U.S. vulnerability to sea level rise
In the last century, sea level rose 5 - 6 inches (13 - 15 cm) more than the global average of 7 inches (18 cm) along the U.S. Mid-Atlantic and Gulf Coasts, because coastal lands there are sinking. Over 50% of the U.S. coastline is vulnerable or highly vulnerable to sea level rise, according to the Coastal Vulnerability Index (CVI) developed by the United States Geological Survey (USGS). In the U.S., relative sea level rise (the combined effects of global sea level rise plus the fact the land is sinking) is highest along the Mississippi River Delta in Louisiana, where relative sea level rises of 3.2 ft (.98 meters) have been observed during the 20th century. This is one of the highest relative sea level rises in the world. According to the NOAA Tides and Currents sea level rise interactive tool, the U.S. tide gauges that have shown the highest rates of sea level rise over the past century are at Grand Island, LA (1.8 ft rise since 1947), Galveston, TX (1.1 ft since 1957), and Chesapeake Bay, VA (0.6 feet since 1975). Alaska and some areas along the Pacific Northwest coast are at low risk of sea level rise, because the relative sea level is actually falling at present. Land in these regions is rising as it recovers from removal of the weight of the great ice sheets that covered much of North America during the last Ice Age. For example, relative sea level at Kodiak Island, Alaska has fallen by 1.1 feet since 1975, despite the fact global sea level has been increasing.
Figure 1. Twentieth century annual relative sea-level rise rates in mm/year along the U.S. coast. The higher rates for Louisiana (9.85 millimeters [mm] per year, about 3.3 ft/century) and the mid-Atlantic region (1.75 to 4.42 mm per year, 0.6 - 1.4 ft/century) are due to land subsidence. Sea level is stable or dropping relative to the land in the Pacific Northwest, as indicated by the negative values, where the land is tectonically active or rebounding upward in response to the melting of ice sheets since the last Ice Age. Image credit: Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region (data from Zervas, 2001).
U.S. Coastal Vulnerability
The Coastal Vulnerability Index (CVI) takes into account six factors:
1) The geology of the coast. Barrier islands, river deltas, and marshes are the most vulnerable to erosion and sea level rise, while steep, rocky cliff shores are the least. Sheltered bays like Galveston Bay and Tampa Bay are less vulnerable than the exposed coasts. (Note, however, that hurricane storm surges are typically higher in sheltered bays, at least for slow-moving storms).
2) How steep the land near the coast is. Gently sloping lands are the most vulnerable. In the Gulf Coast region, the slope variable has the highest risk ranking along the Louisiana coast, the Texas coast north of Corpus Christi, and the southwest Florida coast.
3) The local rate of sea level rise. The sea level is rising faster along the western Gulf of Mexico than the eastern Gulf. The highest rates of sea-level rise in the Gulf of Mexico (and in the United States) are in the Mississippi delta region (10 mm/yr, or 1 inch/2.5 years).
4) The amount of shoreline erosion going on. Most of the U.S. coast is moderately or severely eroding, and very few areas are gaining (Figure 2).
5) The mean tidal range. Shores that have a large difference between low and high tide are less likely to get a significant storm tide--the height above mean sea level of the sum of the storm surge plus the tide. For example, in a region like Maine, which has a 12 ft range between low and high tide, a storm having a 9 ft storm surge will have a storm tide below local high tide for a quarter of a tidal cycle. Shores with a very narrow tidal range (e.g., the 2 ft tidal range common along the Texas and Louisiana Gulf Coast) will get a storm tide of 8 - 10 feet with the 9 ft storm surge in the above example. Shorelines with a narrow tidal range always get high storm tides regardless of when the storm surge hits.
6) How high the waves at shore are. Obviously, shores that experience higher wave heights are at greater risk. In the Gulf of Mexico, wave energy is highest along sections of the Texas coast and on the southern tip of the Mississippi delta.
Figure 2. Shoreline change around the United States based on surveys over the past century. All 30 coastal states are experiencing overall erosion due to natural processes (e.g., storms, sea-level rise) and human activity. If the shoreline is uncolored, no data was available. Image credit: USGS, 1985, and taken from Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region).
The Coastal Vulnerability Index (CVI) web page gives detailed maps of each section of the U.S. coast, along with specific reasons why each portion of the coast was assigned the ranking it got. A brief summary:
The Gulf Coast
The Gulf Coast has 55% of its length in the "very high" or "high" vulnerability range. Fully 41% of the coast falls in the "very high" range, far more than the 28% in that category along the Pacific coast and 23% along the Atlantic coast. The region around New Orleans is the most vulnerable region of the entire U.S. coast. The Florida Panhandle, as well as the West Florida coast, are at low to moderate risk because the land is not sinking much, wave heights are lower, and the slope of the land is relatively steep near the coast. The Texas coast is considered to be at a high to very high risk because of the relatively high mean wave height, sinking land, and shallow coastal slope.
