submergence. Submergence occurs in all tidally affected
             portions of a county in contrast to erosion which occurs principally for shorelines
             with wave exposure. The EPA (Titus et al., 1989) has estimated that a 1-meter (3.3-
             foot) rise of sea level will submerge 5,000-10,000. square miles of dry land. In this
             study (see Section 3.2), the additional floodplain area created by a Moot rise of sea
             level is estimated to be 6,500 square miles when subsidence in Louisiana is not
             taken into account and 7,700 square miles when this subsidence is included.
             Although these numbers are derived with different parameters and
             methodologies, their comparable magnitudes add support to the conclusion that




                                                        35








            there will be no net change in the size of the coastal floodplain area due to sea level
            rise, since the addition of floodplain area will be balanced by the land lost through
            submergence.


            Coastal Physiographic Regions
                The coastline of the United States was divided into a series of physiographic
            regions to develop both a regional and national           summary of the physical
            consequences of sea level rise. Regional divisions of the coastal United States were
            previously done by Lin (1980), the NRC (1987), and Armentano et al. (1988). Each
            analysis was based on a combination of physical and economic factors. A
            simplified version of the classification by the NRC (1987) was used to develop 11
            coastal regions for the continental United States, including Alaska and Hawaii
            (Figure 3.4). The regional divisions are based on variations in coastal
            morphodynamics and geologic history. For simplicity, regions consist of one or
            more whole states (i.e., no partitioning within a state), despite some regional
            variation within a state. The one exception is the state of Florida, where there is a
            large physical variation between the barrier islands along the Atlantic coast, the
            coral reefs of the Florida Keys, and the barrier islands along the Panhandle. As a
            result, the state was divided into two regions to account for the different
            morphological conditions between the Atlantic and Gulf coasts. The Florida Keys
            form a geological break between the Atlantic and Gulf coast barriers. For the
            purpose of this study, the Florida Keys were included in the Atlantic coast region.
                 Region 1, the New England area, extends from New York to Maine. The
            glaciated coast is composed of a series of coastal barriers characterized by spit
            growth across deep embayments. The mainland is interspersed with hilly
            lowlands and gentle slopes with some higher areas which form cliffs near the
            shoreline.
               Region 2, the Mid-Atlantic area, includes New Jersey, Pennsylvania, Delaware,
            the Delmarva peninsula (eastern shore) and the western shoreline of the
            Chesapeake Bay, Virginia, and North Carolina. This region is characterized by





                                                     36















                        REGION 9
                        Columbian                                                                                COASTAL PHYSIOGRAPHIC REGIFIONS
                        Oregon
                        Washington                                                                                             OF THE UNITED STATES


                                                                                                                                                                                                                            REGI
                                                                                                                                                                                                                            Now t

                                                                                                                                                                                                                            Maine
                                                                                                                                                                                                                            New
                                                                                                                                                                                                                            Mass
                                                                                                                                                                                                                            Rhod
                                                                                                                                                                                                                            Conn
                                                                                                                                                                                                                            Now























                                                                                                                                                                                                                    ................. ...
                                                                                                                                                                                                                    .................. ...
                                                                                                                                                                                                                     .................
                                      REGION 8

                                      California
                                                                                                                                                                                                                  . .. ...................
                                                                                                                                                                                                                  . . ............


                                                                                                                                                                                                                   4        ......

                                                                                                                                                                                                                        .... .. ....
                                                                                                                                                                                                                    . .. ...........



                                                                             40                                                                                                                          REGION 5
                                                                                                                                                                   f                                     Gulf Coast Florida
                                                                                                                                                                           REGION 6
                                                                                                                                                                                                         Western Florida
                                                                                                                                                                           Deltak Coast
                                                                           REGION I I
                                                                                                                                                                                                         Alabama
                                                                                                                     REGION 7
                                                     ........                                                                                                               Lousiana
                                                                            Hawaiian Islands                                                                                                             Mississippi
                                                                                                                     Texas




                                          REGION 10

                                           Alaska


                                                         Figure 3.4-Coastal physiographic regions of the United States based on morphological and geologic vari



/
           low-lying, moderately developed coastal barrier islands and marsh filled
           embayments. The western shoreline of the Chesapeake Bay primarily consists of
           low sandy shorelines, and low cliffs in some areas.
               Region 3 is the mesotidal coast of South Carolina and Georgia. This area is
           characterized by short, stubby barrier islands with marsh-filled lagoons. Because
           of the topography, the larger tidal range and the coarser sediments in this area,
           these islands are considered relatively more stable than the barriers of the Mid-
           Atlantic and Gulf coasts (NRC, 1987).
                The Atlantic coast of Florida, Region 4, is dominated by highly urbanized
           barrier islands backed by narrow lagoons. The low-lying islands of the Florida
           Keys, formed on coral reefs and limestone, are also included in this region. The
           Gulf coast of Florida, Region 5, is made up of the western shoreline of the Florida
           peninsula, the Florida Panhandle, Alabama, and Mississippi. This region is
           characterized by a continuous series of barrier islands and extensive marshes
           and swamps.
               The deltaic coast of Louisiana, Region 6, extends from the Chandeleur Islands
           to Isle Dernieres. The islands are mostly wetlands made up of fine-grained
           deltaic deposits.
                Region 7, the Texas barrier islands, is similar to the Mid-Atlantic barrier
           island group. The microtidal islands are generally wide and are backed by
           shallow lagoons and extensive wetlands. These barriers, however, have a stable
           sand source; therefore, shoreline erosion is not as critical as in other areas (NRC,
           1987).
                The Pacific coastline varies considerably among California, Oregon, and
           Washington. The coastline of California alternates between a continuous narrow
           beach along southern California, to rocky headlands and high cliffs from north of
           Point Conception to the Columbia River, Oregon. Washington is mostly flat-sloped
           beaches, with limited wetland areas. Despite regional variation within California,
           the northern and southern portions of the state were grouped together as Region 8
           for simplicity. Oregon and Washington make up the Columbian area, or Region 9.
               The Alaskan coastline comprises fjords, rocky islands, permafrost lowlands,
           and low barriers and spits. The entire Alaskan coast makes up Region 10.


