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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What the GFS is forecasting is garbage. The GFS has had a poor cyclogenesis record this year and none of the reliable computer forecast models show development.
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76. WAHA
Quoting hurricane2009:


dust moves on like anything else, that dust wont be there at the time the GFS has this storm developing

Oh, you mean that beastly huge thing over Sudan?
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75. JRRP
but the gfs have had problems this season
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Quoting hurricane2009:


So you think it is actually possible that we could see a CV type storm this early?



Remember Bertha I guess it is possible!
Member Since: July 7, 2005 Posts: 0 Comments: 5282
71. WAHA
Quoting WPBHurricane05:
Post 21.-- wow!! The GFS is forecasting a Cape Verde storm....

All I see is dust. Look at the RGB map.
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Quoting Weather456:
For those who think the GFS is joking with the cape verde system, look at the conditions between next Monday and next Friday.


I told you there was a beast to the east :)

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Quoting antonio28:


Agree with that! Levi shear forescast for that time frame support tropical development. Do anyone rember Bertha!


It definitely bears watching. This is the first time this year conditions will be even marginally favorable in the tropical Atlantic.
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Quoting Weather456:
For those who think the GFS is joking with the cape verde system, look at the conditions between next Monday and next Friday.

Look at the last images I posted...#60... maybe that on the far right is what might be it hinting at.
Goodnight
Member Since: September 30, 2007 Posts: 9 Comments: 15935
Quoting Orcasystems:


I see your little buddy burped again :)


Nah lol that was a tectonic earthquake felt by the seismograph. It was not related to the volcano. I guess it didn't wake her....she's a deep sleeper :)
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Quoting Levi32:


Well at least the TUTT will have pulled out of the eastern Atlantic by that time. That wave will have much more breathing room than any of its predecessors.


Agree with that! Levi shear forescast for that time frame support tropical development. Do anyone rember Bertha!
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I think the GFS is spinning up a blob of dust, since the spot it shows the "storm" is also about where the current wave pulling off of Africa would be at that time... which happens to be right in the middle of a SAL cloud.
Member Since: August 3, 2008 Posts: 16 Comments: 5880
I'm out...it's getting to cold.
Goodnight all.
Cheers AussieStorm
Member Since: September 30, 2007 Posts: 9 Comments: 15935
For those who think the GFS is joking with the cape verde system, look at the conditions between next Monday and next Friday.
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Quoting Levi32:
NASA high-resolution visible satellite loop of Andres and the Bay of Campeche

Andres' low-level circulation is actually becoming exposed now...convection has waned drastically. I don't think there's going to be any coming back from this one.


I see your little buddy burped again :)
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Member Since: September 30, 2007 Posts: 9 Comments: 15935
59. WAHA
Quoting WPBHurricane05:
Post 21.-- wow!! The GFS is forecasting a Cape Verde storm....

Are you kidding? Okay, I'll check right now.
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Welcome showers hopefully

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Member Since: September 30, 2007 Posts: 9 Comments: 15935
NASA high-resolution visible satellite loop of Andres and the Bay of Campeche

Andres' low-level circulation is actually becoming exposed now...convection has waned drastically. I don't think there's going to be any coming back from this one.
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Tropical Update
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Quoting CaneWarning:
What is that blob off the west coast of Florida that is showing up on those maps?


A very elongated surface trough of low pressure that arised from an old frontal boundary.

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Member Since: September 30, 2007 Posts: 9 Comments: 15935
Blog Update
Reflector site for those at work, which now also includes Weather456, daily updates


AOI #1

AOI #2
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An undersea earthquake with a magnitude of 6.7 struck off the remote New Ireland area of Papua New Guinea on Wednesday, triggering a local tsunami warning, US scientists said.

IRIS Seismic Monitor
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What is that blob off the west coast of Florida that is showing up on those maps?
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Quoting jeffs713:

Where did you find that wind shear map?


WU model page
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48. JRRP
Quoting AussieStorm:


Africa is free of clouds
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Current SAL
Member Since: September 30, 2007 Posts: 9 Comments: 15935
Quoting Weather456:


200 mb winds not equal wind shear






Where did you find that wind shear map?
Member Since: August 3, 2008 Posts: 16 Comments: 5880
Quoting Weather456:


200 mb winds not equal wind shear






Member Since: September 30, 2007 Posts: 9 Comments: 15935
Levi - thank you for this report!

Quoting Levi32:
Good morning all.

Tropical Tidbit for Tuesday June 23 with Video
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43. JRRP
Quoting Weather456:


200 mb winds not equal wind shear






thanks
i did not know that
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Pretty dead over there also... mind you to the east of this picture.. there is a big one brewing.
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Quoting JRRP:
but will have a lot of wind shear


200 mb winds not equal wind shear





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Quoting JRRP:



Member Since: September 30, 2007 Posts: 9 Comments: 15935
Quoting Chicklit:
Nice job with the Tropic Tidbit Blog Levi.



Thanks =)
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deleted
Member Since: September 30, 2007 Posts: 9 Comments: 15935
Quoting JRRP:
but will have a lot of wind shear


Well at least the TUTT will have pulled out of the eastern Atlantic by that time. That wave will have much more breathing room than any of its predecessors.
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Nice job with the Tropic Tidbit Blog Levi.

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Oh NO!!! Dr. Masters is on vacation...Last year that meant all h--l was about to break out...Get your life preservers ready...lol
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34. JRRP
but will have a lot of wind shear
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Hurricane Hunter
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hear on the blog nothing to whatever date dont know how anyone can predict that. who knows whats going to happen two wks from now.


I can't tell you whether it will snow on Christmas Day in 2050. But I can tell you that it'll be colder on Christmas Day, 2050 than it was on July 4th, 2050.

Specifics are not predictable out beyond a week or two. Trends are.
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31. IKE
12Z GFS also showing a good deal of rain over the lower SE USA the next week.

Keep an eye on the SE GOM in a few days....
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Good Afternoon

Andres Update
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29. JRRP
Quoting WPBHurricane05:
Post 21.-- wow!! The GFS is forecasting a Cape Verde storm....


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Member Since: September 30, 2007 Posts: 9 Comments: 15935
27. IKE
Quoting WPBHurricane05:
Andres...another epac dud??


It's on it's way to being finished...
Member Since: June 9, 2005 Posts: 23 Comments: 37858

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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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