The East Coast
The East Coast has 50% of its length in the "very high" or "high" vulnerability range. 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 value. 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.
The Pacific Coast
The Pacific Coast has 50% of its length in the "very high" or "high" vulnerability range. Areas of very high vulnerability include the San Francisco - Monterey Bay coast and in southern California from San Luis Obispo to San Diego, where the coast is most highly populated. The highest vulnerability areas are typically lower-lying beach areas. The low risk, least vulnerable areas generally occur at rocky headlands along cliffed coasts where the coastal slope is steep, relative sea-level is falling, tide range is large, and wave energy is lower. Examples of these areas are the northern coast of Washington, Monterey, and Cape Mendocino, California.
Figure 3. The Coast Vulnerability Index (CVI) for the U.S.
References
Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region.
National Assessment of Coastal Vulnerability to Sea-Level Rise: Preliminary Results for the U.S. Gulf of Mexico Coast (USGS, 2000).
Jeff Masters
Reader Comments
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h09 is that bertha
YAYA!
next
A winner --
Hey song
Name this retired major hurricane that caused over 2 billion dollars in damage and killed 200 people across 12 countries:
oops hold on wrong on elol just a sec
Name this retired major hurricane that caused over 2 billion dollars in damage and killed 200 people across 12 countries in the Caribbean and central America:
Says who ? I am down for the count anyhow. Be well all and CUL8R ª¿ª
mitch
Nope.
LMBO! I hate you! lol
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP022009
800 PM PDT TUE JUN 23 2009
SATELLITE IMAGERY INDICATES A RECENT BURST OF CONVECTION TO THE EAST
OF THE CENTER...THOUGH THE CONVECTION REMAINS RATHER ASYMMETRIC DUE
TO MODERATE NORTHEASTERLY SHEAR. IN SPITE OF THE CONVECTIVE
BURST...ANDRES HAS A RAGGED SATELLITE APPEARANCE WITH POORLY-
DEFINED BANDING FEATURES. FINAL DVORAK T-NUMBERS HAVE DECREASED
OVER THE PAST 6-12 HR...AND ON THIS BASIS ANDRES IS DOWNGRADED TO A
60 KT TROPICAL STORM. THE EARLIER DISPARITY BETWEEN SATELLITE AND
RECONNAISSANCE DATA SUGGESTS THAT GREATER-THAN-NORMAL UNCERTAINTY
IS ASSOCIATED WITH THIS INTENSITY ESTIMATE. THE OFFICIAL INTENSITY
FORECAST CALLS FOR A GRADUAL WEAKENING OVER THE NEXT 24
HOURS...MOSTLY A RESULT OF A PERSISTENT NORTHEASTERLY SHEAR OF 20
TO 25 KT AND A GRADUAL DECLINE IN OCEANIC HEAT CONTENT.
THEREAFTER...A STEADIER AND MORE RAPID WEAKENING IS PROJECTED ONCE
ANDRES REACHES EVEN COOLER WATERS...AND THE CYCLONE IS FORECAST TO
BE A REMNANT LOW BY 72 HOURS. THE INTENSITY FORECAST IS CLOSELY IN
LINE WITH BOTH SHIPS AND ICON.
ANDRES HAS RECENTLY TRACKED A LITTLE MORE TO THE LEFT...WITH AN
INITIAL MOTION OF 305/9. SEVERAL OF THE DYNAMICAL MODELS CONTINUE
TO INDICATE SIGNIFICANT INTERACTION BETWEEN THE CYCLONE AND THE
NEARBY MEXICAN LANDMASS...RESULTING IN AN ABRUPT DISSIPATION.
HOWEVER...THE GUIDANCE INDICATES MID-LEVEL RIDGING REASSERTING
ITSELF NORTH OF THE CYCLONE AS SOON AS 12 HOURS FROM NOW...WHICH
SHOULD CAUSE THE TRACK TO GRADUALLY BEND MORE WEST-NORTHWEST AS THE
CENTER MOVES AWAY FROM THE MEXICAN COAST. THE MORE LEFTWARD
INITIAL TRACK AND THE STRENGTHENING RIDGE ARE LIKELY INDICATIONS
THAT ANDRES SHOULD AVOID LANDFALL IN SOUTHWEST MEXICO BUT SHOULD BE
CLOSE ENOUGH TO CAUSE POSSIBLE TROPICAL STORM CONDITIONS. BY 48
HOURS...A WEAKER ANDRES SHOULD SLOW DOWN AND BE STEERED MORE TOWARD
THE WEST AS A RESULT OF WEAK LOW-LEVEL RIDGING FORECAST SOUTHWEST
OF BAJA CALIFORNIA.
July 10?
I didn't know you were gonna go sorry lol.
hey all you no what i small i small trolls
We're doing H2009's right now......and no you're wrong lol.
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