                                                   38
           e







                The Hawaiian Islands, Region 11, are mostly volcanic rock, with sandy beaches
            produced by wave-action on the volcanic rock and coral reefs. The extensive coral
            reefs, which dominate the nearshore waters, create an abrupt change in slope.
                   Because of the modest impact of sea level rise in Alaska and Hawaii, these
            regions have been combined, for reporting purposes, with the Columbian and
            California regions, respectively.


            3.2 Results
                          The additional land area affected by a rise in sea level was estimated
            for the continental United States, Alaska, and Hawaii for the two scenarios used
            in this report. A schematic of the physical changes associated with a rise in sea
            level is shown in Figure 3.3. The additional area affected was calculated based on
            the methodology described in Section 3. 1.
                   Regional and national changes in land area for the year 2100, based on l-
            and Moot rises in sea level, are shown in Tables 3.4 and 3.5, respectively. The
            estimated national coastal floodplain area is 19,500 square miles. It is estimated
            that approximately 2,200 square miles will be added to the floodplain by a 1-foot
            rise in sea level and that approximately 6,500 additional square miles will be
            added by a Moot rise in sea level when subsidence in Louisiana is not taken into
            account. When this subsidence is accounted for, these figures become 3,400 and
            7,700 square miles, respectively. Tables 3.4 and 3.5 also partition the areas affected
            by sea level rise into A- and V-Zones.

















                                                      39













                         TABLE 3.4 AREA AFFECTED DUE TO A 1-FOOT RISE IN SEA LEVEL BY                                                   THE YEAR 2100





                                                                               FLOODPLAIN                  ADDITIONAL AREA AFFECTED DUE TO
                                          REGION                                    1990                             SEA LEVEL RISE
                                                                    A-ZONE       V_ZONE         TOTAL       A-ZONE        V-ZONE        TOTAL


                                 NEW ENGLAND                          992           180         1172             97           18           115

                                 MID-ATLANTIC                        4163           344         4507           545            44           589

                                 MESOTIDAL COAST                     1899           332         2231           155            28           183

                                 ATLANTIC COAST FLORIDA               846             42          888          ill              6          117

                                 GULF COAST FLORIDA                  2524           462         2986           267            49           316

                                 DELTAIC COAST                       2684          1010         3694           301           113           414
                                                                                                             [12031         [451]        [16541

                                 TEXAS                               .2328          822         3150           .231           82           313

                                 CALIFORNIA / HAWAII                  428             94         52 2            65           16             81

                                 COLUMBIAN / ALASKA                   296             49          345            34             6            40

                                 NATIONAL TOTAL                      16160         3335        19495           1806          362          2168
                                                                                                             [2708]         1700]        [34081


                              (UNITS ARE SQUARE MILES)
                              VALUES IN BRACKETS ARE BASED ON A SUBSIDENCE RATE OF 3 FEEPCENTURY FOR LOUISIANA












                              TABLE 3.5 AREA AFFECTED DUE TO A 3-FOOT RISE IN SEA LEVEL BY YEAR 2100




                                                                                     FLOODPLAIN                     ADDITIONAL AREA AFFECTED
                                                                                          1990                         DUE TO SEA LEVEL RISE
                                               REGION                       A-ZONE      VIONE          TOTAL       A-ZONE        V;ZONE       TOTAL

                                       NEW ENGLAND                           992          ISO          1172            291            53       344
                                       MID-ATLANTIC                         4163          344          4507           1633          134       1767
                                       MESOTIDAL COAST                      1899          332          2231            467            82       549
                                       ATLANTIC COAST FLORIDA                846            42            888          334            IF       351

                                       GULF COAST FLORIDA                   2524          462          2986            802          146        948

                                       DELTAIC COAST                        2684         1010          3694            903          339       1242
                                                                                                                     [18061         [6781     [24841
                                       TEXAS                                2328          822          3150            695          245        940
                                       CALIFORNIA / HAWAII                   428            94            522          194            48       242
                                       COLUMBIAN / ALASKA                    296           49             345          104            17       121

                                       NATIONAL TOTAL                       16160        3335          19495          5423          1081      6504
                                                                                                                     [63261       [14201      [7746]

                                    (UNITS ARE SQUARE MILES)
                                    VALUES IN BRACKETSS ARE BASED ON A SUBSIDENCE RATE OF 3 FEETICENTURY FOR LOUISIANA








          4.0 DEMOGRAPHICS
                 Demographic information was used to estimate the number of households
          that could be affected by sea level rise. This estimate is based on population
          growth projected for coastal areas.
                 A summary of assumptions adopted in developing the demographic
          information used for this study is provided below.. A more detailed discussion of
          these assumptions is presented in the following section.
                 1.     The standard demographic unit of households is used to characterize
                        floodplain occupancy and development. Data on numbers and types
                        of structures were not available for this study.
                 2.     The population, and therefore household, projections are based on
                        data from the Bureau of the Census,'with forecasts to the year 2010
                        conducted by Woods and Poole Economics, Inc. (Woods & Poole, 1990).
                        Projections to 2100 were based on the trends established for the period
                        prior to 2010. The result is a constant linear increase of population
                        with time.
                 3.     The distribution within each county is uniform, i.e., the density of
                        households at any point in time does not vary across the county. This
                        assumption was. necessary due to the lack of information that
                        quantifies the density of households in the floodplain. The impact of
                        this assumption depends on where the population cente     rs are located
                        within a county. If a center is principally within the floodplain (e.g.,
                        Miami, Florida), the assumption of uniform density may
                        underestimate the risk; conversely, if a center is principally outside
                        the floodplain (e.g., Jacksonville, Florida), then the risk may be
                        overstated.
                 4.     No consideration was given to the possibility of saturation of
                        development.     If saturation occurs, new households would be
                        displaced farther inland and therefore farther from the various
                        adverse effects associated with sea level rise.
                 5.     All floodplain was considered developable, e.g., public land was not
                        treated differently than privately owned land. Although areas


                                                    42






                                                                                                          A








                         defined under the Coastal Barrier Resources Act are delineated on
                         FIRMs, quantitative data are not readily available for these areas and
                         undevelopable land within the floodplain. Given the variable
                         distribution of publicly versus privately owned land in each county,
                         the effect  of this assumption could lead to an overestimate or
                         underestimate of the number of floodprone households in each
                         county.                          Ii
                   The overall effect of these assumptions is difficult to quantify and would
            require further investigation.


