National Assessment of Coastal Vulnerability to Sea-Level Rise: Preliminary Results for the U.S. Atlantic Coast
A map of the coastal vulnerability index (CVI) for the U.S. East
Coast is shown in Figure 1. The
calculated CVI values range from 1.22 to 39.52. The mean CVI value is
14.75; the mode is 24.49; and the median is 15.49. The standard
deviation is 7.7. The 25th, 50th, and 75th percentiles are 8.7,
15.6 and 20.0, respectively.
Figure 2. Histograms showing the frequency of occurrence and cumulative frequency of coastal vulnerability index (CVI) values for U.S. Atlantic coast.The vertical red lines delineate the chosen ranges for low, moderate, high, and very high risk areas
Histograms of the CVI values are shown in Figure 2. The CVI scores are divided into
low, moderate, high, and very high-risk categories based on the quartile ranges and visual inspection of the data (Figure 2). CVI values below 8.7 are assigned to the low risk category. Values from 8.7-15.6 are considered moderate risk. High-risk values lie between 15.6-20.0.
CVI values above 20.0 are classified as very high risk.
Figure 3 shows a bar graph of
the percentage of shoreline in each risk category. A total of 9,472
km of shoreline is ranked in the study area. Of this total, 27
percent of the mapped shoreline is classified as being at very high
risk due to future sea-level rise. Twenty-two percent is
classified as high risk, 23 percent as moderate risk, and 28
percent as low risk.
The mapped CVI values (Figure
1) show numerous areas of very high vulnerability along the
coast, particularly along the mid-Atlantic coast (Maryland to North
Carolina) and northern Florida. The highest vulnerability areas are
typically high-energy coastlines where the regional coastal slope
is low and where the major landform type is a barrier island. A
significant exception to this is found in the lower Chesapeake Bay.
Here, the low coastal slope, vulnerable landform type (salt marsh)
and high rate of relative sea-level rise combine for a high CVI
The coastline of northern New England, particularly Maine,
shows a relatively low vulnerability to future sea-level rise. This
is primarily due to the steep coastal slopes and rocky shoreline
characteristic of the region, as well as the large tidal range.