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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454. RasBongo
2:36 PM GMT on June 20, 2008
451

The amazing part is that it starts to rotate so far in the EATL
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453. all4hurricanes
2:37 PM GMT on June 20, 2008

I know storms can strengthen over the Philippines and that it happened just in 2006 but they actually forecast it that seems a little... odd
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452. IKE
9:34 AM CDT on June 20, 2008
447...it worked. I see the turning.
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450. TampaSpin
10:33 AM EDT on June 20, 2008
445. Skyepony 10:32 AM EDT on June 20, 2008

Lets hope so, i'm not resoding my lawn 2 years in a row......lol.....
Member Since: September 2, 2007 Posts: 179 Comments: 20448
449. Weather456
2:27 PM GMT on June 20, 2008
the wave in the EATL has nice mid-level turning
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447. RasBongo
2:28 PM GMT on June 20, 2008
414
428

Let's hope this time it works:
Link
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446. IKE
9:31 AM CDT on June 20, 2008
The Yucatan...it looks like some moisture that gets drawn NNE with a front/trough coming down.
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445. Skyepony (Mod)
2:27 PM GMT on June 20, 2008
Tampaspin~ I hope the forecasted SW flow can pull some of that tropical moisture too us.

456~ Happy rainy day.

Member Since: August 10, 2005 Posts: 223 Comments: 39356
444. melwerle
2:31 PM GMT on June 20, 2008
Morning Everyone -

Looks like things are rather quiet - anything I'm missing?

Have a great day...

Melissa
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443. OUSHAWN
2:29 PM GMT on June 20, 2008
Tampa...looks like you beat me to it...LOL
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442. TampaSpin
10:28 AM EDT on June 20, 2008
440. OUSHAWN 10:28 AM EDT on June 20, 2008

LOL beat ya by 1 minute....lol
Member Since: September 2, 2007 Posts: 179 Comments: 20448
440. OUSHAWN
2:24 PM GMT on June 20, 2008
I'm actually keeping an eye on the GOM...mainly right north of the Yucatan. There looks to be a hint of a circulation there and now there seems to be storms firing up right around where the center of that circulation would be. I could be wrong about the circulation but it just looks to be.
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439. TampaSpin
10:22 AM EDT on June 20, 2008
Ike i am starting the think the tip of the Yucatan could get rather interesting.....alot of convection gathering.
Member Since: September 2, 2007 Posts: 179 Comments: 20448
438. IKE
9:24 AM CDT on June 20, 2008
436...

I see that...shear is low.
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437. Weather456
2:24 PM GMT on June 20, 2008
Been raining here since about 8....first wet wave of the rainy season, atleast for here.
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436. Skyepony (Mod)
2:21 PM GMT on June 20, 2008
How bout that blow up in the EPac..

See under the Atlantic floaters one is marked Fengshen & shows South Central America. Someone needs more coffee.
Member Since: August 10, 2005 Posts: 223 Comments: 39356
435. Weather456
2:21 PM GMT on June 20, 2008
432...The Mother Colony of the ECARIB...Saint Kitts
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434. Skyepony (Mod)
2:19 PM GMT on June 20, 2008
Fengshen
Member Since: August 10, 2005 Posts: 223 Comments: 39356
433. IKE
9:19 AM CDT on June 20, 2008
Slight blowup on that rainbow loop near 15N and 63W.
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432. 69Viking
9:14 AM CDT on June 20, 2008
424. Weather456

My Island = ?
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431. Skyepony (Mod)
2:17 PM GMT on June 20, 2008
Rainbow loop
Member Since: August 10, 2005 Posts: 223 Comments: 39356
430. IKE
9:15 AM CDT on June 20, 2008
The Caribbean queen wave looks like it's heading for Jamaica.....

Dreadlock Holiday?

It's near 15N and 63W.
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429. franck
2:15 PM GMT on June 20, 2008
427...quite quiet.
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428. 69Viking
9:05 AM CDT on June 20, 2008
411. RasBongo

I won't work with http entered twice. Edit to take out the second http.
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427. catastropheadjuster
1:45 PM GMT on June 20, 2008
Good Morning everyone. Is anything going on in the tropics? Or is it quite.
Sheri
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425. IKE
9:11 AM CDT on June 20, 2008
422. HurakanPR 9:10 AM CDT on June 20, 2008
Great song Ike, bringing back memories,,,!!!!