            4.1 Methodology
               As population increases, it @can be expected that households will be added to the
            floodplain. Similar to the prediction of potential sea level rise, projections of
            population change are uncertain, especially as the period for the projection
            inc reases. The Bureau of the Census was initially contacted for information on
            demographic changes. Subsequently, data on population trends and projections
            were obtained from Woods & Poole Economics, Inc. (Woods & Poole, 1990) for the
            period 1969 through 2010. These projections relied heavily on Census data and
            were extended through 2100 for purposes of this study.
               The population data consist of annual figures from 1969 through 2010 (41 years)
            for the entire United States, all states, and all counties. The data are derived from
            a model that considers both economics and Bureau of the Census mortality and
            fertility rates. County migration patterns are based on employment opportunities,
            with two exceptions: for population aged 65 and over and coll ege-/mili tary- aged
            population, migration patterns over the forecast period are based on historical
            migration and not economic conditions.
                  The reliability of the forecasts is limited by several circumstances. The
            analysis of historical data does not guarantee that some unforseen event(s) may
            occur in the future that does not follow the historical trend, e.g., a sudden
            economic change that occurs more rapidly or with more intensity than
            anticipated.    A second limitation results from doing forecasts for small
            geographic areas such as counties, i.e., the smaller the area the less reliable are



                                                     43








            the statistical models. Obviously, for the period 2010 to 2100, which is not covered
            by these population data, the limitations cited here are even greater.
                The Woods & Poole population figures through 2010 were used directly in this
            study. Figures beyond 2010 have been estimated by examining the trend prior to
            2010 and extrapolating that trend linearly to the terminal year 2100. The trend in
            the sub-interval 2000 to 2010 is adopted for the period 2010 to 2100. In general, this
            choice would be expected to lead to a lower projected rate of population increase for
            2010-2100 than for the period prior to 2010. A plateauing or saturation of the
            population in the second period seems intuitively reasonable and would prevent
            an explosive or unrealistic growth in population by 2100. However, the population
            trend, shown in Figure 4.1 for 1969-2010, is essentially linear and constant, which
            means that the adopted trend for 2010-2100 is also constant, i.e., there is no
            saturation predicted.
                 With the methodology established for calculating incremental changes in
            floodplain area and population (and, by further transformation, the number of
            households), the impacts of the two sea level rise scenarios can be evaluated for
            each milestone year (years corresponding to successive 1-foot increments of sea
            level rise). The population data were used to provide the total number of
            households given the number of persons per household specific to each county as
            reported by the Bureau of the Census. The Bureau of the Census number of
            households, which includes rental properties meant for occupancy, was selected
            to be the most representative characterization of development. Changes in
            population are matched by proportional changes in households.
                  A key assumption adopted in this study is that the population density for
            each county is uniform, i.e., a single population density applies to all parts of the
            county. Given this assumption and knowing the land area of the county, the area
            of the SFHA that is subject to coastal flooding, and the percentage of coastal SFHA
            that is V-Zone, the number of floodprone households partitioned into A- and V-
            Zones can be determined.









                                                     44







                                        NATIONWIDE COASTAL COUNTY POPULATION TOTAL


                                        130




                                        120
                                 cg)
                             z 0
                             0 CT     ,
                                1 6     110 -




                             Z   (D     100
                             0   C:
                                 0

                                  -0
                                 (D
                                  -0
                                 C        90
                             CL
                             02
                             CL


                                         80 -




                                          70

                                             1969                     1980                   1990                   2000                   2010


                                                                                         YEAR


                                              Figure 4.1 - Population as a function of time based on information supplied by Woods & Poole, 1990











           4.2 Results
                  The number of households affected by sea level rise is directly related to the
           physical changes described in Section 3.0. The number of households added due to
           growth in population is calculated just prior to imposing each successive 1-foot
           rise in sea level. The growth calculation is based on the coastal floodplain at the
           previous milestone year and the change in population from that milestone year to
           the current milestone year. Households added due to the expansion of the
           floodplain are calculated just after imposing a 1-foot rise in sea level. The
           expansion calculation is based on the increased area due to a 1-foot rise in sea
           level and the total population at the milestone year. The number of households
           lost due to erosion and submergence was not determined, because of the
           uncertainties involved in this calculation. These uncertainties include the density
           of households in the nearshore areas affected by erosion and submergence and
           the effects of mitigation actions such as coastal management (setbacks) and
           engineering solutions (protective structures, beach renourishment). These
           actions could appreciably alter the makeup of the nearshore households from that
           assumed in this report. These types of responses could not be considered in this
           type of study.
                  The current number of pre-FIRM households in the coastal floodplain is
           estimated to be 2.4 million. The total number of households (pre- and post-FIRM)
           in the current (1990) coastal floodplain is estimated to be 2.7 million. The total
           number of households projected to be in the coastal floodplain by the year 2100 for
           the 1- and 3-foot scenarios is shown in Table 4.1. A 0-foot scenario is also shown
           for comparison and considers only the addition of households due to growth in
           population. The total number of households of 5.6 and 6.6 million by the year 2100
           for the 1- and 3-foot rise scenarios, respectively, reflects both expansion of the
           floodplain and growth due to population increases. These estimates assume no
           subsidence in Louisiana.       If subsidence is    accounted for, the number of
           households become 5.7 and 6.8 million, respectively. The increase of floodplain
           households is strongly influenced by the growth in population, which accounts for
           90 percent and 76 percent of the households added to the floodplain for the 1- and 3-



