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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654. Fishizzle
8:15 PM GMT on June 20, 2008
We have a beautiful show moving into Stuart currently from the South West. I hope it brings some good rain with it.
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653. Patrap
3:13 PM CDT on June 20, 2008
Gulf of Mexico (Updated every ~10-15 mins.)
IR,WV and Low Cloud Visible. Link

GOES IR Loop of the GOM Link
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652. Floodman
3:09 PM CDT on June 20, 2008
IS the blog still acting up?
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651. OSUWXGUY
7:39 PM GMT on June 20, 2008
Oh...I just looked at the models and the shear is forecast to pick up a bunch by tomorrow...basically a non-issue
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650. OSUWXGUY
7:31 PM GMT on June 20, 2008
Sonofagunn-

I was interested in the same flare up...


though pressures are fairly high and low level vorticity is pretty much non-existant

I'm going to keep an eye on it just as a precaution...because SSTs are warm and shear in the Gulf is fairly favorable...unlike the rest of the Atlantic.
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649. sonofagunn
7:25 PM GMT on June 20, 2008
Should we start blob watching the middle of the GOM?
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648. IpswichWeatherCenter
7:24 PM GMT on June 20, 2008


Anyone know where the eye is?
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647. kmanislander
7:16 PM GMT on June 20, 2008
It looks as if the wave axis is closing in on this buoy

Link
Member Since: August 19, 2006 Posts: 0 Comments: 15842
645. Tazmanian
7:11 PM GMT on June 20, 2008
what do you see here???

Link
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644. kmanislander
7:09 PM GMT on June 20, 2008
UR welcome PR

Member Since: August 19, 2006 Posts: 0 Comments: 15842
643. HurakanPR
3:03 PM AST on June 20, 2008
Thank you Kmaninslander, great information, it was exactly what i experienced, strong gustly winds, and heavy rain. Then i look at the map of Puerto Rico and my area was cover by the outflow boundary from the wave. Thanks for the input and the well documentated information. Love to learn!
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642. CJ5
7:02 PM GMT on June 20, 2008
Interesting feature at 14/65 on the 18:15 RGB (Caribbean)
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641. Drakoen
7:00 PM GMT on June 20, 2008
636. kmanislander 6:56 PM GMT on June 20, 2008
Drak

The 700 mb vorticity is oriented ENE to WSW whereas the 850 mb map shows a more concentrated circle of vorticity. Either way there will be little in the way of a surface low with all the thunderstorms being decapitated as quickly as they form.

Zoom in and compare 850mb with 700mb. The 850mb vorticity by 16N 66w with the presence of the 700mb vortex father east.
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640. kmanislander
7:00 PM GMT on June 20, 2008
HI PR

Here is a link to a discussion about gust fronts associated with outflow boundaries. The image I posted is one of several I have seen today around the PR area from collapsing thunderstorms associated with the wave.

Link
Member Since: August 19, 2006 Posts: 0 Comments: 15842
638. HurakanPR
2:52 PM AST on June 20, 2008
Well i guess is the outflow boundary mention by Kmaninslander that is hitting my zone.
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636. kmanislander
6:53 PM GMT on June 20, 2008
Drak

The 700 mb vorticity is oriented ENE to WSW whereas the 850 mb map shows a more concentrated circle of vorticity. Either way there will be little in the way of a surface low with all the thunderstorms being decapitated as quickly as they form.
Member Since: August 19, 2006 Posts: 0 Comments: 15842
635. Tazmanian
6:53 PM GMT on June 20, 2008
ZCZC MIATWOEP ALL
TTAA00 KNHC DDHHMM
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1100 AM PDT FRI JUN 20 2008

FOR THE EASTERN NORTH PACIFIC...EAST OF 140 DEGREES WEST LONGITUDE..

1. AN AREA OF DISTURBED WEATHER IS LOCATED ABOUT 750 MILES SOUTH-
SOUTHWEST OF THE SOUTHERN TIP OF BAJA CALIFORNIA. DEVELOPMENT...IF
ANY...OF THIS SYSTEM IS EXPECTED TO BE SLOW TO OCCUR.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE NEXT
48 HOURS.
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634. Drakoen
6:48 PM GMT on June 20, 2008
630. kmanislander 6:48 PM GMT on June 20, 2008
The Caribbean wave is holding on to its rotation at the 5000 foot level ( 850 mb ) but there is nothing I am seeing to suggest anything at the surface.


I think its more towards 700mb which is typical of tropical waves and matches well with the cimss 700mb vorticity.
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633. myway
6:48 PM GMT on June 20, 2008
cane
Good post.
Just had a storm here in Boca with small hail decent winds and rain. It moved thru pretty fast. No need for warning, it is the price we pay tp live in paradise.
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632. kmanislander
6:49 PM GMT on June 20, 2008
Outflow boundary heading NW away from PR

Member Since: August 19, 2006 Posts: 0 Comments: 15842
631. HurakanPR
2:45 PM AST on June 20, 2008
Im in the west coast, near Aguadilla, Puerto Rico,strong thunder storms,very windy, but then again it could be because the convection produce for the afternoon heat.
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630. kmanislander
6:45 PM GMT on June 20, 2008
The Caribbean wave is holding on to its rotation at the 5000 foot level ( 850 mb ) but there is nothing I am seeing to suggest anything at the surface. Shear is doing a number on it and the thunderstorms keep collapsing as fast as they build. This is evident from yet another outflow boundary seen near PR in the current sat images.Conditions ahead of it are still in the 30 knot range.

