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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1177. GatorWX
in a while crocodile.....yeah, lol
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1176. Levi32
Alright Later Gator .....lol
Member Since: November 24, 2005 Posts: 635 Comments: 26652
1175. GatorWX
Alright Levi, probably see you on here tomorrow, what is it 10:15 there? Too late here in sw FL~!~ Off to bed, gotta work @ 0900, ouch!!!
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1174. GatorWX
I'm going to try to transfer my job (I work for the mighty uhaul). Keep in mind we have the right equipment @ the lowest cost guaranteed. And actually that's one of the things I really like about the job, we can look up competition rates, beat them and give the customer a really low rate and really wow them. Feels good you know. Uhaul really does own the moving business. Penske and Budget are trying, but Uhaul will always beat them price wise with better equipment.
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1173. Levi32
Quoting GatorWX:
Levi, any UHAUL centers in Homer? and how far up the coast is it?


Here's the Map of Homer's Location

Yes we have a UHAUL center on Ocean Drive near the carwash. At least I always see a bunch of them parked there lol.
Member Since: November 24, 2005 Posts: 635 Comments: 26652
1172. Levi32
Lol Gator. I think it must have been the crazy snowstorms for me. We've had the equivalent of Cat 2 hurricanes here in my early childhood. The first satellite image of a hurricane I ever saw was on TV of Hurricane Lili in 2002, and then Claudette in 2003. After those storms I started paying more and more attention to hurricanes.
Member Since: November 24, 2005 Posts: 635 Comments: 26652
1171. GatorWX
Levi, any UHAUL centers in Homer? and how far up the coast is it?
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1170. GatorWX
Perhaps it was this storm that ignited my interest, being that I was 6 months old...lol They say babies learn less as they grow, perhaps this was one of my first great experiences.
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1169. GatorWX
Gloria (according to my parents) passed right over our house in upstate NY, newburgh area to be exact.
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1168. Levi32
Night H2009
Member Since: November 24, 2005 Posts: 635 Comments: 26652
1166. Levi32
Quoting GatorWX:
That's right, I remember you speaking about Alaska and that you were from there the other day when everyone was whining about the heat in FL and posting their current conditions. I may be moving to AK after the summer. Not 100% sure yet, but it's a thought. Homer doesn't get exceptionally cold does it? Average lows/highs in winter 28/16 or thereabout?


That's pretty close Gator. Days of 20 below zero used to be fairly common here but in the last decade sub-zero temps have been rare.
Member Since: November 24, 2005 Posts: 635 Comments: 26652
1164. Levi32
I'm not really sure where my passion for weather came from. I've had it since I was a little kid. I started tracking storms in 2002. I'm hoping to maybe major in Meteorology when I go to college.
Member Since: November 24, 2005 Posts: 635 Comments: 26652
1163. GatorWX
did Gloria hit the NE?
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1162. GatorWX
That's right, I remember you speaking about Alaska and that you were from there the other day when everyone was whining about the heat in FL and posting their current conditions. I may be moving to AK after the summer. Not 100% sure yet, but it's a thought. Homer doesn't get exceptionally cold does it? Average lows/highs in winter 28/16 or thereabout?
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1160. GatorWX
Andrew is what first caught my eye as a kid, and ever since then I've been really fascinated by weather. I strongly thought about a meteorological career, but two classes pertaining to it during my community college tenure was about it. Charley's eye passed 11.5 nm sse of me, and since then I've been on this blog. I used to have a different name, but I think I got booted off for saying something "bad" about a certain female weather channel anchor.
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1159. Levi32
Homer, Alaska
Member Since: November 24, 2005 Posts: 635 Comments: 26652
1158. GatorWX
I've learned a lot on here and elsewhere on the internet and have read a lot of books too. Where are you from Levi?
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1157. Levi32
Quoting GatorWX:


I'm not real good @ understanding doppler info. I know plenty about the tropics and atmospheric conditions, but not tornados. I just know to look for the hook.


I'm not that great of a doppler analyst myself. I just know how to recognize the common signatures. Severe thunderstorms aren't my specialty. Like you, I'm best with the tropics.
Member Since: November 24, 2005 Posts: 635 Comments: 26652
1156. GatorWX
Quoting Levi32:


It's definitely rotating based on radial velocity. There is a strong possibility of either a tornado on the ground or the storm may produce one soon.