                                                    46









                                     TABLE 4.1 ESTIMATED TOTAL HOUSEHOLDS IN THE COASTAL
                                                          FLOODPLAIN FOR THE 0-1 1-9 AND 3-FOOT SEA LEVEL RISE
                                                          SCENARIOS BY THE YEAR 2100 (IN MILLIONS)



                                                                            1990
                                                                      FLOODIPLAIN               O'SCENARIO               I'SCENARIO                TSCENARIO
                                                                     HOUSEHOLDS                       2100                     2100                      2100



                                           HOUSEHOLDS                        2.4                       4.5                      5.0                       5.9
                                           IN A-ZONE                                                  [4.61                    [5.11                     [6.11


                                           HOUSEHOLDS                        0.3                      0.55                     0.61                      0.73
                                           IN V-ZONE                                                  [0.58]                   [0.641                    [0.7A


                                           TOTAL
                                           HOUSEHOLDS                        2.7                       5.1                      5.6                       6.6
                                           IN COASTAL       2                                         [5.2]                    [5.71                     [6.81
                                           FLOODIPLAIN




                                                 This scenario Is provided to Illustrate the Increase In households due to population growth only
                                             2 Includes 2.4 million pre-FIRM households


                                                 Values in brackets are based on a subsidence rate of 3'/century for Louisianna







           foot rise scenarios, respectively. Table 4.2 shows a regional breakdown of the total
           number of households projected to be in the coastal floodplain by the year 2100 for
           the 0-, 1-, and 3- foot scenarios.











































                                                    48,







                            TABLE 4.2 ESTIMATED NUMBER OF HOUSEHOLDS BY REGION IN THE COASTAL
                                                  FLOODPLAIN FOR THE 0-1 1-@ AND 3-FOOT SEA LEVEL RISE
                                                  SCENARIOS BY THE YEAR 2100 (IN THOUSANDS)



                                                                              1990                         0* SCENARIO                       VSCENARIO                         3'SCENARIO
                                                                        FLOODPLAIN                         FLOODPLAIN                        FLOODPLAIN                        FLOODPLAIN
                           REGION                                        HOUSEHOLDS                        HOUSEHOLDS                        HOUSEHOLDS                        HOUSEHOLDS
                                                                                                                2100                              2100                              2100
                                                                    A-ZONE V-ZONE                      A-ZONE V-ZONE                      A-ZONE V-ZONE                     A-ZONE V-ZONE

                          NEW ENGLAND                                 868               54               1,306               98            1,432             108             1,677             126
                          MID-ATLANTIC                                591               33                 937               69            1,042              76              1,256               92

                          MESOTIDAL COAST                             107               18                 193               33             .209              36               239                41

                          ATLANTIC COAST FLORIDA                      135                 4                368               11              419              13               509                16

                          GULF COAST FLORIDA                          221               25                 765               57              845              62               983                72

                          DELTAIC COAST                               267               59                 421               78              467              86               552             102
                                                                                                          1552)          11021             [6051           fill]              [6961          [1281


                          TEXAS                                       109               55                 210             122               229            132                268             153


                          CALIFORNIA/HAWAII                           100               26                 274               83              317              96               392             119

                          COLUMBIAN/ALASKA                               19                2                41               3               46               4                55                 5

                          NATIONAL TOTAL                             2,417              276              4,516            554              5,006            613              5932             726
                                                                                                        [4,6471          [5781           [5,1441           [6381           [6,0761           [7521




                                                       Values in brackets are based on a subsidence rate of T/century for Louisianna








           5.0 ECONOMIC IMPLICATIONS FOR THE NFIP
              -   A summary of the assumptions and considerations that relate to the
           insurance implications is provided below:
                  1.    The current elevation distribution of post-FIRM construction
                        (policies) relative to the BFE, is assumed to hold for future
                        construction.
                  2.    The obsolescence of buildings is not accounted for; realistically, the
                        number of pre-FIRM and post-FIRM buildings built to outmoded BFE
                        standards would decline with time. Replacement structures would
                        be in compliance with NFEP regulations in effect at the time of their
                        construction. Thus, loss expectations may be overestimated.
                  3.    All monetary figures reflect 1990 dollars.
                  4.    This study examines the standard flood insurance coverage and not
                        the expanded benefits afforded by the Upton-Jones Amendment.


           5.1 Background
                  The NFIP is a risk management program for the Nation's floodplains that
           emphasizes loss control, effected at the local level, and risk transfer, through an
           insurance mechanism that pools risks on a nationwide basis. The costs of
           implementing the Program's loss control measures are balanced with the
           concerns of pricing the insurance. Sea level rise could have implications for the
           insurance rating structure that protects the financial soundness of the NFIP and
           for the Program's loss control requirements that are promulgated as the baseline
           for local community participation. -
                  In assessing the potential impact of sea level rise, this study examines the
           sensitivity of the NFIP's rate structure to the changing conditions as an
           indication of the degree to which Program changes would have to be made and of
           the criticality of the timeframe in which such changes might be needed. If rates
           can remain reasonable, then other risk management measures, while still
           beneficial, are not as necessary as in the case of the rating structure becoming
           unreasonable.





                                                   50








                   The analysis of the impact of sea level rise on the NFIP premium
            requirements has been done at a national level viewpoint since rates are set on a
            national risk classification basis. Although, even without sea level rise
            considerations, there are regional    differences in flood risk, a national rating
            structure provides administrative simplification and better meets the concerns of
            spreading the risk. Some regionalized loss control measures might be needed to
            respond to sea level rise, but the criticality of these measures to the NFIP can be
            examined within the context of the national insurance capability.
                  The impact of sea level rise in this study was limited to the standard flood
            insurance coverage provided to buildings insurable under the NFIP and not the
            additional erosion benefits afforded by the Upton-Jones Amendment (Section
            1306[c] of the National Flood Insurance Act of 1968). The FIA has long expressed
            two major objections to the Upton-Jones Amendment. One is that the actuarial-
            premiums, required by the NFIP legislation, could very well be unaffordable, thus
            making the risk uninsurable, and the other is that the Amendment does not
            include any loss control requirements. The effects of a rising sea level merely
            exacerbate these problems. While this sea level rise study has been underway, a
            bill has been introduced in Congress to repeal Upton-Jones and to create an
            erosion management program under the NFIR The effect of sea level rise on
            erosion management requirements and any insurance coverage that might be
            provided would be better examined during the development of regulations
            implementing that program.


