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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Oh man...you bloggers are great! What if I had said Laverne and Shirley?
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High Geek-ness and Humidity rules here tonight.
Member Since: July 3, 2005 Posts: 428 Comments: 129844
See John tried to take a swipe at me when I was only 3! How cruel :( Good thing he didn't quite make it up here =)

Member Since: November 24, 2005 Posts: 635 Comments: 26700
Very nicely done fellow weather geeks...
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Quoting gator23:


Accordion Shutters on my house.Interesting tid-bit, people who dont have shutters many times think "buy plywood and nails." Nails suck and the wind can blow plywood off secured with nails. If you must use plywood buy heavy duty screws. Heres a handy reminder "SCREW YOU (storm name here)"



Right on target! You can get an inspection around $100, depending on where you are in FL, and get a discount. Most folks don't realize that their insurer is going with the worst case senario for coverage. Meaning you have te worst possible construction on your house. You must prove, via inspection, what you have and they have to give you a discount, per Law in FL.

PS, it is more than just screws, it is the frequency per the NOA. How many per so much distance and any helpers required, washers etc.
Member Since: June 12, 2005 Posts: 6 Comments: 8188
Quoting GeoffreyWPB:
John and Kate...were they famous hurricanes?


I'm bad at history but Kate was the latest-forming major hurricane and one of the latest hurricanes to strike the US (Florida).

John has the record for coming the closest to hitting me lol. He also crossed into both Pacific basins being a hurricane during the first half of his life and a typhoon the next. He is also the longest-living farthest-traveling tropical cyclone ever observed.
Member Since: November 24, 2005 Posts: 635 Comments: 26700
Quoting GeoffreyWPB:
Ernesto was nothing here in West Palm / Lake Worth...Sunny for most of the day.


Becuase it effected Palm Beach minimally.
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John and Kate...were they famous hurricanes?
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At least people have discarded the idea of putting tape on their windows.
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Can we all agree that we couldn't care less about John and Kate?
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Quoting hurricane2009:


July 10th

Climatology
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Ernesto was nothing here in West Palm / Lake Worth...Sunny for most of the day.
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359. HadesGodWyvern (Mod)
Japan Meteorological Agency
Tropical Cyclone Advisory #11
TROPICAL STORM NANGKA (T0904)
9:00 AM JST June 24 2009
===================================

Subject: Category One Typhoon Overland The Philippines

At 0:00 AM UTC, Tropical Storm Nangka (994 hPa) located at 12.6N 122.4E has 10 minute sustained winds of 40 knots with gusts of 60 knots. The storm is reported as moving west at 8 knots.

Gale-Force Winds
================
180 NM from the center

Dvorak Intensity: T2.5

Forecast and Intensity
=====================
24 HRS: 14.9N 119.6E - 40 knots (Tropical Storm/CAT 1)
48 HRS: 18.2N 118.7E - 45 knots (Tropical Storm/CAT 1)
72 HRS: 21.5N 118.2E - 40 knots (Tropical Storm/CAT 1)
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Quoting stillwaiting:
good evening everyone!!!,I see we have the first hurricane of 09'!!!!,I had a feeling 2 days ago this would be our first hurricane,alot on here had doubt.......

I See the west coast of FL w/be having a fun night w/some strong and isolated severe strorms moving south as energy near the big bend moves down the coast!!

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.
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Quoting Ossqss:
If anyone is looking to improve their survival rate from a hurricane, you should be looking at this stuff. I use it myself, 8'ers on the back porch. The clear panels are awesome for you can typically leave them up all season and not worry about them. The H (top) header in the picture means you only have to secure the bottom. If you do this per the directions (NOA's), you don't just get a feeling of protection, you get discount on your insurance ,mandatory, and the added benefit of improved house value, at least in Florida. Just tryin to help if I can :)



Accordion Shutters on my house.Interesting tid-bit, people who dont have shutters many times think "buy plywood and nails." Nails suck and the wind can blow plywood off secured with nails. If you must use plywood buy heavy duty screws. Heres a handy reminder "SCREW YOU (storm name here)"
Member Since: Posts: Comments:
good evening everyone!!!,I see we have the first hurricane of 09'!!!!,I had a feeling 2 days ago this would be our first hurricane,alot on here had doubt.......

