Projected Impact of Relative Sea Level Rise on the National Flood Insurance Program
Projected Impact of Relative Sea Level Rise on the National Flood Insurance Program (PDF, 70 pp., 692 kb) was originally published October 1991 by the Federal Emergency Management Agency, Flood Insurance Administration.
Executive Summary
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 3-foot 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 3-foot 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 3-foot 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 1-foot rise in sea level, there are no immediate program changes needed. However, the possibility exists for significant impacts in the long term; therefore, the Federal Emergency Management Agency (FEMA) should:
- continue to monitor progress in the scientific community regarding projections of future changes in sea level and consider follow-on studies that provide more detailed information on potential impacts of sea level rise on the NFIP;
- in the near term, consider the formulation and implementation of measures that would reduce the impact of relative rise in sea level along the Louisiana coast; and
- strengthen efforts to monitor development trends and incentives of the Community Rating System that encourage measures which mitigate the impacts of sea level rise.
Projected Impact of Relative Sea Level Rise on the National Flood Insurance Program (PDF, 70 pp., 692 kb) was originally published October 1991 by the Federal Emergency Management Agency, Flood Insurance Administration