Long version...album quality sound. I read in Rolling Stone that albums have made a slight comeback.
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424. Weather456
2:07 PM GMT on June 20, 2008
419. jphurricane2006 2:07 PM GMT on June 20, 2008

My island, hasnt suffered any hurricane conditions in 10 years. We had to close our ports during Lenny and Dean. We had significant beach erosion and TS conditions during Lenny, Fabian, Frances, Ivan, Jeanne, Chris and Dean.
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423. IKE
9:10 AM CDT on June 20, 2008
421. jphurricane2006 9:09 AM CDT on June 20, 2008
yeah it does, I wish I could see a loop of it lol


Same here...can someone link a loop of the east Atlantic.
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422. HurakanPR
9:59 AM AST on June 20, 2008
Great song Ike, bringing back memories,,,!!!!
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420. IKE
9:06 AM CDT on June 20, 2008
That Eastern Atlantic wave looks impressive.
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418. IKE
9:05 AM CDT on June 20, 2008
415....oops...I didn't read the discussion from Tampa this morning...I read Key West. They didn't mention anything about a system.
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417. IKE
9:04 AM CDT on June 20, 2008
413....yeah this year you may have to pay-up somewhere in the island chain........
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416. pearlandaggie
2:02 PM GMT on June 20, 2008
410. totally agreed, viking. at some point i think we have to understand that the benefits of land use/modification do have some downsides, particularly things like this.
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415. Buhdog
1:59 PM GMT on June 20, 2008
Ike....

Got that from our NWS forecast details....

Link
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414. IKE
9:03 AM CDT on June 20, 2008
411.

It doesn't work again...
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413. Weather456
2:01 PM GMT on June 20, 2008
Waves continue to be impressive, August is goin to be hellish....hope I'm wrong...10 years without a hurricane is rather long and lucky for a caribbean island. :D

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412. IKE
9:00 AM CDT on June 20, 2008
Shear is dropping around and to the west/NW of the wave...it's soon to get in less than 30 knots of shear....

1200UTC CIMSS Shear Map
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411. RasBongo
1:56 PM GMT on June 20, 2008
Try this one:

Link

Check the most eastern side of the animation. In the last two frames you can see the start of a rotation.
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410. 69Viking
8:55 AM CDT on June 20, 2008
391. pearlandaggie

I think the real point here is they built levees to hold back water from the flood plains the rivers typically used during times of heavy rain. After the levees were built people then built homes on the flood plain. If the levees were never built to restrict a rivers natural flow the flooding would not be this severe. How GW has an effect on the human error of building the levees is beyond me.
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409. IKE
8:57 AM CDT on June 20, 2008
407. Weather456 8:55 AM CDT on June 20, 2008
Ike, oh, I see what u were saying....Mexico isnt apart of Central America. So when I mentioned central America, I was generalizing the area between the USA and Colombia. My bad.


OK.
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408. Tazmanian
6:55 AM PDT on June 20, 2008
from what i can tell from the WU maps this could be the last cold front of the season for the E coast be come i dont see any more cold front on are WU map back W


bye bye cold fronts in tell next season
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407. Weather456
1:53 PM GMT on June 20, 2008
395....Ike, oh, I see what u were saying....Mexico isnt apart of Central America. So when I mentioned central America, I was generalizing the area between the USA and Colombia. My bad.
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406. IKE
8:53 AM CDT on June 20, 2008
400. Buhdog 8:51 AM CDT on June 20, 2008
From my local met in south florida...

MODEL DATA INSISTS IN DEVELOPING A TROPICAL FEATURE APPROACHING THE
NORTHERN CARIBBEAN AND THE FLORIDA KEYS BY MID WEEK WHICH COULD
BRING INCREASING LOW LEVEL MOISTURE ALONG WITH INSTABILITY OVER THE
AREA. HOWEVER...WILL WAIT FOR MORE PERSISTENCE OF THIS FEATURE IN
THE NEXT COUPLE OF DAYS BEFORE FURTHER INCREASING POPS AROUND THE
SOUTHERN HALF OF THE CWA.


What models? I don't see any yet.
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405. TheCaneWhisperer
1:41 PM GMT on June 20, 2008
That 1030mb sprawling high will keep a cap on things for a while. It's also enhancing the dust activity as well which, is supposed to be below normal this year. Models are forecasting this high to strengthen more through next week, ahhhh. peace in the tropics.
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404. IKE
8:52 AM CDT on June 20, 2008
RasBongo....bong hits? LOL...

Your link doesn't work...sorry.
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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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