Abstract
Understanding
the broad-scale ramifications of accelerated sea level rise requires
maps of the land that could be inundated or eroded. 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. This paper uses the USGS 1-degree
digital elevation series and NOAA shoreline data to illustrate the
land below the 1.5- and 3.5-meter contours for areas the size of
entire U.S. states or larger.
Because sea
level is expected to rise about 60 cm (2 feet) along most of the
U.S. Gulf and Atlantic Coast in the next century (EPA 1995), it
would be preferable to illustrate the land that would be inundated
with a 30 or 60 cm (1 or 2 foot) rise in sea level. Unfortunately,
the 1.5-meter (5-foot) contour is the lowest elevation that can
be consistently illustrated over large regions with the available
digital data.
This does not
mean, however, that these maps show the land that would be flooded
with a 1.5-meter (5 foot) rise in sea level. 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. Although tide ranges
vary, mean spring high water (i.e. the typical high tide during
new moon and full moon) is typically 60 cm above mean sea level.
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. Such a rise appears to be most likely to occur in the
next 120 years, but has a 1% chance of occuring in the next 60 years.
(See EPA 1995.)
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. |
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