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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1119...
Can't say I didn't warn ya'll....

35. ajcamsmom2 11:41 AM CDT on June 23, 2009
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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1125. Levi32
Quoting hurricane2009:
We had a debate last year, oh the GFS was showing it but it doesnt matter much blah blah blah, some who were in agreeing with the GFS brought up how the GFS nailed both Dean and Felix in 2007 2 weeks in advance.

It is only June yes, but still to me the GFS does a better job on tropical wave development in the Atlantic than it does figuring out how the home grown stuff develops


I agree.
Member Since: November 24, 2005 Posts: 635 Comments: 26681
Quoting hurricane2009:


Look at posts 1093, 1095 and 1097 posted by Keeper.

thanks.
Member Since: July 11, 2006 Posts: 14 Comments: 11385
1122. GBguy88
Quoting SavannahStorm:
A haiku:


a change I feel
the models show the path
black skies loom



A haiku follows a 5-7-5 syllable pattern, but you get credit for creativity :P
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1121. JRRP
Member Since: August 16, 2007 Posts: 0 Comments: 6155
Quoting melwerle:
Is Doc Masters still on vaca? That would be the sign!

Yep he comes back on the 29th!
Member Since: Posts: Comments:
Is Doc Masters still on vaca? That would be the sign!
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1118. KEEPEROFTHEGATE (Mod)
cloud top temps are -90c in that blob rolling off very high
Member Since: July 15, 2006 Posts: 175 Comments: 54827
1117. Levi32
Quoting Chicklit:
Hello, Levi and Hurricane09.
What are you referring to?


This wave over western Africa that the GFS develops in the eastern Atlantic in a couple days:



And I'm also monitoring this mid-level circulation near Costa Rica that will be moving NNW over the next few days and could get into the Gulf of Mexico.

Member Since: November 24, 2005 Posts: 635 Comments: 26681
Hurricane - time to turn off the a/c and sit with ceiling fans in that case. I'm all over it.
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Quoting Levi32:


Evening Mel. Yeah I'm sweltering in 47 degrees right now. I don't think I can take anymore =D


Oh Levi - I was going to say something that was going to get me banned. ;)

I'm so jealous but heading out and i hear it was in the sixties in the morning at my new home. Just worried about the drive there. No weather there....
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The 00Z run is keeping our CV AOI as a closed low, the few runs before that kept swinging it between a closed and open wave.
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Hello, Levi and Hurricane09.
What are you referring to?
Member Since: July 11, 2006 Posts: 14 Comments: 11385
1111. Levi32
Quoting hurricane2009:


Lvei looks to me that the GFS is developing the AOI that Keeper is showing too


Yup has been for 4 straight runs now or something like that.
Member Since: November 24, 2005 Posts: 635 Comments: 26681
1109. Patrap
Sea Level Rise Impacts on Florida and Miami

Music by Brian Fisher and Slow Motion Crash
Narrator: Susan Glickman
Director/Editor: Video Rahim
Executive Producer: Stephen Smith

Member Since: July 3, 2005 Posts: 426 Comments: 129089
1108. Levi32
Big wave there....I'm not discounting the GFS on this one. This wave has the potential and the environment to work with.
Member Since: November 24, 2005 Posts: 635 Comments: 26681
1107. JRRP
this is the first time of the season that i see 3 TW
Member Since: August 16, 2007 Posts: 0 Comments: 6155
A haiku:


a change I feel
the models show the path
black skies loom
Member Since: Posts: Comments:
Member Since: July 11, 2006 Posts: 14 Comments: 11385
Shear's dropping. There's no strong El Nino blowing everything apart. And we've just had a blast of warm air. So guess what.
Something's going to develop.
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1102. KEEPEROFTHEGATE (Mod)
AOI
mark
11n/10w
Member Since: July 15, 2006 Posts: 175 Comments: 54827
1101. Levi32
0z GFS 96 hours....circulation moves NW into the NE Bay of Campeche under favorable upper-level winds.

Member Since: November 24, 2005 Posts: 635 Comments: 26681
1100. KEEPEROFTHEGATE (Mod)
yes its a AOI worth the watch
Member Since: July 15, 2006 Posts: 175 Comments: 54827
Quoting hurricane2009:


I also think many fail to realize that even in the heart of the season, how many of these systems that form in the GOM and Caribbean are from a combination of things coming together at the right time.

This kind of development where we have the trough split, plus that mid-level low and maybe even that tropical wave moving into the islands, all combining together at the right time. It can happen, and happens more often than many think.



