U.S. vulnerability to sea level rise

By: Dr. Jeff Masters , 4:04 PM GMT on June 23, 2009

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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

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Give us a little clue that includes a land mass!
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Wow it won't let me upload new images...one sec.
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Remember Ed..you cannot post...only answer...Let the games continue!
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Quoting GeoffreyWPB:
and remember all...only Levi and Hurricane can post to cause less confusion...Next one please!
OHHHHH ok.
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Just checking in.... Read the blog.... More "Global Warming/Climate Change/Man-made disaster/Al Gore's Pet Project" stuff.... Yay. Going to bed now.
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Ok....

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
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Quoting Levi32:


YAYA!


A winner --

Hey song
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and remember all...only Levi and Hurricane can post to cause less confusion...Next one please!
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could be alot of rain in swfl from tpa south tonight....the storms are starting to come off the water now as well...
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game over
next
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H2009, Hurricane Frederic caused 6.5 billion dollars in damage in 2009 dollars, not 2 billion dollars.
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Quoting hurricane2009:


FINALLY!!! LOL





Hurricane Frederic from 1979


YAYA!
Member Since: November 24, 2005 Posts: 635 Comments: 26685
Is it Michelle?
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Hurricane Eloise?
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Hurricane Frederic 1979? Can't remember if it's famous or not but whatever. You said it's supposed to be a forgotten storm right.
Member Since: November 24, 2005 Posts: 635 Comments: 26685
evening every one just checkin in

h09 is that bertha
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Would it be Elena '85?
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storms are firing amazing light show figures since thunderstorm watch just expired
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Hurricane Elena of 1985?
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Quoting KeepItSimple:
Here's a game: let's see how long it's going to be before XXXX gets banned for spamming the main blog with his own silly blog...
I got a better game lets see who has the biggest empty space in there head for that is what you are about to be replaced with empty space just like whats in your head
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opal
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ok we need a severe t-storm watch for swfl,the cape in the TPA's last sounding is 2600 and the precipitable water over the region is 2-2.2 inches!!!!
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Quoting Orcasystems:
Hmm a lot of lights on here tonight.. but it doesn't look like anyone is home.


Lights Are On But Nobody's Home

Could not stop my typing. . . . .
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Quoting KeepItSimple:
Here's a game: let's see how long it's going to be before Orca gets banned for spamming the main blog with his own silly blog...


I enjoy his blog. nothing silly
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Is it Cindy
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Hurricane Kate 1985?

[edit] wait that's famous lol
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Y'all amaze me with this hurricane history/trivia stuff...I can't even remember what I had for dinner...
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H2009, is it Hurricane Juan of 1985?
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yes..who can answer it firstest? I am stumped on this one.
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Hmm a lot of lights on here tonight.. but it doesn't look like anyone is home.
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Rules of the Road

Seriously, no spamming. Spamming includes but is not limited to, trying to sell products, trying to solicit traffic for your own blog, trying to solicit traffic for other commercial entities, etc. Do not post links to your own site unless they are directly relevant and even then, use sparingly.
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whats the question?
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Here's a game: let's see how long it's going to be before Orca gets banned for spamming the main blog with his own silly blog...
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Quoting GeoffreyWPB:
Easy one....

img src="Photobucket" alt="" />


Just a few more hrs over the bahamas and southeast florida would have had a major on there hands.
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I found another one but you all gotta answer H2009's question firstest!
Member Since: November 24, 2005 Posts: 635 Comments: 26685
A lot of people forget Katrina crossed Fla. first before she devestated the Gulf Coast.
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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