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EPA's Bush-era sea level rise study

Part 1: Coastal Elevation Mapping

James G. Titus and Jue Wang. 2008. Maps of Lands Close to Sea Level along the Middle Atlantic Coast of the United States: An Elevation Data Set to Use While Waiting for LIDAR. In Background Documents Supporting Climate Change Science Program Synthesis and Assessment Product 4.1. Edited by James G. Titus and Elizabeth M. Strange. 2008. Washington, D.C.: U.S. Environmental Protection Agency. pp 1-44. EPA 430-R-07-004.

The summary is on this page. You can also download a printer quality version of this sea level rise mapping study (pdf 2.1 MB, 44 pp).


This report provides a coastal elevation data set for the mid-Atlantic for purposes of assessing the potential for coastal lands to be inundated by rising sea level. Depending on what we were able to obtain, our elevation estimates are based on LIDAR, federal or state spot elevation data, local government topographic information, and USGS 1:24,000 scale topographic maps. We use wetlands and tide data to define a supplemental elevation contour at the upper boundary of tidal wetlands. Unlike most coastal mapping studies, we express elevations relative to spring high water rather than a fixed reference plane, so that the data set measures the magnitude of sea level rise required to tidally flood lands that are currently above the tides. Our study area includes the seven coastal states from New York to North Carolina, plus the District of Columbia.

We assess the accuracy of our approach by comparing our elevation estimates with LIDAR from Maryland and North Carolina. The root mean square error at individual locations appears to be approximately one-half the contour interval of the input data. We also compared the cumulative amount of land below particular elevations according to our estimates and the LIDAR; in that context, our error was generally less than onequarter the contour interval of the input data.

We estimate that the dry land in the region has a relatively uniform elevation distribution within the first 5 meters above the tides, with about 1,200–1,500 km2 for each 50 cm of elevation. With the exception of North Carolina, the area of nontidal wetlands declines gradually from about 250 km2 within 50 cm above the tides to about 150 km2 between 450 and 500 cm above the tides. North Carolina has approximately 3,000 km2 of nontidal wetlands within 1 meter above spring high water; above that elevation, the amount of nontidal wetlands declines gradually as with the other states. North Carolina accounts for more than two-thirds of the dry land and nontidal wetlands within 1 meter above the tides.

We also compare our results to previous studies estimating the region's vulnerability to sea level rise. Our results are broadly consistent with an EPA mapping study published in 2001, which estimated the total amount of land below the 1.5- and 3.5-m contours (relative to the National Geodetic Vertical Datum of 1929). This study appears to be a significant downward revision, however, of EPA's 1989 Report to Congress. Our estimates of the dry land vulnerable to a 50- or 100-cm global rise in sea level are less than onehalf the estimates of the Report to Congress. The regional estimates of that nationwide study, however, were based on a small sample. Therefore, one should not extrapolate our mid- Atlantic result to conclude that EPA’s previously reported nationwide estimate overstates reality by a similar magnitude.

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