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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weather456 do you think us in cayman would get something
soon around the 1-15
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Does anyone have a link to the recent MJO Forcast?
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Quoting hurricane2009:


What are your thoughts on this system 456?


It's been discuss in my blog, but I describe it is as odd.
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NCSU has put out this 2009 Hurricane Forcast:

"News Release

2009 Hurricane Season Should Contain No Surprises, NC State Researchers Say
Media Contact(s)

Tracey Peake, News Services, (919) 515-6142

FOR IMMEDIATE RELEASE

Researchers at North Carolina State University believe that 2009 will bring a near-normal hurricane season, with storm activity in the Atlantic basin and the Gulf of Mexico slightly above the averages of past 50 years, but staying in line with those from the past 20 years.

According to Dr. Lian Xie, professor of marine, earth and atmospheric sciences, and collaborators Dr. Montserrat Fuentes, professor of statistics, and graduate student Danny Modlin, 2009 should see 11 to 14 named storms forming in the Atlantic basin, which includes the entire Atlantic Ocean, the Gulf of Mexico and the Caribbean Sea.

Of those named storms, six to eight may grow strong enough to become hurricanes, and there is a 45 percent chance that one of those storms will make landfall along the coast of the southeastern United States as a hurricane.

As for the Gulf, Xie's data indicate the likelihood of three to five named storms forming, of which one to three will become hurricanes. The researchers expect two to four named storms to make landfall along the Gulf, and there is a 70 percent chance that at least one of those storms will be of hurricane status.

"The data show that the number of storms this year will not vary significantly from those of the past 20 years; in fact, 2009's numbers are slightly lower than last year's prediction of 13 to 15 named storms," Xie says.

Xie's methodology evaluates data from the last 100 years on Atlantic Ocean hurricane positions and intensity, as well as other variables including weather patterns and sea surface temperatures, in order to predict how many storms will form and where they will make landfall.
The Atlantic hurricane season runs from June 1 through Nov. 30."

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Quoting KEEPEROFTHEGATE:
july 10th

i'm ok with that
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I am not asking for a hurricane or at the most a weak cat 1
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This time Thursday:

Tropical wave analysed along 11W south of 13N with a 1011 mb low along the axis at 10N.
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Quoting wunderkidcayman:
hi guys please tell me we might get a storm soon
july 10th
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Quoting hurricane2009:


are you that bored?

Nope no storms til 2014 lol

a lot more that you think
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The USA men's soccer team just pulled off one of the biggest upsets ever! They have beaten the #1 team in the world Spain! The USA held off the dangerous offense of Spain through the entire match, and came out on top in the end! Nobody thought the USA could do it but that's why so many love soccer because... Anything can happen!
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hi guys please tell me we might get a storm soon
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We actually had a good soaking rain yesterday here in Pensacola. It stormed consistently for a few hours. Some of the storms were even bordering on severe.
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Been Watching a little area of convection trying to spring up off the Nicaraguan coast, shear ain't that high in that area from what I can tell, might be interesting to watch later.
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Quoting atmoaggie:
Yay, we got rain in SE LA (northshore of Lake P)...careful what you wish for...

Neighborhoods without power, wife and kids hiding in bath tub, wires down in yard, etc.

Terrific CAPE all over once the cap is broken.

L8R.

That is what is driving me nuts. Aside from the cap, this heat is perfect for some fantastic rain. But nothing can crack 8-10k ft.
Member Since: August 3, 2008 Posts: 16 Comments: 5875
Oh, Patrap. I will have to get ya lunch another time. I ended up getting taken out myself by the lawyers down by Carondelet and Gravier. They are the client, so "no thanks" really wasn't an option.

I did see a couple of people-sized puddles with sunglasses and cell phones while I was down there. Ya think .... likely melted tourists?
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Yay, we got rain in SE LA (northshore of Lake P)...careful what you wish for...