Link
Member Since: August 19, 2006 Posts: 0 Comments: 15842
629. TheCaneWhisperer
6:42 PM GMT on June 20, 2008
623. yamil20 6:17 PM GMT on June 20, 2008 Hide this comment.
i am piss with the NWS in miami,here in hialeah we have like a storm right know with a lot of winds,and no even a special statement in tv nothing!! we are humans.


Humans that live in South Florida where these run of the mill T-Storms happen everyday for the most part. NWS considered issuing a Severe T-Storm watch Wedensday, not sure if they ended up doing it or not but, those were some nasty storms. 60+mph winds, hail, lightning and thunder you would not believe here in Palm Beach Gardens. The winds blew several cars together, causing accidents. Storms like that deserve a special statement, in my opinion, not run of the mill T-Storms.
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628. WeatherfanPR
6:36 PM GMT on June 20, 2008
no rain or wind, just very sunny conditions here in Carolina PR.
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627. Drakoen
6:37 PM GMT on June 20, 2008
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626. HurakanPR
2:20 PM AST on June 20, 2008
Well on thing is for sure im about a hundred miles away from the apparent COC if there is one of the little wave,in the island of Puerto Rico, and we are getting winds 20 mph, gusting to 35, with clouds moving south east, showing ciclonical movement,any comments?
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624. melwerle
6:17 PM GMT on June 20, 2008
Boat is rigged and I'm waiting for it to blow in - would like to pull a scene from Forrest Gump... "is that all you have?!!!"
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623. yamil20
6:14 PM GMT on Junio 20, 2008
i am piss with the NWS in miami,here in hialeah we have like a storm right know with a lot of winds,and no even a special statement in tv nothing!! we are humans.
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622. txalwaysprepared
6:10 PM GMT on June 20, 2008
Had fun with yesterdays tstorms in Houston, although very little rain where I actually live.

Hoping more rain today, but I don't see it.

Would love for a little bitty "Wave" to come in from the GOM and drench us!! :) Any chances?
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619. melwerle
6:09 PM GMT on June 20, 2008
Anyone know if we're supposed to have another wave of tstorms today in the southeast? Starting to cloud over a bit...
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618. Floodman
1:04 PM CDT on June 20, 2008
John, Johnny, Joe, James

I'm not going to ask which one...it wouldn't be polite, as no one has asked mine...and it's not Jerry LOL

Yeah, Drak, I thought Boots was a bit out there...unless of course, you play the sax...LOL
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617. weathermanwatson
6:02 PM GMT on June 20, 2008
Moisture is beginning to increase in the GoM.
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615. Floodman
12:59 PM CDT on June 20, 2008
610. JLPR

An area of 30knts+ west of the wave, and dry air right in front of it; this one has some work to do (or a little bob and weave) if it's going to amount to much other than a rain event
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614. Drakoen
5:58 PM GMT on June 20, 2008
612. Floodman 5:53 PM GMT on June 20, 2008
588. Weather456

Boots Drakoen?

I have no idea what he's talking about either.
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613. Floodman
12:55 PM CDT on June 20, 2008
597. jphurricane2006

Jack? Jacko?
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612. Floodman
12:51 PM CDT on June 20, 2008
588. Weather456

Boots Drakoen?
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611. yamil20
5:49 PM GMT on Junio 20, 2008
Link

latest wind shear map
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610. JLPR
5:46 PM GMT on June 20, 2008
umm the west Caribbean and the Gulf of Mexico are good fo the wave considering the high TCHP there =O But wind shear appears to be a problem in the West Caribbean
anyone has a map or something that forecasts shear in that area?
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609. WeatherfanPR
5:43 PM GMT on June 20, 2008
yes JLPR it's a fighter. I think this wave at 64w wants to develop since it came out of Africa and now is entering the Caribbean Sea and then maybe the Gulf of Mexico so it has some chances to develop before dying.
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608. 69Viking
12:36 PM CDT on June 20, 2008
604. jphurricane2006

The message I received is that the website was overloaded! Blog Overload everyone!
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607. JLPR
5:36 PM GMT on June 20, 2008
I believe so JP =P couldnt enter WU for a moment
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606. Drakoen
5:35 PM GMT on June 20, 2008
did we break wunderground?
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605. JLPR
5:34 PM GMT on June 20, 2008
yup decent showers in Carolina with the wave =)
My plants are happy =D

I see this tropical wave develop some extra convection during night =O
This one sure is a big fighter no matter what it keeps going and going
like the energizer bunny 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.