I'm not real good @ understanding doppler info. I know plenty about the tropics and atmospheric conditions, but not tornados. I just know to look for the hook.
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1155. GatorWX
now its a tornado warning, and nice hook shape too, sorry I underestimated that one.
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Quoting Levi32:


That's ridiculous, it's not rare lol.

Thanks for the link Taz.



your welcome
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1153. Levi32
Quoting GatorWX:


Only a severe thunderstorm warning in place and radar doesn't show a lot of rotation, pretty nasty nonetheless. Not saying it doesn't contain a tornado, but w/o a warning, it's hard to say just by looking at radar.


It's definitely rotating based on radial velocity. There is a strong possibility of either a tornado on the ground or the storm may produce one soon.

Member Since: November 24, 2005 Posts: 635 Comments: 26652
1152. Levi32
Quoting Tazmanian:
Levi32 are you on here ??


i have some more update INFO on EL Nino




-El Nino events rarely develop this early in the summer, and it presently appears that conditions are already nearing the threshold of a basin-wide average anomaly of +0.5 C. Parts of the Eastern Pacific already have anomalies exceeding +1.5 C, and there is a great deal of even warmer subsurface water ready to rise to the surface at any time



more here



Link


That's ridiculous, it's not rare lol.

Thanks for the link Taz.
Member Since: November 24, 2005 Posts: 635 Comments: 26652
1151. GatorWX
Quoting GBguy88:
Dangerous tornado tracking through north-central Nebraska if anyone's interested.


Only a severe thunderstorm warning in place and radar doesn't show a lot of rotation, pretty nasty nonetheless. Not saying it doesn't contain a tornado, but w/o a warning, it's hard to say just by looking at radar.
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1150. GBlet
hey everyone
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Levi32 are you on here ??


i have some more update INFO on EL Nino




-El Nino events rarely develop this early in the summer, and it presently appears that conditions are already nearing the threshold of a basin-wide average anomaly of +0.5 C. Parts of the Eastern Pacific already have anomalies exceeding +1.5 C, and there is a great deal of even warmer subsurface water ready to rise to the surface at any time



more here



Link
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Quoting Levi32:


I missed that comment lol. It's a very nasty tornado.






then oh my lol
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1145. KEEPEROFTHEGATE (Mod)


Member Since: July 15, 2006 Posts: 173 Comments: 54305
1144. Levi32
Quoting Tazmanian:



no there not lol


I missed that comment lol. It's a very nasty tornado.



Member Since: November 24, 2005 Posts: 635 Comments: 26652
Quoting GBguy88:
Dangerous tornado tracking through north-central Nebraska if anyone's interested.



no there not lol
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1141. Levi32
Quoting hurricane2009:
bah i got the numbers wrong lmao

ok let me look this up :p


You got it right. I was thinking of something else.
Member Since: November 24, 2005 Posts: 635 Comments: 26652


AOI @180 hours brushing up against South America.
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'nite all you nature lovers!
Sleep well, be grateful, tomorrow's another day.
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1136. Levi32
Quoting Levi32:


18 hours I think it was.
Quoting hurricane2009:


51


Lol nvm I'm thinking of Humberto records.
Member Since: November 24, 2005 Posts: 635 Comments: 26652
1135. Levi32
Quoting hurricane2009:


Record setting storm too, here is the guess

Guess how many hours it took for Felix to go from being a classified tropical depression to a Category 5 hurricane?


18 hours I think it was.
Member Since: November 24, 2005 Posts: 635 Comments: 26652
Quoting hurricane2009:


Record setting storm too, here is the guess

Guess how many hours it took for Felix to go from being a classified tropical depression to a Category 5 hurricane?

66 hours max 75
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1132. Levi32
Quoting Chicklit:
Felix was a beautiful storm.


Yeah he was:

Member Since: November 24, 2005 Posts: 635 Comments: 26652
1130. GBguy88
Dangerous tornado tracking through north-central Nebraska if anyone's interested.
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Quoting GBguy88:



A haiku follows a 5-7-5 syllable pattern, but you get credit for creativity :P


Translate it back into Japanese and see how many syllables you get.

:p
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Felix was a beautiful storm.
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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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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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