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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Quoting RMM34667:
cool picture from cape cod..

In Chatham, an austere utopia yields to a relentless tide


Link


That pic is just way too cool! I love those shots at wave level! :)
Member Since: August 26, 2006 Posts: 10 Comments: 3617
The flip side of the evacuation argument is that it only takes just one.

We use to have to prepare a lot more for storms before they were able to track as well as they can now. Our theory then, and still is today, is better to be wrong 9 times, and right once. We put our seat belts on every time we get in the car in case we have an accident - how often does it actually happen?

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Hi Kman:

would just fit the pattern of no real pattern at all!
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A tropical wave off Africa does not have to develop into a full storm tracking across the Atlantic, some times all you need is the leftover energy from a wave that dissolved to cause trouble once it does get into the areas that are conducive for development.

But really, guys, no one is right or wrong, and everyone can have an opinion. So play nice.
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Wouldn't it be ironic if the NAM, which everyone says should be ignored for the tropics, is really on to something ??

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Certainly Impressive...
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Quoting Orcasystems:


Nothing like 100 weather and a garbage strike.. I hope it doesn't last more then a month or two :)
Talk about putting up a stink - Yikes! When the strike is over - wont't the workers be stuck cleaning up all that mess. They must be striking for a considerable change in the current status, to be willing to face that hell.

KOTG, when do you expect a reprieve from the heat?
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Quoting Ossqss:
This seems appropriate. Maybe


Nice one! Lol.
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Quoting stillwaiting:
scott is definately not a troll,extreme,as a matter of fact I believe he's a met!!!,some people on the board do "hypecast",but I haven't seen that on here so far this season,STORMTOP does come to my mind though,lol:)


lol yeah I'm sure...a met wouldn't come onto a forum and cause trouble
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1313. Tazbeat
Quoting scottsvb:



Alot of noobys that browse these forums think that most know what they're talking about.. but really 98% or more in here dont. There are a couple good forecasters/or peeps with degrees in here..but more METs dont use these forums cause for 1.... we get brushed aside by the massive amount of spam (hypecasters/wishcasters) and they never fully learn. INFACT... I have stated many times about certain things not to worry about and people just dont read or the kids-novice keep scaring up dream situations on what fantasy might happen.

Again there are a few good peeps in here and some that are learning and dont overhype or care to discuss something (cause they know).. but the whole problem is people who browse these sites dont know who really knows what their talking about.



First of all, I would suggest that there may be a bit more than 2% of the people posting in here who actually know what they're talking about.

But if you want to talk hype, let's talk the mainstream sources of information. One of my big problems has always been with bogus storm surge maps showing who will be underwater during which category of storm. When in reality, the storm surge wouldn't get anywhere close to those projections. Another thing is building up storms to be bigger and worse then they truly are, to try to convince people to leave a particular area. And yes, I know the consequences of not doing this, I live in SW FL and am well aware of what Charley did at the last minute. But if people are told a storm will be bad, and they need to evacuate, and they do, then the storm isn't bad, what are the chances of that person evacuating the next time a storm comes through? The mainstream outlets need to not hype the storms - just tell the truth. Why do you think I come here and not to the weather channel for info?
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Quoting RMM34667:
cool picture from cape cod..

In Chatham, an austere utopia yields to a relentless tide


Link




WOW!!!!
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1311. Ossqss
This seems appropriate. Maybe
Member Since: June 12, 2005 Posts: 6 Comments: 8185
scott is definately not a troll,extreme,as a matter of fact I believe he's a met!!!,some people on the board do "hypecast",but I haven't seen that on here so far this season,STORMTOP does come to my mind though,lol:)
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cool picture from cape cod..

In Chatham, an austere utopia yields to a relentless tide


Link
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Quoting jeffs713:

I think I define "wishcasting" differently. I define it as sticking to something developing when it is highly unlikely to develop, based on current conditions.


Which by that definition, you cannot say it's wishcasting
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1281.
Scott doesn't that happen though everyday with the news and local weather I went to work and people talked about the lightning storm that occurred at 5am in the morning, that was not in a blog, I have not heard anyone say a hurricane will hit because Dr.M's blog said so.I suppose someone could say that, but a savvy person would check their weather station for that.

Your right there some great bloggers on here (456, StormW) are both watching these areas so it must have some chance.
Member Since: July 7, 2005 Posts: 0 Comments: 5152
I guess this an example of hype then lol.


