Producing such maps requires a combination of elevation information and models of shoreline erosion, wetland accretion, and other coastal processes. Assessments of coastal areas in the United States that combine all of these factors have focused on relatively small areas, usually 25 to 30 kilometers wide. In many cases, the results are as sensitive to uncertainty regarding geological processes as to the rate of sea level rise. This paper presents maps illustrating the elevations of lands close to sea level. Although elevation contours do not necessarily coincide with future shorelines, the former is more transparent and less dependent on subjective modeling.
Several methods are available for inferring elevations given limited data.
For a variety of reasons, the 1.5-meter contour is only about 1.3 meters above mean sea level along most of the Atlantic and Gulf Coasts. Therefore, the 1.5 meter contour roughly represents the area that would be inundated during spring high water with a 70 cm rise in sea level. The maps imply that approximately 58,000 square kilometers of land along the Atlantic and Gulf coasts lie below the 1.5-meter contour. Louisiana, Florida, Texas, and North Carolina account for more than 80 percent of the low land. Outside of those four states, the largest vulnerable populated region is the land along the Eastern Shore of Chesapeake Bay stretching from Dorchester County, Maryland to Accomac County, Virginia.