Two 500-year floods in 15 years

By: Dr. Jeff Masters , 2:48 PM GMT on June 19, 2008

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The U.S. Geological Survey has preliminary data showing that this month's floods on four of Iowa's rivers--the Cedar, Iowa, Shell Rock, and Wapsipinicon--were 500-year floods. Back in 1993, many rivers in the Midwest also experienced 500-year floods, so the region has endured two 500-year floods in the past 15 years. How can this be? First of all a definition--a 500-year flood is an event that has only a 0.2% chance of occurring in a given year, based on available river flow data. Of course, reliable data only goes back a century at most, so designation of a 500-year flood event is somewhat subjective. Still, it seems rather improbable that two such huge floods should occur within such a short time span, raising the question of whether the floods were, in part, human-caused.

In a provocative story in the Washington Post today, it was pointed out that part of the flooding is due to the draining of wetlands for farming purposes. As nature's natural buffers against flooding are drained and filled to provide room for more farmland, run-off and flooding are bound to increase. Furthermore, as more levees are built to protect more valuable farmland and new developments, flood waters are pushed out of the former areas they were allowed to spread out in and forced into river channels behind the new levees. Even higher levees must then be constructed to hold back the increased volume of water they are asked to contain.

Climate change contributing to flooding?
The heaviest types of rains--those likely to cause flooding--have increased in recent years (see my February blog, "The future of flooding", for more detail). According to the United Nations' Intergovernmental Panel on Climate Change (IPCC) 2007 report, "The frequency of heavy precipitation events has increased over most land areas". Indeed, global warming theory has long predicted an increase in heavy precipitation events. As the climate warms, evaporation of moisture from the oceans increases, resulting in more water vapor in the air. According to the 2007 IPCC report, water vapor in the global atmosphere has increased by about 5% over the 20th century, and 4% since 1970.

Over the U.S., where we have very good precipitation records, annual average precipitation has increased 7% over the past century (Groisman et al., 2004). The same study also found a 14% increase in heavy (top 5%) and 20% increase in very heavy (top 1%) precipitation events over the U.S. in the past century. Kunkel et al. (2003) also found an increase in heavy precipitation events over the U.S. in recent decades, but noted that heavy precipitation events were nearly as frequent at the end of the 19th century and beginning of the 20th century, though the data is not as reliable back then. Thus, climate change is likely partly to blame for increased flooding in the U.S., although we cannot rule out long-term natural variations in precipitation.


Figure 1. Forecast change in precipitation and runoff for the period 2080 to 2099 compared to 1980 to 1999. The forecasts come from the A1B scenario from multiple climate models used for the Intergovernmental Panel on Climate Change (IPCC) 2007 report.

The forecast
According to a multi-model consensus of the climate models run for the Intergovernmental Panel on Climate Change (IPCC) 2007 report, precipitation and river runoff for the Mississippi River drainage basin are expected to increase only slightly by the end of this century (Figure 1). However, more of this rain is expected to fall in heavy precipitation events, the ones most likely to cause flooding. As a result, the U.S. needs to prepare for an increase in the number and severity of 100-year and 500-year flooding events in the coming century.

References
Kunkel, K. E., D. R. Easterling, K. Redmond, and K. Hubbard, 2003, "Temporal variations of extreme precipitation events in the United States: 1895.2000", Geophys. Res. Lett., 30(17), 1900, doi:10.1029/2003GL018052.

Groisman, P.Y., R.W. Knight, T.R. Karl, D.R. Easterling, B. Sun, and J.H. Lawrimore, 2004, "Contemporary Changes of the Hydrological Cycle over the Contiguous United States: Trends Derived from In Situ Observations," J. Hydrometeor., 5, 64.85.

Tropics
It's quiet in the tropics. There are no threat areas to discuss, and none of the models are forecasting tropical storm formation in the next seven days.

Jeff Masters

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603. WeatherfanPR
5:12 PM GMT on June 20, 2008
some very welcome rain here in Carolina PR.

About the wave near Puerto Rico I see a little bit of a broad circulation but not a close one.

That wave near de CV islands looks very impressive. This Hurricane Season could be very active indeed with lots of strong tropical waves.

thanks for the link cchsweatherman
Member Since: August 23, 2006 Posts: 0 Comments: 1583
601. all4hurricanes
5:21 PM GMT on June 20, 2008
599
Jesse?
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600. all4hurricanes
5:20 PM GMT on June 20, 2008
Remember this
OK place your bets what places will get hit by a devastating hurricane this year

1. The Carolinas
2. Texas
3. New England
4. Puerto Rico
5. North East Coast of Florida
6. Hispaniola
7. Cuba
8. Mexico
9. Leeward Islands
10. Central america
11. Jamaica
12. Gulf Coast

Well by the looks of how this season is starting the answer is 1-12 especially 4 and 9


Notice how Middle Gulf states arn't on this Like you don't really think about the monster hurricane that hit ... Virginia?
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599. Drakoen
5:20 PM GMT on June 20, 2008
597. jphurricane2006 5:20 PM GMT on June 20, 2008
and my name, which does start with "J" is one of the most common names in the world and yet accept for an adaptation of it (which is what my dad goes by) is used in Australia


John, Johnny, Joe, James?
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598. Weather456
1:19 PM AST on June 20, 2008
Jp, lol

Drak yea...I remembered :)
Member Since: July 24, 2005 Posts: 407 Comments: 19076
596. Drakoen
5:18 PM GMT on June 20, 2008
...TROPICAL WAVES...

