1998 Year of the Ocean Impacts of Global Climate Change 



Many coastal structures were designed with the 100-year flood as their basis. This 

 flooding level determines the elevations to which the federal projects (such as U.S. Army's 

 Corps of Engineers levees that protect New Orleans) are built. It is also the level to which coastal 

 structures must be built to qualify for flood insurance through FEMA's Flood Insurance 

 Program. If sea level rises, the statistics used to design these structures change. A 50-year flood 

 may become as severe as (or even more severe than) a 100-year flood before sea-level rise. 

 Coastal insurance rates would be adjusted to reflect such increased risk. Furthermore, FEMA 

 estimates that with a sea-level rise of one meter, the number of households in the coastal 

 floodplain would increase from 2.7 million to 6.6 million by 2100. This growth will be the result 

 of sea-level rise as well as the increase of coastal population. In some areas however, structures 

 will be upgraded as sea level rises so that flood risks will not increase. 



Coastal wetlands are already eroding in most states (see Table 2), particularly Louisiana 

 and Maryland. For example, Louisiana's coastal area lost an estimated 3,950 square kilometers 

 of wetlands from 1930 to 1990. This loss of wetlands resulted, for the most part, from flood- 

 protection levees along the Mississippi and artificial bank stabilization efforts to confine the flow 

 of the river and prevent the flooding, sedimentation, and freshwater supplies that occurred 

 naturally. Many wetland losses elsewhere result from draining or filling. In addition, large areas 

 of brackish and freshwater wetlands have become progressively more saline as salt water has 

 increasingly invaded the deteriorating coastal zone. Because 40 percent of U.S. coastal wetlands 

 are found in Louisiana, this loss constitutes about 80 percent of the total national coastal wetland 

 loss. Louisiana coastal wetlands are exceptionally valuable in terms of coastal fisheries and 

 migratory waterfowl, protection of low-lying population centers from hurricanes and other 

 storms, and oil and gas production. Furthermore, the greatly accelerated rates of coastal wetland 

 loss appear to be the unintended result of massive human disturbances of these wetlands and 

 intervention (for purposes of flood protection, water supply, maritime commerce, energy 

 production, and wildlife management) in the processes that sustain coastal wetlands. 



Wetlands require a delicate balance of sediment, fresh and salt water and are particularly 

 vulnerable to inundation and erosion as a result of sea-level rise. Coastal wetlands are also 

 vulnerable to changes in the source or decreased flux of fresh water and sediment, if upstream 

 areas become more arid. Wetlands naturally migrate as land subsides and sediment supply 

 changes, but migration has been limited in several areas by the encroachment of urban areas 

 which utilize sea walls and other protective structures. In addition, the possible rate of sea-level 

 rise predicted by some climate change models is more rapid than the natural rate of wetland 

 migration, thus wetland losses will likely increase. 



Estuarine beaches are also at particular risk to sea-level rise. They are much more 

 vulnerable than ocean beaches because they tend to be narrower and policies against shoreline 

 armoring generally apply to oceans but not to bays. Also, they are more vulnerable than 

 vegetated wetlands because the wetland protection programs tend to focus on the total area of 

 wetlands protected and because beaches are narrow, they do not represent much acreage. The 

 loss of these beaches would effect species such as horseshoe crabs and the birds that feed on 

 them, as well as terrapins, least terns, and tiger beetles. 



G-32 