            5.2 Methodology
                  For purposes of assessing the potential impact of sea level rise on the NFIP
            and the resulting revisions of premium charges that might be necessary to
            maintain adequate policyholder funding of the loss payments, a model
            representing the shifting distribution of risk characteristics of NFIP business was
            created to examine the relative changes in expected annual losses for policies in
            SFHAs. While a rising sea level exacerbates the flood risk, the expansion of the
            areas exposed to that risk also has the effect of increasing the number of flood



                                                    51







            insurance policies and thus increasing the premium income available to pay
            losses. By focusing on rates per $100 of insurance in force, the relative magnitude
            of the problem could be analyzed without a detailed projection of the NFIP's future
            book of business. No matter how much insurance will actually be in force in the
            areas affected by sea level rise, the changes in the average rates projected by the
            model are an indication of how sensitive the NFIP will be to the phenomenon and
            whether existing rate structures will be adequate to address the problem of
            maint  aining an overall premium income level commensurate with the level of
            losses.
                   The NFIP uses the elevation of the lowest floor relative to the BFE as one
            indicator of risk for an insured property. Depth-damage relationships and flood
            elevation-frequency relationships are used to calculate actuarial rates, which
            reflect expected annual damages and vary according to location relative to the
            BFE. For the purposes of this study, representative rates were computed for A-
            Zones using a 1-4 Family/One Floor-No Basement building as a model, and for V-
            Zones using a No Obstruction building as a model. These particular rates
            (expressed in dollars per $100 of coverage) are not paid by all policyholders.
            However, since it is   the relative change over time of the average rate based on
            damage expectations, and consequently the premium income level, that is of
            interest, these rates are adequate to examine increases in losses and to judge how
            the overall premium level would need to change as risk conditions are modified by
            a rising sea level.
                   To estimate expected losses, it was necessary to develop the distribution of
            household elevations relative to the BFE. In this study it was assumed that future
            floodprone households added due to population change and A-Zone floodplain
            expansion will reflect the elevation distribution of existing         post-FIRM flood
            insurance policies. Post-FIRM households added to the V-Zone due to its
            movement inland were assumed to follow a distribution 2 feet lower than existing
            post-FIRM policies in order to reflect the addition  al hazard of wave action. It was
            also assumed that all pre-FIRM households, for which the NFIP has no elevation
            data, followed an elevation distribution that was developed in such a way that it
            could be expected to produce results similar to actual loss experience. The


                                                      52






             number of pre-FIRM households was estimated by assuming that the county
             population/household figures for the year 1980 reflect pre-FIRM conditions.
             Households added to the floodplain after 1980 due to changes in population were
             considered post-FIERM. In addition, a distinction was made between pre-FIRM A-
             Zone and pre-FIRM V-Zone household elevation distributions. Because of the
             limited differences noted in data obtained from actual policies, only one post-
             FIRM household elevation distribution wqs adopted in this study for both A- and
             V-Zones. The exception.to this was the aforementioned 2-foot adjustment for post-
             FIRM buildings added to the V-Zone as it shifts inland.                    Graphical
             representations of these distributions are shown in Figures 5. 1A, 5. 1B, and 5.2.
                   The next step in the study required the calculation of the elevation
             distribution at the milestone time points previously discussed. For the pre-FIRM
             group, the elevation distribution was recalculated at each milestone year
             assuming a 1.0-foot increase in BFE and that households below -5.0 feet would
             drop out of the population. For the post-FIRM category, it was also necessary to
             account for the introduction of new households where the construction during
             each time period would be built to increasing BFE requirements.
                   A weighted average elevation and average insurance rate that reflect the
             distributions as a whole were computed for each milestone for each risk category
             including, for each of the A- and V-Zones, pre-FIRM subsidized and post-FIRM
             actuarially rated. In the case of the latter category, the average elevation and rate
             reflect that, as the BFE changes and is shown on the FIRMs, construction after
             that point takes place in compliance with the new BFE. An increase of sea level
             would cause some households in the current A-Zone to be in a V-Zone. This is due
             to increased wave heights associated with sea level rise. In order to account for
             these households, a 2-foot shift was incorporated in the distribution of household
             elevations with respect to the BFE. At the milestones, the average full risk
             premium rate was used to represent what would have to be charged in order to
             meet the expected annual losses at that point in time for those buildings,in areas
             subject to the effects of sea level rise.








                                                      53






                    0.32


                    0.30

                                           Average Elevation            -2.6 ft
                    0.28-


                    0.26


                    0.24-


                    0.22


                    0.20


                    0.18-


                    0.16-
               0


                                                                                           I-Ei
                    0.14-


              0     0.12-


                    0.10


                    0.08-


                    0.06-


                    0.04-



                                                                                                             . . . ... . ..
                                                                                                . ........   ........
                                                                                                  .. ........ ........
                                                                                                . ..... .    ........
                                                                                                      ...... .. ........
                                                                                                . . ........ ........
                                                                                                 .. ........ ........
                                                                                                  .. ........ ...
                                                                                  ......       . ........    ........
                                                                                               . . ........  ........
                                                                                                 . ........  ........
                                                                                                      ........ ........
                                                                                                  . ........ ........
                                                                                                      ........ ........ ...
                                                                                                          .. ........
                                                                                                      ........ ........
                                                                                  ........            ........ ........
                                                                                  ........            ........ .......
                                                                                  .......       .. ........  .......
                                                                                                .*: . ........ ........
                                                                                                 . ... ...   .......
                                                                                                          .... ........
                    0.02-
                                                                                        .... .....