AN ATLANTIC TROPICAL WAVE IS ALONG 25W/26W S OF 14N MOVING W
NEAR 20 KT. VISIBLE SATELLITE IMAGERY CLEARLY INDICATES CYCLONIC
TURNING NEAR 8N-9N. THE MIMIC-TPW ANIMATION DEPICTS A MOISTURE
SURGE BETWEEN 21W-26W. LOW-LEVEL SATELLITE DERIVED WINDS AS WELL
AS ASCAT DATA SUPPORT THE AXIS POSITION. CLUSTERS OF SCATTERED
MODERATE/ ISOLATED STRONG CONVECTION ARE FROM 7N-9N BETWEEN
25W-27W AND FROM 10N-11N BETWEEN 23W-27W.

A TROPICAL WAVE IS IN THE EASTERN CARIBBEAN ALONG 64W S OF 19N
MOVING W AT 15-20 KT. VISIBLE SATELLITE IMAGERY DISPLAYS A BROAD
AREA OF CYCLONIC TURNING ASSOCIATED WITH THE WAVE. SFC PRESSURES
IN THE LESSER ANTILLES ARE BEGINNING TO RISE BEHIND THE WAVE AS
IT CONTINUES TO MOVE WESTWARD. NUMEROUS SHOWERS AND
THUNDERSTORMS ARE BEHIND THE WAVE AXIS FROM 12N-18N W OF 59W.
GUADALOUPE ISLAND REPORTED A 24 HR PRECIP TOTAL OF 1.65 INCHES.
MIMIC-TPW ANIMATION INDICATES A MOISTURE BULGE ALONG THE WAVE
AXIS. THE WAVE IS EXPECTED TO REACH THE DOMINICAN REPUBLIC EARLY
SATURDAY.
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595. Weather456
1:18 PM AST on June 20, 2008
586...lol

590...From Puerto Rico or the Virgin Isles (British or US)?
Member Since: July 24, 2005 Posts: 407 Comments: 19076
594. JLPR
5:13 PM GMT on June 20, 2008
Remember this
OK place your bets what places will get hit by a devastating hurricane this year

1. The Carolinas
2. Texas
3. New England
4. Puerto Rico
5. North East Coast of Florida
6. Hispaniola
7. Cuba
8. Mexico
9. Leeward Islands
10. Central america
11. Jamaica
12. Gulf Coast

Well by the looks of how this season is starting the answer is 1-12 especially 4 and 9


Well that doesn't make me feel happy =P
Member Since: September 4, 2007 Posts: 36 Comments: 5223
593. all4hurricanes
5:17 PM GMT on June 20, 2008
My actual first name is Kurt so German isn't it
I'm disappointed that it will never be a hurricane name
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591. Drakoen
5:17 PM GMT on June 20, 2008
588. Weather456 5:16 PM GMT on June 20, 2008
584. Drakoen 1:13 PM AST on June 20, 2008

Very funny Boots

My first name is Derrick.


It was an inside joke from last year. I guess you don't remember....
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590. all4hurricanes
5:15 PM GMT on June 20, 2008
yep it's George 1998
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589. pottery
1:15 PM AST on June 20, 2008
Hello, heavy rain and rumbling sky here in Trinidad.
Vary nice man.
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588. Weather456
1:15 PM AST on June 20, 2008
584. Drakoen 1:13 PM AST on June 20, 2008

Very funny Boots

My first name is Derrick.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
587. Drakoen
5:14 PM GMT on June 20, 2008
When was the last time Puerto Rico was hit by a devastating hurricane lol??? long-live hurricane George.
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586. all4hurricanes
5:14 PM GMT on June 20, 2008
I'm Hanna Montana lol
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584. Drakoen
5:12 PM GMT on June 20, 2008
581. jphurricane2006 5:11 PM GMT on June 20, 2008
you know it would be interesting to know the first names of some people here lol

well lets see we know IKE, Mel is Melissa duh, and apparently Ipswich is Fred lol


Weather456 is spongebob
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583. groundswell
5:06 PM GMT on June 20, 2008
Shear is clearly keeping t-wave in check. But it is trackable and offers potential should conditions ease. Doesn't look like any surf from this one.
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582. all4hurricanes
5:04 PM GMT on June 20, 2008
Remember this
OK place your bets what places will get hit by a devastating hurricane this year

1. The Carolinas
2. Texas
3. New England
4. Puerto Rico
5. North East Coast of Florida
6. Hispaniola
7. Cuba
8. Mexico
9. Leeward Islands
10. Central america
11. Jamaica
12. Gulf Coast

