U.S. vulnerability to sea level rise

By: Dr. Jeff Masters , 4:04 PM GMT on June 23, 2009

Share this Blog
2
+

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

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 477 - 427

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28Blog Index

I spun this in the 80's. Never like it much.

UTFO-ROXANNE,ROXANNE-LIVE!!
Quoting Levi32:


Hurricane Roxanne from 1995 is correct.
Member Since: Posts: Comments:
geofory:katrina!!!
Member Since: Posts: Comments:
460- Katrina

461- Dennis
Member Since: Posts: Comments:
Sorry Levi..we both posted at the same time.
Member Since: Posts: Comments:
Quoting jeffs713:

Either Dolly from '96, or Roxanne from '95


Wilma?
Member Since: Posts: Comments:
Quoting hurricane2009:
Name this retired storm that caused $2 billion dollars in damage (2009 dollars) but is largely forgotten due to other more publicized storms hitting the same general area.



Take a guess at this storm


I'm no good at this.. but IVAN??
Member Since: Posts: Comments:
Quoting Levi32:
Ok I learned my lesson next question:

Name this retired major hurricane that hit Cozumel, Mexico causing 1 billion dollars in damage destroying 40000 homes and dumping up to 27 inches of rain in parts of Mexico.


Emily
Member Since: Posts: Comments:
Quoting presslord:
Can we all agree that we couldn't care less about John and Kate?


who????????????
Member Since: Posts: Comments:
Quoting GeoffreyWPB:
Easy one....

img src="Photobucket" alt="" />


Katrina but like H2009 said let's keep this down to 1 person at a time please. Let's answer H2009's challenge first.
Member Since: Posts: Comments:
Quoting Levi32:


Hurricane Roxanne from 1995 is correct.


WOOO! I guessed well!
Member Since: August 3, 2008 Posts: 16 Comments: 5891
Quoting jeffs713:

Either Dolly from '96, or Roxanne from '95
Quoting GeoffreyWPB:
Roxanne or Emily


Hurricane Roxanne from 1995 is correct.
Member Since: Posts: Comments:
i no whats make this more fun oh evere gets the name right will get 2 points per storm and Levi32 can keep track
Member Since: Posts: Comments:
Easy one....

img src="Photobucket" alt="" />
Member Since: Posts: Comments:
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
Roxanne or Emily
Member Since: Posts: Comments:
Quoting Levi32:
Ok I learned my lesson next question:

Name this retired major hurricane that hit Cozumel, Mexico causing 1 billion dollars in damage destroying 40000 homes and dumping up to 27 inches of rain in parts of Mexico.


Either Dolly from '96, or Roxanne from '95
Member Since: August 3, 2008 Posts: 16 Comments: 5891
Quoting Levi32:


Gert 1999 LOL


Gonna have to do some cyberDNA on that one :)

Sorry, did training on data loss protection today. Big brother is really out there folks!

Good slider as the thunder bangs on the door here. Stillwaiting, do you see it north of you ?
Member Since: Posts: Comments:
Quoting hurricane2009:
Ok Levi lol, lets see I will say Keith


Nope :P
Member Since: Posts: Comments:
i love you too
Member Since: Posts: Comments:
Quoting hurricane2009:
no its not dennis or Ivan

um ok we cant do two at once here lol, so go ahead and guess on Levis' first, then we will come back to win


H2009 I haven't heard you guessing you're supposed to love this lol.
Member Since: Posts: Comments:
Quoting Tazmanian:




name this storm


Gert 1999 LOL
Member Since: Posts: Comments:
Roxanne?
Member Since: Posts: Comments:




name this storm
Member Since: Posts: Comments:
Look's like Mitch. . . . .
Member Since: Posts: Comments:
Quoting hurricane2009:


Take a guess at this storm

Katrina
Member Since: Posts: Comments:
Ok I learned my lesson next question:

Name this retired major hurricane that hit Cozumel, Mexico causing 1 billion dollars in damage destroying 40000 homes and dumping up to 27 inches of rain in parts of Mexico.

Member Since: Posts: Comments:
I'm going to go back to bed... its too bloody cold... be back later tonight.
Cheers AussieStorm
Member Since: Posts: Comments:
It was an really great picture of the storm! Thanks!
Member Since: Posts: Comments:
Member Since: Posts: Comments:
Quoting AussieStorm:

Dean


For Belize --

Try these////

Link

Link
Member Since: Posts: Comments:
Quoting Levi32:


Lol how the heck are you supposed to find an image url without the name in it anyway......probably would've been better had you not informed everyone about that lol. [edit] I'll upload the image to a hosting site next time.

Anyway Geoffrey got it right first and stormchaser2007 also got it....Hurricane Iris in 2001

I just send them to my own site, and set up the name as "LOLfooledyou.jpg"
Member Since: August 3, 2008 Posts: 16 Comments: 5891
Quoting Tazmanian:




its Hurricane_Iris


i may want to put that in a link or it may give it a way when you Quote



see LOOL
Member Since: Posts: Comments:
Quoting Levi32:


Lol how the heck are you supposed to find an image url without the name in it anyway......probably would've been better had you not informed everyone about that lol.

Anyway Geoffrey got it right first and stormchaser2007 also got it....Hurricane Iris in 2001




LOL i said it 1st
Member Since: Posts: Comments:
yup its hurricane-dean



5 points or me yay me
Member Since: Posts: Comments:
lol....right click and properties is very helpful!
Member Since: Posts: Comments:
Quoting extreme236:


Just to let you know, if people quote it they can see what it is lol


Lol how the heck are you supposed to find an image url without the name in it anyway......probably would've been better had you not informed everyone about that lol. [edit] I'll upload the image to a hosting site next time.

Anyway Geoffrey got it right first and stormchaser2007 also got it....Hurricane Iris in 2001
Member Since: Posts: Comments:

Viewing: 477 - 427

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28Blog Index

Top of Page

About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

JeffMasters's Recent Photos

Lake Effort Snow Shower Over Windsor, Ontario
Sunset on Dunham Lake
Pictured Rocks Sunset
Sunset on Lake Huron