                                                                                            ..            . ......
                          0                                                                               .. ........
                                8 7         6      5     4      3 2 1              0      1     -2    -3     -4    -5

                                            Bevation in Reference to BFE (feet)
                Figure 5.1A : 1990 Representative Pre-FIRM Distribution (V-Zone)





           0.40





           0.35-


                      Average Elevation -2.1 ft


           0.30-

                                                 Mi




           0.25 -





           0.20-





           0.15





           0.10-





           0.05-





              0
                8   7 6   5 4    3  2   1  0   1 -2  -3 -4  -5


                       Elevation in Reference to BFE (feet)

         Figure 5.1 B1990 Representative Pre-FI RM Distribution (A-Zone)









             0.28


             0.26-


                      Average Elevation 1.8 ft
             0.24-
                                                A'.
             0.22-


             0.20-
                                                     HE

             o.18-


             0.16

          0
             0.14-


         *(Z o.12-


             0.10-


             0.08

                                            .........


             0.06-                      . .........
                                          . ........


             0.04






                                                                        F777
             0.02-     m I      I    ...
                0-

                    8   7 6      5  4    3   2   1   0 -1    -2 -3 -4 -5


                            Elevation in Reference to BFE (feet)

                   Figure 5.2 :1990 Representative Post-FIRM Distribution








            5.3 Impact on Insurance Premium Requirements
                   Figures 5.3 through 5.6 show how the average full risk premium rates
            change as the actual risk changes through time. Again, it is the relative change
            that is important and not the specific rates in this modeling exercise. For
            example, in the 3-foot rise scenario, the average rate for A-Zone actuarial policies
            in 1990 is $.19 based on an average building elevation of 1.8 feet above BFE. In 2100,
            the average full risk premium rate is $.57 based on an average building elevation
            of 0.1 foot below BFE (see Table 5.1A). Thus, in order to maintain actuarial
            soundness for policies issued -in this risk category subject to sea level rise, the
            average premium would have to increase by 200 percent, because expected annual
            losses increase by that amount. Likewise, in order to maintain the current
            approximately 67 percent level of subsidy of pre-FIRM A-Zone policies subject to
            sea level rise, the average premium would have to increase by 144 percent over
            what it is today (see Table 5.1B).
                   It should be apparent that many assumptions underlie these results. The
            model  is only an approximation, and the inclusion of other considerations could
            very well raise or lower the projections. One aspect of the      effect of time on the
            NFIP's policy base that has not been included, and merits particular mention, is
            the gradual depletion of the older building stock. Certainly in the 'case of pre-
            FIRM buildings, over the course of 100 years the Program will be insuring a
            dwindling number, some buildings       being lost to flooding, some suffering other
            damage, but most merely coming to the end of their useful lives and being
            replaced by new buildings compliant w   ith the BFE in effect at that time. Even in
                                 TABLE 5.1A POST-FIRM ACTUARIAL
                                 INCREASE IN AVERAGE PREMIUMS
                           FOR BUILDINGS SUBJECT TO SEA LEVEL RISE
                       REQUIRED TO MAINTAIN ACTUARIAL SOUNDNESS


                                        ZONE A                          ZONE V
                          Full Risk                        Full Risk
                          Premium Rate       Percent       Premium Rate        Percent
                          1990 2100           Change       1990 2100           ChanEe


            1-Foot
            Rise          0.19 0.30            58%         0.66   0.90          36%


            3-Foot
            Rise          0.19 0.57           200%         0.66   1.33         102%



                                                      57






                  Figure 5.3        1 -Foot Sea Level Rise Scenario                     V-Zone

              8.00--






              7.00--
                          V-Zone Subsidized (Actual Risk)
                          V-Zone Actuarial (Actual Risk)           x------ x


              6.00         V-Zone Subsidized Current Rate is $0.50 per $100 Coverage
                           V-Zone Actuarial Current Rate is $0.66 per $100 Coverage

          0
          0          (2DWeighted average elevation of lowest floor for the milestone year
          C)
          0   5.00--

          69.

          W



          CZ
          75  4.00--



          CZ
          rr
          E
          .2  3.00
          E



          Cn
          rr                  2.6
              2.00--       C@D



              1.00
                                        ---------------------------------------------------            x
                               x



              0.00
                        1980        2000          20'20       2040          2060        2080          21;00

                                                             Year






              Figure 5.4      1 -Foot Sea Level Rise Scenario            A-Zone




             CO
               7
                     A-Zone Subsidized (Actual Fisk)
                     A-Zone Actuarial (Actual Risk)    x------x


            --0
                     A-Zone Subsidized C u* rrent Rate is $0.39 per $100 Coverage
                     A-Zone Actuarial Current Rate is $0.19 per $100 Coverage
         C
                          Weighted average elevation of lowest floor for the milestone year
           5. 07






            4.00





        rr

                                                                                GD
           2
             101
            .C







            1.00
                                                                                GD
                      CE)                                                           x
                          x-------------------------------------------------------------
            0.00
                   1980       2000      2020       2040       2060      2080       2100

                                                 Year






                     Figure 5.5            3-Foot'Sea Level Rise Scenario                              V-Zone

                8.00--



                7.00--          -Zone Subsidized (Actua
                              V                                     I Risk)
                              V-Zone Actuarial (Actual Risk)                  x ------  x
             -6.00--          V-Zone Subsidized Current Rate is $0.50 per $100 Coverage
                              V-Zone Actuarial Current Rate is $0.66 per $100 Coverage
             CZ
             >                      Weighted average elevation of lowest floor for the milestone year
             0

             C) 5.00--


             2

             CL


             CZ
             7Ej 4.UU--





                3.00--                                                                                 3.9




             CC 2.00--
                                       -----------
















                0.00-
                           1980           2000            2020           2040            2060          2080            2@00

                                                                       Year








                      Figure 5.6        3-Foot Sea Level Rise Scenario                      A-Zone

              8.00



              7.00        A-Zone Subsidized (Actual Risk) e-9
                          A-Zone Actuarial (Actual Risk) x          ------  x