Well by the looks of how this season is starting the answer is 1-12 especially 4 and 9
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579. Weather456
1:09 PM AST on June 20, 2008
573. cchsweatherman 12:57 PM AST on June 20, 2008

seen
Member Since: July 24, 2005 Posts: 407 Comments: 19076
578. Drakoen
5:08 PM GMT on June 20, 2008
572. IpswichWeatherCenter 4:57 PM GMT on June 20, 2008

If that ain't not organised enough to get a mention in the TWO or be a T.D my name is Fred


Hi Fred!
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577. Weather456
12:59 PM AST on June 20, 2008
572. IpswichWeatherCenter 12:57 PM AST on June 20, 2008

That image is around 7 this morning. A more recent image show convection has wane some. Persistence is key.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
576. Weather456
12:58 PM AST on June 20, 2008
571. StormW 12:57 PM AST on June 20, 2008
563.

Appears to be a very broad circulation west of your circle, near 16N;66W. Wind shear is blowing the cloud tops east.


There is where I see it too.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
574. melwerle
4:57 PM GMT on June 20, 2008
Morning Storm!
Member Since: June 28, 2006 Posts: 12 Comments: 1837
573. cchsweatherman
12:55 PM EDT on June 20, 2008
567. Weather456 12:54 PM EDT on June 20, 2008
563. cchsweatherman 12:49 PM AST on June 20, 2008

I see some slight hints of turning, but what ever is there is very ill-define or atleast not at the surface, I could barely find a westward moving cloud element south of the suspected area.


In my opinion, a surface circulation may just be starting development in that area and could be why we may not be seeing any westward movement in the clouds. Now that it has emerged into lower wind shear, this tropical wave may be trying to get together now. Still think development with the tropical wave seems unlikely at this time, but I'm not going to discount it.
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572. IpswichWeatherCenter
4:56 PM GMT on June 20, 2008


If that ain't not organised enough to get a mention in the TWO or be a T.D my name is Fred
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570. Weather456
12:55 PM AST on June 20, 2008
But it seems to some consolidation of convection near that area. Just have to watch and see. Persistence is key.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
569. Weather456
12:54 PM AST on June 20, 2008
563. cchsweatherman 12:49 PM AST on June 20, 2008

I see some slight hints of turning, but what ever is there is very ill-define or atleast not at the surface, I could barely find a westward moving cloud south of the suspected area.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
568. RasBongo
4:53 PM GMT on June 20, 2008
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567. Weather456
12:50 PM AST on June 20, 2008
....Double post
Member Since: July 24, 2005 Posts: 407 Comments: 19076
566. RasBongo
4:42 PM GMT on June 20, 2008
http://cimss.ssec.wisc.edu/tropic/real-time/wavetrak/winds/m8g10split.jpg
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565. AWeatherLover
12:51 PM EDT on June 20, 2008
563. CCHS- I see some circulation there too.
Can anyone post a shear map for this area? Thanks!
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564. AWeatherLover
12:51 PM EDT on June 20, 2008
Afternoon Storm!
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563. cchsweatherman
12:40 PM EDT on June 20, 2008
Photobucket

Go to the RAMSDIS site and loop the visible imagery for the tropical wave. Zoom into the area I have encircled above. Just my observation here, but I see a surface circulation in that area in association with this tropical wave. Earlier today, I had seen an observation come from Dominica and Martinique depicting a NW wind when this had passed through the area. Thoughts?
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561. Weather456
12:29 PM AST on June 20, 2008
CCH, there are conlficting observations. Surface obs clearly show cyclonic turning near the yellow circle, while visible loops show turning near the red circle. I think the surface obs should be discarded if they are inconsistent over the next hour, and the one seen on visible imagery is rather ill-define.


Member Since: July 24, 2005 Posts: 407 Comments: 19076
560. RasBongo
4:39 PM GMT on June 20, 2008
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559. Drakoen
4:40 PM GMT on June 20, 2008
Doesn't look like we will have any June storms forming this year.
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558. RasBongo
4:38 PM GMT on June 20, 2008
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557. RasBongo
4:29 PM GMT on June 20, 2008
Dry air in the CATL is dissipating fast, and is not going to come back anytime soon.



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556. cchsweatherman
12:31 PM EDT on June 20, 2008
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554. grayingwindsurfer
3:15 PM GMT on June 20, 2008
One other comment on flooding & climate change:
Milly and others have shown annual runoff in large river basins in northern latitudes has been increasing and that climate models (in hindcast mode) do a good job of matching these increases. More importantly, if increasing greenhouse gas concentrations are left out of the models (again, in hindcast mode) the models do a poor job of matching the increased runoff. Although this alone is not definitive, it is yet another VERY STRONG argument that human-induced increases in greenhouse gases are changing the climate and causing increased likelihood of flooding, especially in northern latitudes.
Obviously any individual event can NOT be directly attributed to climate change, but the increased chances of it occurring (or re-occurring) CAN be, at least in part.
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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.