Once you get towards the start of July one should expect to see a uptick in tropical formation regardless how busy or slow it was in June, even if a storm does not form it is highly unlikely there will be no areas of interest for July.
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1097. KEEPEROFTHEGATE (Mod)
Member Since: July 15, 2006 Posts: 175 Comments: 54827
1096. Levi32
Quoting hurricane2009:


I also think many fail to realize that even in the heart of the season, how many of these systems that form in the GOM and Caribbean are from a combination of things coming together at the right time.

This kind of development where we have the trough split, plus that mid-level low and maybe even that tropical wave moving into the islands, all combining together at the right time. It can happen, and happens more often than many think.


Yeah and I don't want to be all puffed up here or anything but I've been talking for 3 weeks now about moisture advecting northward into the western Caribbean and Bay of Campeche around this time between the 20th and 30th of June, and sure enough we had the BOC disturbance a couple days ago that came up across Mexico from the EPAC, and now this mid-level circulation coming into the Caribbean. Even if nothing develops you can see the pattern that has evolved where we can get disturbances in this area.
Member Since: November 24, 2005 Posts: 635 Comments: 26681
1095. KEEPEROFTHEGATE (Mod)
Member Since: July 15, 2006 Posts: 175 Comments: 54827
1093. KEEPEROFTHEGATE (Mod)
Member Since: July 15, 2006 Posts: 175 Comments: 54827
Member Since: July 11, 2006 Posts: 14 Comments: 11385
1091. Levi32
Quoting hurricane2009:
well we got a few models hinting it Levi, but you know someone will come on and say...

Its the NAM, dont use it for tropical systems and the GFS has been terrible this year, I guarantee no storms til the end of next month.....

then we set it in stone and disappear for 3 weeks lol


Well I don't care lol. I didn't even notice the models did something with it until I spotted it on satellite and decided to take a look. Even if they weren't showing anything significant I still say keep a close eye on it. These things have a funny way of causing trouble when least expected.
Member Since: November 24, 2005 Posts: 635 Comments: 26681
1089. Levi32
Quoting melwerle:
Good Evening Everyone - hope everyone isn't dying from the heat tonight...we've had balmy 95 degree afternoons here.


Evening Mel. Yeah I'm sweltering in 47 degrees right now. I don't think I can take anymore =D
Member Since: November 24, 2005 Posts: 635 Comments: 26681
1087. Levi32
0z GFS 54 hours shows a closed low forming north of the Honduras coast from the mid-level circulation I mentioned above. Also notice in the eastern Atlantic still developing that wave.

Member Since: November 24, 2005 Posts: 635 Comments: 26681
Looks like things are setting up for tropical storm genesis. Nothing we can do but observe.
Member Since: July 11, 2006 Posts: 14 Comments: 11385
Good Evening Everyone - hope everyone isn't dying from the heat tonight...we've had balmy 95 degree afternoons here.
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1084. Levi32
Quoting wunderkidcayman:

not just that the 00z nam from ncep




Lol what do ya know....I've got support from the NAM. *cough*

0z GFS shows the mid-level circulation and associated moisture moving north of Honduras in 42 hours:

Member Since: November 24, 2005 Posts: 635 Comments: 26681
Quoting Levi32:
Another thing that I would watch closely is this mid-level circulation near Costa Rica that will be moving up through Nicaragua and Honduras tomorrow and Friday. From there it will probably get pulled NNW over the extreme western Caribbean and in the vicinity of the Yucatan in 3-4 days by the trough split in the Gulf of Mexico backing southwest into the Bay of Campeche. This is another area of energy that will be added to the mix at roughly the same time as the tropical wave. This whole area needs to be watched.


not just that the 00z nam from ncep


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1081. Levi32
Quoting hurricane2009:


LOL yea it does, oh and one more thing...

GOOOOOOOAAAAAAALLLLLLLLLLLLLLL!!!!!


That was an awesome goal. I'm not used to seeing a soccer game with this many shot opportunities. The last one I saw was really boring but I'm loving this game so far.

And ugh my little brothers are going to watch looney tunes now so I can't see it lol.
Member Since: November 24, 2005 Posts: 635 Comments: 26681
Congrats to LSU...too bad for Texas.
Link
Interesting NHC 8:05 Discussion for those who haven't seen it.
Member Since: July 11, 2006 Posts: 14 Comments: 11385
1078. Levi32
Another thing that I would watch closely is this mid-level circulation near Costa Rica that will be moving up through Nicaragua and Honduras tomorrow and Friday. From there it will probably get pulled NNW over the extreme western Caribbean and in the vicinity of the Yucatan in 3-4 days by the trough split in the Gulf of Mexico backing southwest into the Bay of Campeche. This is another area of energy that will be added to the mix at roughly the same time as the tropical wave in the eastern Caribbean. This whole area from the NW Caribbean to the Gulf of Mexico needs to be watched.

Member Since: November 24, 2005 Posts: 635 Comments: 26681

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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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