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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This is our current rain "blob".
Member Since: Posts: Comments:
Sounds like a bees nest at USA vs Spain Soccer match
Member Since: July 7, 2005 Posts: 0 Comments: 5417
1074. Ossqss
Quoting StSimonsIslandGAGuy:
OssGSS I would not be liking that at all! The parasailing company really should be more responsible.


Just watched the poor kids on the tube. 3 hr duration from an expected 15 minutes.

The storms blew up off shore and exhausted towards the beach. Who saw that coming?

Note to self-- cross off parasailing from the to-do list, Yikes -- L8R
Member Since: June 12, 2005 Posts: 6 Comments: 8188
Think I'll shut down for a while. Storm's moving overhead, and last time that happened a lightning strike took out my modem and my RJ45 / ethernet jack.

Later!
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well look at this new tropical wave
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1071. GatorWX
SEC owns NCAA sports!!!!!!!!! WOOHOO, not that I'm a Tiger fan, but I'll always be routing for an SEC team especially over a big 10 or ACC team. Good job boys.
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Raining w/ Thunder/lightning here right now.
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Quoting Ossqss:


When did we have them both negative prior? Does this relate to the transition to El Nino?

Just curious.
Sorry. Thinking abt PDO / NAO rather than AO. NAO & AO should oscillate together, from what I recall.
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1067. Ossqss
Interesting, stuck in the air due to an off shore Tstorm impact!

Parasailers safe after getting stuck in the air
Member Since: June 12, 2005 Posts: 6 Comments: 8188
Well good for LSU :-)...I take this as a good sign that the weather is behaving itself if this is taking the front line here.
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We are in desperate need of Blob.. any Blob.. even a small Blob....
Member Since: October 1, 2007 Posts: 81 Comments: 26516
1061. Patrap
LSU Defeats Texas in Omaha and are the National Champions of Collegiate Baseball 2009

11 to 4

Congratulations LSU Tigers




Member Since: July 3, 2005 Posts: 428 Comments: 129844
Congrats LSU on winning the World Series!
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Quoting Levi32:


Well first we need a blob lol. I'm only mentioning the possibility of troublesome stuff stirring up in the GOM over the next few days. However most features will be drifting slowly generally towards the SW away from the north gulf coast.


Thank you, Levi32 !! My anxiety level is now back within normal range ... for hurricane season.
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1055. JRRP
Quoting HURRICANECAT5:
IS THE WAVE COMING OFF AFRICA THE ONE THE GFS IS PICKING UP?

nop when this activity reaches the atlantic may be that it weakens a bit
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1054. Ossqss
Quoting BahaHurican:
It has been a while since we've had both negative at the same time. Wonder if we will see more recurving as a result. Or if this is the year for the NJ / NY strike scenario.

Need time to review historical maps again.


When did we have them both negative prior? Does this relate to the transition to El Nino?

Just curious.
Member Since: June 12, 2005 Posts: 6 Comments: 8188
Quoting Levi32:


True but it's not that unusual when you consider that the pattern is very amplified right now with a negative NAO and AO. Lots of north-south movement of the air instead of west-east.
It has been a while since we've had both negative at the same time. Wonder if we will see more recurving as a result. Or if this is the year for the NJ / NY strike scenario.

Need time to review historical maps again.
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Blog Update
Reflector site for those at work, which now also includes Weather456, daily updates


AOI #1

AOI #2

Member Since: October 1, 2007 Posts: 81 Comments: 26516
1050. KEEPEROFTHEGATE (Mod)






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1049. Levi32
Quoting HURRICANECAT5:
IS THE WAVE COMING OFF AFRICA THE ONE THE GFS IS PICKING UP?


No, the one the GFS develops is still over Africa at around 5W.
Member Since: November 24, 2005 Posts: 635 Comments: 26700
IS THE WAVE COMING OFF AFRICA THE ONE THE GFS IS PICKING UP?
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1047. Ossqss
Quoting stillwaiting:
ossgs:I got the edge of the wx as it was dying out as it moved south into sarasota...still one heck of a lightning storm!!!!,my friend lives near university and 75 and his power was out last night from 1-8am!!!!


It was kickin here. I would bet we had 60-70mph winds min. It moved my portable, 400 lb B-ball hoop and tossed everything in the yard around. I am one exit north and power was out but not sure how long. I was watching the backs of my eyelids :)
Member Since: June 12, 2005 Posts: 6 Comments: 8188
1026. Drakoen 9:59 PM EDT on June 24, 2009
Quoting hurricane23:


50kt shear no chance.


Yea. We are going to be looking at a late start season. I think we may have to wait till the late July or even early August.


We need a storm heading for Florida ASAP to get help Drakeon's get rid of his depression.
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1045. Levi32
Quoting BahaHurican:
Yep. Usually this time of year rainy weather systems impacting SFL/Keys/Antilles/Bahamas are more likely to be Twaves than fronts.