              6.00        A-Zone Subsidized Current Rate is $0.39 per $100 Coverage
                          A-Zone Actuarial Current Rate is $0.19 per $100 Coverage
                               Weighted average elevation of lowest floor for the milestone year
          O>

              5.00




          CL


          CU
          =   4.00
          0




          CZ

          E   3.00
          E                                                                               3.9

          Cn
              2.00




                             (
                               2. 1)
                               @D
              1.00
                                                                                                     GD
                             GD                                              ------------  x----------  Ix
                                x------------------------------
              0.00
                        1980         2000          2020        2040          2060        2080          2100

                                                              Year









                                           TABLE 5.1B PRE-FIRM SU13SIDIZED
                                          INCREASE IN AVERAGE PREMIUMS
                                 FOR BUILDINGS SUBJECT TO SEA LEVEL RISE
                           REQUIRED TO MAINTAIN CURRENT SUBSIDY LEVEL*


                                         ZONE A                                   ZONE V
                                Subsidized                                Subsidized
                                  Rate             Percent                 Rate             Percent
                                1990 2100**       Chanae                  1990 2100' Change


               1-Foot
               Rise             0.39 0.60            54%                  0.50 0.63           26%


               3-Foot
               Rise             0.39 0.95           144%                  0.50 0.79           58%


               *Curren, subsidy level is estimated to be 67% IA-Zone) and 76% (V-Zone) based on average $.39 (A-Zone) and
               $.50 (V-Zone) rates charged compared with average full risk premium rates in 1990 of $1.18 (A-Zone) and
               $2.09 (V-Zone).

               **2101 subsidized rates equal 0.33 (A-Zone) and 0.24 (V-Zone) times the average full risk premium rate. While
               this calculation produces a V-Zone rate that falls below the A-Zone rate, it is assumed that this would not
               actually be allowed to happen.


               the case of post-FIRM construction, in the long timeframes Associated with
               estimates of sea level rise, there will be older buildings which will be constructed
               to outmoded BFE standards and will be removed from the book of those being
               insured. Because this depletion has not been included, the argument can be made
               that the estimates of future annual damage expectations are high. Of course,
               there are also arguments that can be made for these estimates being low. Suffice
               it to say that there is a fair amount of uncertainty in these figures that should be
               borne in mind when using them.
                       So far, the relative change in rates, as an indicator of increased loss
               expectations and resulting premium increases, has been emphasized. However,
               it is also important to examine the magnitude of the rates in assessing the
               potential impact on the NFIP. One reason for establishing the 100-year flood
               elevation as the BFE for post-FIRM construction was that owners of buildings
               constructed to this standard would be able to transfer the remaining risk through



                                                                   62







            the purchase of reasonably priced insurance.            The consideration of the
            affordability of full risk premiums for pre-FIRM construction, generally built to
            much lower standards, prompted Congress to "grandfather" in that existing
            construction at subsidized rates.
                  Under the 1-foot rise scenario, the average insurance rates for post-FIRM
            construction in V-Zones and A-Zones, over the course of 110 years, never rise
            above that currently charged for buildings @uilt to the BFE, a level that has already
            been deemed to provide insurance at a reasonable price. Even under the 3-foot rise
            scenario, these average rates do not become absolutely unreasonable. In the A-
            Zones, the rate is substantially less than that charged for buildings at 1 foot below
            the BFE. In the V-Zones, the rate is only 8 percent greater than that charged at 1
            foot below BFE. These results indicate that ample flexibility exists within the
            NFIP rate structure to accommodate the generation of enough premium, at
            reasonable rates, from the policyholder base to cover flood losses to the actuarially
            rated policies. The question arises as to how these premium charges should be
            distributed among the policyholder  s who have varying degrees of risk exposure.
                  The NFIP has long known and anticipated that risk conditions can change,
            precipitating a rise in an area's BFE. This possibility is not unique to coastal
            regions, but is an aspect of risk assessment in inland areas as well, where
            increased urbanization can easily cause a 1- to 3-foot rise in the BFE over time.
            All policies are subject to this additional risk. The rating structure currently
            considers unquantifiable effects of influences such as watershed urbanization
            and coastal erosion through the application of contingency loadings on the rates (5
            percent in A-Zones and 10 percent in V-Zones) and the establishment of
            minimum rates for insurance.
                  A 1-foot rise in sea level over 110 years would not seem to tax the NFIP's
            ability to apply- current approaches in spreading the costs over all post-FIRM
            policyholders. A 3-foot rise, or more, in sea level may require that additional
            measures be taken to distribute premium burdens equitably and avoid undue
            cross subsidies. In spreading the costs of the additional risk that flood hazard
            conditions may worsen, current program rules allow post-FIRM buildings, built
            in compliance with NFIP requirements at the time of construction, to retain their


                                                     63







            original risk classification. This grandfathering may have to be modified so that
            more of the additional costs are borne by the owners of the buildings subject to
            worsening conditions rather than by the group of insureds as a whole. One
            mechanism might be to always rate structures according to current risk
            .conditions, but capping the rates for the buildings previously built in compliance.
            Furthermore, if the relative homogeneity of the nationally used risk zones is
            disrupted by inordinate numbers of buildings becoming more flood prone due to
            sea level rise than due to other factors common also to inland areas, then it may
            become necessary to create coastal A-Zones that are distinct from inland A-Zones.
            Rate loadings could also be increased to build reserves in anticipation of later
            losses.
                   As mentioned already, there will be a continuously decreasing number of
            pre-FIRM buildings that the NFIP will be insuring and therefore a dwindling
            number that will remain long enough to be affected by sea level rise in the
            contemplated timeframes. The model's results indicate that the rates necessary
            to maintain   current levels of subsidy reach amounts that are probably higher
            than those, at least currently, considered to be affordable. Thus, it is likely that, for
            however many pre-FIRM buildings are still insured, the subsidies would
            increase. If there really were to be substantial numbers of these structures
            remaining long enough to be affected by sea level rise (which is highly unlikely),
            then it seems that other program changes, besides insurance methods, would
            have to be employed in order to reduce taxpayer subsidies going to this older
            construction.