I See the west coast of FL w/be having a fun night w/some strong and isolated severe strorms moving south as energy near the big bend moves down the coast!!
Member Since: October 5, 2007 Posts: 20 Comments: 4970
Quoting potteryX:
Good to see that, Aussie.
It is the first post, in months here, talking about cool temps. LOL

I have been posting here everyday
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If anyone is looking to improve their survival rate from a hurricane, you should be looking at this stuff. I use it myself, 8'ers on the back porch. The clear panels are awesome for you can typically leave them up all season and not worry about them. The H (top) header in the picture means you only have to secure the bottom. If you do this per the directions (NOA's), you don't just get a feeling of protection, you get discount on your insurance ,mandatory, and the added benefit of improved house value, at least in Florida. Just tryin to help if I can :)

Member Since: June 12, 2005 Posts: 6 Comments: 8188
Homebush, Sydney, Australia at 11:30 EST
Temperature:11.4°C (52.5°F)
Dew point:9.1°C (48.4°F)
Relative humidity:86%
Feels like:10.7°C (51.3°F)
Wind:W 7km/h (4.3mph)
Wind gusts:13km/h (8mph)
Rainfall since 9am/last hr:0.2mm / 0.0mm
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Quoting hurricane2009:


dont shot the messenger someone else brought up the "lack" of tropical activity lately in south florida lol

I was thinking of those storms too really


I think he was saying lack of afternoon thunderstorms. He is wrong it has been raining every afternoon here since the dawn of time.
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Member Since: July 3, 2005 Posts: 428 Comments: 129844
Quoting G35Wayne:
2 2 2

3 3 3?
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2 2 2
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Afternoon showers are the norm in summer here in Florida. They become severe I did not notice any difference from today than usual
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Good to see that, Aussie.
It is the first post, in months here, talking about cool temps. LOL
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The economy is in real bad shape, but does WU have to accept advertisements for this total scam?

I see this banner on WU and we are all smart enough to know there ain't no way!

http://www.power4home.com/index2.php?hop=ttinc1

Sorry for the rant, but people are getting screwed with this scam and a couple of others that claim the same. If I get banned, so be it.
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Quoting hurricane2009:
Florida gets severe weather all the time in the summer months, this is common from May - August this happens, this is actually the return to the normal pattern that we had in the 90s of afternoon storms, after about 1998 we saw less and less of these severe storms. So really these storms are normal if you really think about it and the last 10 years of not having them was the irregular part.

The lack of these severe events has nothing to do with the "lack" of tropical systems. South Florida has been fairly lucky compared to other parts of the coastline in the last few years, so your "lack" of tropical systems is pretty much contained to only your area, many of us have seen way too much activity.


Wilma, Rita, Enrnesto, Katrina, Fay, Charley... how was south florida lucky?
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Sydney is heading for its coldest day of the year. Its 11:30am and only 11C.
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We had a solid wood door on the front of our office during Andrew. The abestos roof tiles came like little hatchets and stuck in the door.

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Saying goodnight to Andres...

Notice how there's kind of a line from SW to NE where the convection rapidly gets cut off. That's pretty much where the dry stable airmass over cold SSTs begins. Andres may be able to rebuild the SE portion of the CDO but I don't expect any significant strengthening phase out of him tonight.

Member Since: November 24, 2005 Posts: 635 Comments: 26700
Quoting hurricane2009:


touche you know people are bored when you start analyzing the weather in Florida, fact is there is no rhyme or reason to the weather in Florida lol

Its why I love living here, keeps you on your toes lol

my reason is at least you have a summer here unlike NE sorry NEWXguy SNE was always too cool for me in summer.
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Had to share this also...

Which way do you think it entered the tree?

That's impressive in relation to weather and how we put up what we think will help us. That is someones plywood covering on an opening in their house during Andrew. Wow....

Better fastening methods would have prevented this from happeing.

Member Since: June 12, 2005 Posts: 6 Comments: 8188
Quoting AussieStorm:
Can someone explain how this is still a Hurricane???


The only explananation I can think of is that Andres was much stronger yesterday than we ever thought. I'm thinking it could have been as strong as an 80-knot Cat 1, and then when it got stripped of convection it weakened to the intensity that the recon found it at. It was spared from rapid weakening by its impressive low-level structure, and now it's trying to rebuild the CDO.
Member Since: November 24, 2005 Posts: 635 Comments: 26700
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Quoting HIEXPRESS:
In Florida, having weather that isn't anomalous would be an anomaly.
In other words, always pack a rain jacket, carry an umbrella, expect the un-expected, and the rain chance always increases by 40% when my brother-in-law goes fishing with you, always!!!
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Can someone explain how this is still classified as a Hurricane???
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---
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Quoting KoritheMan:


Some say that the 1997 El Nino was stronger than the 1982-1983 event, which unfortunately, I don't have anomalies for.

That being said, the 1982-1983 event was quite strong, evidenced by the fact that the Atlantic was terribly inactive in both years (6 storms the first year, 4 the next). For the 1997 El Nino to surpass that is quite remarkable indeed.


Based on SST anomalies 1997 was clearly stronger and for a longer time.
Member Since: November 24, 2005 Posts: 635 Comments: 26700
In Florida, having weather that isn't anomalous would be an anomaly. ;)
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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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