True but it's not that unusual when you consider that the pattern is very amplified right now with a negative NAO and AO. Lots of north-south movement of the air instead of west-east.
Member Since: November 24, 2005 Posts: 635 Comments: 26700
1044. Levi32
Quoting emeraldcoast:


He got my attention. Who dat blob gonna be ?
Native New Orleans girl now living in Florida panhandle ... wondering where dat blob gonna go ?


Well first we need a blob lol. I'm only mentioning the possibility of troublesome stuff stirring up in the GOM over the next few days. However most features will be drifting slowly generally towards the SW away from the north gulf coast.
Member Since: November 24, 2005 Posts: 635 Comments: 26700
ossgs:I got the edge of the wx as it was dying out as it moved south into sarasota...still one heck of a lightning storm!!!!,my friend lives near university and 75 and his power was out last night from 1-8am!!!!
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Quoting Levi32:


Well south of about 32N it ceases to be a true front, and is only a trough from then on. ....... The moisture in your image is basically bounding the upper trough, and it's not unusual to see them that far south at this time of year. That's why trough-splits are a problem in the early and late hurricane season.
This kind of setup is not THAT usual in mid-June. More of a May feature.
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Quoting naplesdreamer28:
Patrap - Trying to start a riot in here by showing a blob starting in the GOM? LOL


He got my attention. Who dat blob gonna be ?
Native New Orleans girl now living in Florida panhandle ... wondering where dat blob gonna go ?
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Quoting Ossqss:
Is it not unusual to have a frontal system push this far south this time of year?

It almost looks like winter.

Yep. Usually this time of year rainy weather systems impacting SFL/Keys/Antilles/Bahamas are more likely to be Twaves than fronts.
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1038. Levi32
Quoting Ossqss:
Is it not unusual to have a frontal system push this far south this time of year?

It almost looks like winter.



Well south of about 32N it ceases to be a true front, and is only a trough from then on. There is no big differences in temperature on either side of the front since the low-pressure system has been sitting there for so long and weakened considerably. The moisture in your image is basically bounding the upper trough, and it's not unusual to see them that far south at this time of year. That's why trough-splits are a problem in the early and late hurricane season.
Member Since: November 24, 2005 Posts: 635 Comments: 26700
nrt:thanks a bunch we'll have to see if the wx is clear,if so I'll snap a picture or 2 w/my phone and post them on my blog!!!
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TROPICAL DISCUSSION - INTERNATIONAL DESKS

...BUT...EARLY IN THE CYCLE...A LOW IS TO FORM JUST NORTH OF WESTERN CUBA OVER THE GULF OF MEXICO...WITH CLOSED CIRCULATION TO DRIFT SOUTHWEST TO THE NORTHERN YUCATAN THROUGH 48 HRS...AND MEANDER OVER THE CAMPECHE SOUND BY 72 HRS.
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1035. JRRP
Quoting hurricane2009:


Hey if USA can beat Spain in soccer anything is possible lmao

lol
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1034. Ossqss
Is it not unusual to have a frontal system push this far south this time of year?

It almost looks like winter.

Member Since: June 12, 2005 Posts: 6 Comments: 8188
1033. Levi32
Quoting hurricane2009:


Hey if USA can beat Spain in soccer anything is possible lmao


LOL
Member Since: November 24, 2005 Posts: 635 Comments: 26700
1031. Levi32
Quoting hurricane23:


50kt shear no chance.


TUTT lifts out in 4-6 days. The upper-level environment will be marginal.
Member Since: November 24, 2005 Posts: 635 Comments: 26700
1030. Levi32


This is the set-up for our trough-split that is beginning now and will complete within 48 hours. The frontal trough and associated area of weak low pressure near the NE gulf coast are going to be sitting in the same area for a few days as the upper flow gets split and an upper feature starts backing to the SW. Situations like this always, always have to be watched for mischief no matter what, as the convergence caused by the surface trough combined with the upper feature can cause cyclogenesis. In 3-4 days energy from the tropical wave that will be moving into the NW Caribbean will get piled into the area as well.

There may be nothing on the models right now, but they rarely pick-up on home-brew developments until they're right on top of them. What they are showing is the moisture that will be lingering in the area over the next several days, and this area should be watched. Troughs in the Gulf of Mexico always mean trouble when they start sitting around, even if nothing substantial organizes.
Member Since: November 24, 2005 Posts: 635 Comments: 26700
1029. KEEPEROFTHEGATE (Mod)
Quoting Drakoen:


Yea. We are going to be looking at a late start season. I think we may have to wait till the late July or even early August.
maybe not till october
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Quoting Drakoen:


Yea. We are going to be looking at a late start season. I think we may have to wait till the late July or even early August.
Feels right.

I think those Eward moving troughs will have 2 cool it before we see anything serious.
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1027. KEEPEROFTHEGATE (Mod)


ATLANTIC BASIN
AOI
10N/10W
AOI
11N/56W
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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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