INITIAL 04/0900Z 22.7N 55.8W 125 KT
12HR VT 04/1800Z 23.5N 57.7W 125 KT
24HR VT 05/0600Z 24.0N 60.2W 115 KT
36HR VT 05/1800Z 24.0N 62.6W 110 KT
48HR VT 06/0600Z 23.4N 64.9W 110 KT
72HR VT 07/0600Z 22.5N 69.5W 115 KT
96HR VT 08/0600Z 23.0N 73.5W 115 KT
120HR VT 09/0600Z 25.0N 76.5W 115 KT


Better to be prepared than to wait and do nothing until right before the storm hits.
No one is saying they think 100% this will develop, I give it a 30-40% actually, because of the conditions and that we've seen so many waves go poof as soon as they hit the water.
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Quoting hurricane2009:


Not one person here has wishcasted anything about this tropical wave. Just because we talk about it doesnt mean we are freaking out about it

I guess to make others happy we should just not say a word about anything east of 60W until later July.

I think I define "wishcasting" differently. I define it as sticking to something developing when it is highly unlikely to develop, based on current conditions.
Member Since: August 3, 2008 Posts: 16 Comments: 5871
1297. Ossqss
Quoting scottsvb:



Cleveland will win a Championship before that happens..


LoL, the Browns did win when they moved to Baltimore :)
Member Since: June 12, 2005 Posts: 6 Comments: 8185
Quoting scottsvb:


LOL extreme!


lol you sure? Its going to get that way soon enough until it goes Poof... then everyone downplays their hype!


Your just a troll who wants to cause problems...we are all interested simply because Bertha formed at 25W last year, so it's happened before. No one is hyping anything/
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1295. beell
Couple of other things.
If you are are not making an attempt to follow each and every wave from Africa clear through to the EPAC, then you are not "watching" the tropics. W456 comes to mind...

There is almost as much to be learned by why something did NOT form.
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Quoting extreme236:
1281. No one is trying to scare anyone...wow what fantasy world are you in lol



LOL extreme!
Quoting extreme236:
1281. No one is trying to scare anyone...wow what fantasy world are you in lol

Quoting extreme236:
1281. No one is trying to scare anyone...wow what fantasy world are you in lol

Quoting extreme236:
1281. No one is trying to scare anyone...wow what fantasy world are you in lol




lol you sure? Its going to get that way soon enough until it goes Poof... then everyone downplays their hype!
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Thats a little ridiculous. Bloggers cant be told what to post based on how someone else might take it and run with it. Everyone has to be responsible for their own actions. If someone reads a post by one of the bloggers here instead of listening to the NHC or their own meteorologist then they have to take the responsiblity for that, no one else. Nothing wrong with blob watchin, IMO.
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Atleast there are some who are thinking positive no doubting that there will be a hurricane. that is not climatology.it is a truism
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hurricane 2009,you eat alot of breakfasts!!,lol;)
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Good morning.
It is 10:oo am, and the heat index is up to 96. It feels that way too.
Armpits are droolin'.
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SAL showing up pretty darn good on the atlantic visable loop
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1281. No one is trying to scare anyone...wow what fantasy world are you in lol

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Quoting sporteguy03:
Why are some bloggers so concerned what areas other bloggers watch? I find the insight on this blog of great value let em blog!



cause there are noobs that browse these forums.. you get some people that post and hype up something...then that noob that was reading this goes to work and tells everyone theres a hurricane forming... and I hear that all the time.

OR

Same thing,,, people hypecast and the noobys (people who just found this site) post or just read this get overly excited or scared thinking its coming to their house. Alot of noobys that browse these forums think that most know what they're talking about.. but really 98% or more in here dont. There are a couple good forecasters/or peeps with degrees in here..but more METs dont use these forums cause for 1.... we get brushed aside by the massive amount of spam (hypecasters/wishcasters) and they never fully learn. INFACT... I have stated many times about certain things not to worry about and people just dont read or the kids-novice keep scaring up dream situations on what fantasy might happen.

Again there are a few good peeps in here and some that are learning and dont overhype or care to discuss something (cause they know).. but the whole problem is people who browse these sites dont know who really knows what their talking about.
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Quoting stoormfury:
Climatolgy or no climatolgy. anything can happen when dealing with tropical meteorology. we have had numerous examples. Bertha of 2008 broke all the rules of climatology. nothing is cast in stone


What is cast in stone is that there will be a hurricane this year
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1279. beell
And just for the record, fwiw, put me in the "I'm gonna watch it anyway" camp.
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Climatolgy or no climatolgy. anything can happen when dealing with tropical meteorology. we have had numerous examples. Bertha of 2008 broke all the rules of climatology. nothing is cast in stone
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Quoting scottsvb:
bertha didnt form near 30W.... it was around 45W.. I could be wrong though... find a stat..Im too lazy to find it...lol!


Link
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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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