Neighborhoods without power, wife and kids hiding in bath tub, wires down in yard, etc.

Terrific CAPE all over once the cap is broken.

L8R.
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Quoting hurricane2009:


Was that the amount of time you predicted before the next post? LOL if so YOU LOSE LMAO


Start of the LSU/Texas game. I stink at that too...LOL
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AOI #1

AOI #2


Not sure if my little BLOB is disappearing.. or heading west?
Member Since: October 1, 2007 Posts: 81 Comments: 26511
Quoting captainhunter:
869. jeffs713

Don't forget us in Panama City Beach. We need rain desperately. My sprinklers can't keep up.


Storm on radar to your North trying to push south but struggling. The storms are scattered to say the least in the Panhandle today, it rained at my house 3 miles from where I work but not a drop at work! I'm out for today, stay cool everyone!
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1 hour and 42 minutes.....
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Oh, I see, Levi.
Stormpetrol, I agree.
This is the time of year when those little buggers can squeeze through the shear and blow up from nothing. And there are lot of little black darts in that Quickscat... (layman's terms...ha!)
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I was standing out front waiting for that ice cream truck.....but.....

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Tropical Tidbit for June 24
Member Since: November 24, 2005 Posts: 635 Comments: 26564
Quoting StormSurgeon:
Sorry folks, this is the last time, I don't promise....


...
This makes Chinese Water Torture look like a cakewalk.
Member Since: August 3, 2008 Posts: 16 Comments: 5875
Member Since: November 24, 2005 Posts: 635 Comments: 26564
SAL 5-day JAVA loop
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Quoting Chicklit:


I don't see any dust...


It's more than it looks....for some reason the SSD site set the Meteosat imagery color scale up a few notches than all the other imagery. The blacks in that image are actually oranges in the ones you typically see, whites are greys....etc.
Member Since: November 24, 2005 Posts: 635 Comments: 26564
Quoting hurricane2009:


Shear is still 30 knots though in the area it is going, lets see if shear can drop to say 20 and they will see.


TRue , but shear appears to be lessening even compared to yesterday in that area, The W Caribbean seems more favorable shear wise and there is plenty moisture in its path for now.
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I don't see any dust...
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Sorry folks, this is the last time, I don't promise....

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Quoting captainhunter:
869. jeffs713

Don't forget us in Panama City Beach. We need rain desperately. My sprinklers can't keep up.


My bad... I'm just going to update the post to "the Big Bend area of FL"
Member Since: August 3, 2008 Posts: 16 Comments: 5875
Quoting extreme236:


I understand that there is also supposed to be some trof-split in the Gulf that could stir up something during the next couple days.


Yes, as the east coast trough lifts out during the next 3 days it will split and leave a piece behind that will slowly back SW over the Gulf of Mexico. With the old frontal trough sitting in there causing an area of converging winds it is a situation that should be watched for mischief.
Member Since: November 24, 2005 Posts: 635 Comments: 26564
Quoting Chicklit:
That's the one we're talking about stormpetrol.


Shear seems to have dropped quite a bit in that area and the W Caribbean compared to a few days ago, with July approaching these areas climatology speaking gets slightly more favorable.
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LOL ban??? hmmm


Link
Member Since: May 21, 2006 Posts: 5091 Comments: 114776
That's the one we're talking about stormpetrol.
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Interestingly enough, a strong wave to emerge off the African coast in a few days. Probably nothing to be concerned of development wise but after last year I'm watching it.
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Interesting tropical wave approaching the Windwards in a day or 2
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869. jeffs713

Don't forget us in Panama City Beach. We need rain desperately. My sprinklers can't keep up.
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Quoting hurricane2009:


Yea but I believe it was Levi who said that this wave could factor into whatever will try to develop in the GOM or West Caribbean. It is possible that this wave could be the added moisture surge needed


I understand that there is also supposed to be some trof-split in the Gulf that could stir up something during the next couple days.
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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.