            5.4 Impact on Losses
                   Because of the relatively long timeframe in which sea level rise would affect
            flood risk conditions, it is essentially an issue concerning post-FIRM construction.
            Owners of these buildings are charged full risk premiums under the NFIP so that
            losses over the long term are fully funded by the policyholders. However, the
            ability to appropriately price the transfer of risk through insurance does not mean
            this mechanism is the only risk management tool that should be employed. The




                                                       64







             efficiency of loss control measures should also be explored and their costs
             balanced against those of insurance.
                   To provide some order of magnitude estimates of the additional flood losses
             that can be expected due to sea levelrise, NFIP underwriting experience data
             from 1978 - 1989 were used in conjunction with the household data and indicated
             premium increases developed'for this report. Because the NFIP experience
             period of 12 years is relatively short for its being employed in the analysis of a low
             probability event such as flooding, t    he most credible use of the data is at the
             national level. Therefore, these flood loss estimates were made for all areas
             affected by sea level rise on a national basis.
                   Assuming a 45-percent market penetration of households located in the
             coastal areas affected by sea level rise and expressing the amounts in constant
             current dollars (i.e., no trending for future inflation), a 1-foot rise in sea level will
             gradually increase the expected annual NFIP flood losses by about $150 million by
             the year 2100. Similarly, a 3-foot rise will gradually increase expected annual
             losses by about $600 million by the year 2100. To help put these amounts in
             perspective for insurance purposes where the risk is spread over all policies
             subject to sea level rise, expected annual losses per policy in the year 2100 would be
             about $60 more than today unde      r the 1-foot rise scenario and about $200 more
             under the 3-foot rise scenario. If expected losses were examined either on a
             regional basis or an individual building basis, the amounts could differ
             significantly from these figures. This would have great importance for local loss
             control decisions.


             5.5 Program Impact-
                   The impact of potential sea level rise and the development of an appropriate
             Program response must be considered and prioritized within the context of many
             NFIP concerns. From the standpoint for insuring against flood losses through a
             system of pricing that is fair and that protects the NFIP's financial soundness,
             sea level rise does not pose any immediate problem. Currently, 74 percent of the
             post-FIRM structures insured in A-Zones and V-Zones have been built to
             elevations at least 1-foot higher than the BFE. Thus, new construction is well



                                                       65







            protected. The rating system for flood insurance appears to be able to reasonably
            respond to the pricing changes that would be necessitated by a 1-foot rise in sea
            level by the year 2100. Even under the 3-foot scenario, a rise of 1 foot is not expected
            until the year 2050. Although this scenario might eventually call for more
            extensive adjustments to the insurance system, there are no changes needed so
            soon that at least another 20 years cannot be used to fir'st gather more definitive
            information concerning sea level rise.
                   The ability of the insurance system to absorb the costs of the additional risk
            posed by a rising sea level does not mean that other risk management efforts may
            not be appropriate. The concerns of a particular region or locality may produce a
            different perspective on the priority of sea level rise than at the national level for
            the NFIP. The costs and benefits of implementing other risk management
            measures must be balanced with the option of risk transfer through an insurance
            mechanism. However, this is no different than other issues the NFIP already
            faces in fashioning a national level response to flood hazards that can vary widely
            around the country. The recently implemented NFIP Community Rating System,
            by providing community-wide credits on flood insurance premiums, is designed to
            recognize and encourage State and local floodplain management efforts that go
            beyond minimum national requirements. A number of the activities recognized
            in this system are also potentially very effective in mitigating the impact of sea
            level rise (e.g., freeboard above BFE and open space policies).
                   This study has considered only the impact of sea level rise on the provision
            of the standard flood insurance coverage. The provision under the Upton-Jones
            Amendment of relocation and demolition coverage for buildings subject to
            imminent collapse due to the effects of erosion has not been considered. The costs
            of continuing to provide these automatic insurance policy benefits could
            eventually be increased by the effects of sea level rise. However, a bill recently
            introduced in Congress would repeal this benefit, substituting a mitigation
            assistance program that would prioritize and fund relocation projects within a
            specified budget.       Additionally, the bill would create a coastal erosion
            management component of the NFIP. Erosion management activities in




                                                       66






             combination with the repeal of the Upton-Jones insurance policy benefits would
             tend to further reduce the potential effects of sea level rise on the NFIP.


             5.6 Study/Mapping Requirements
                   With a continuous rise in sea level, there will be a need to restudy and
             remap coastal flood hazard areas. Using the criterion that a restudy will be
             conducted when sea level has risen 1 foot, the first restudy would occur in the
             years 2050 and 2100 for the 3- and 1-foot scenarios, respectively.
                   An estimate was made of the cost of updating and revising the technical
             studies and accompanying mapping for the counties directly affected by a rise in
             sea level. This estimate is based on the cost of past studies involving storm surge
             and wave analyses and the preparation of revised FIRMs. The cost associated
             with these efforts was expressed in terms of the cost per county for the technical
             study and the cost per map panel for the mapping and distribution process. The
             average cost of conducting the technical study was estimated to be $150,000 per
             county. The total cost of preparing revised mapping was estimated to be $1500 per
             map panel. For each county, the number of FIRM panels affected was determined
             by computing the ratio of the current coastal floodplain area to the total floodplain
             area and multiplying this ratio by the total number of panels in the county. The
             costs for the individual counties were then summed. For counties with less than
             10 FIRM panels affected by sea level rise the costs for conducting the technical
             study and mapping ($150,000)'were excluded.
                   The total number of counties estimated to be affected by sea level rise is 283.
             Approximately 5,050 map panels in these counties will need to be revised for each
             1-foot rise in sea level. The total cost associated with the restudy and remapping of
             these counties is estimated to be $30,000,000, which would be spread over a 4- to 5-
             year period. These figures do not reflect the possibility that coastal studies and
             maps are likely to be revised for reasons other than sea level rise. Such a
             consideration would show a substantial reduction in the actual cost of study and
             map revisions directly associated with sea level rise.





                                                      67









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                                                   71






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