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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704. pottery
6:13 PM AST on June 20, 2008
...But where is my new image then ?? Huh ?!!
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703. pottery
5:01 PM AST on June 20, 2008
OK, I got it worked out.
Thanks for the help, Skye etc.
No Drakoen, it was a grandson.
Las Cuevas beach, North Coast Trinidad.
Very nice beach, and no one is ever there !
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702. ShenValleyFlyFish
5:55 PM EDT on June 20, 2008
700. guygee

Man I'm usully in you'r corner but that post makes no sense at all. Show me one state besides California or Florida that that has more land in agracultural production than 50 yrs ago. I am so tired of the agrucultural sector catching the hell for the change in the landscape that is driven by the change in national life style. Do you suburbanites really think that your way of life is sustainable? Engineering principles, LMAO. How much food did you produce for a hungry world this year?
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701. pearlandaggie
9:49 PM GMT on June 20, 2008
i sure hope this pans out!

Emerging Solar Panel Technology
Member Since: September 14, 2007 Posts: 3 Comments: 3963
700. guygee
9:44 PM GMT on June 20, 2008
655. NoMeteorsInOlogy 8:25 PM GMT on June 20, 2008
Comment on the 500 year storm (above, from Doc)and climate change.

A little known fact: ditches on roadsides in Virginia are built to a depth that is supposed to be able to handle what is categorized as a 50 year storm....

I think anyone watching the former development boom around the country must have noticed that when housing developments were being put into flood zone areas, there were always corresponding changes to the drainage system that included stormwater retention ponds designed to hold the excess water due to the land use change. The same goes for highway improvement projects or any other development in the flood plain. These efforts are mandated by FEMA's No Rise policy, plus possibly even stricter local regulations.
The policy is a matter of law as set forth is U.S Code Title 44,Ch.I,Subchapter B,Part 60--CRITERIA FOR LAND MANAGEMENT AND USE. The basic goal is that development should result in no rise in the elevation of the floodplain.

What is staggering is that the sound principles of engineering for floods that were applied to residential and other types of development were not applied to agricultural development. This is one the main contributing factors to the floods according to Dr. Masters' blog post, above. Since agricultural development results in increased run-off and raising of the floodplain, requirements for emergency storm drainage systems and stormwater retention ponds could have done much to help avert or at least mitigate the disaster. It is hard to believe that these consequences could not be foreseen by those highly trained professionals in the field. Why sound stormwater engineering practices that are so well-known and widely applied to residential and other types of development were not applied to agricultural development should be a matter of investigation by the authorities, under demand of the citizens who are suffering the disastrous consequences.
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698. Drakoen
9:33 PM GMT on June 20, 2008
696. jphurricane2006 9:32 PM GMT on June 20, 2008
shhh Drak lets not speak of the ill please lol


lol yea. Put that drama to the back-burner so to speak.
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697. smmcdavid
4:32 PM CDT on June 20, 2008
I should have known Drak... on that note, see you guys later!
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695. thelmores
9:32 PM GMT on June 20, 2008
yea...... but its too big to be a pin-hole! LOL
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694. Drakoen
9:28 PM GMT on June 20, 2008
Fengshen gained back it's eye:
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693. thelmores
9:27 PM GMT on June 20, 2008
pottery, your Avatar, the beaches kook exactly like here is South Carolina..... must be all that volcanic sand.....
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692. Drakoen
9:28 PM GMT on June 20, 2008
690. smmcdavid 9:26 PM GMT on June 20, 2008
Hi all!

Tropics still quiet, huh?


The political drama is the only thing active today.
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691. thelmores
9:22 PM GMT on June 20, 2008
678. Floodman
I told myself at 19 I'd live fast and die young.


I used to say the same..... now like you, I have 2 discs in my neck, and 2 in my lower back that are prolapsed.....

so far I have chosen beer and an ocassional pain killer over "recommended" surgery..... with all those years of medicalo training..... what do they know! LOL
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690. smmcdavid
4:25 PM CDT on June 20, 2008
Hi all!

Tropics still quiet, huh?

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689. Drakoen
9:23 PM GMT on June 20, 2008
pottery is that you surfing?
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688. thelmores
9:09 PM GMT on June 20, 2008
nice thunderstorm here in Myrtle Beach about 1.5 hours ago...... we got an inch of rain in about 30 minutes..... it was pouring!

no complaints here, now I don't have to water the lawn! yaay!

Plus when lightening strikes, more computer repairs for those who don't take the proper precautions......
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687. Skyepony (Mod)
9:16 PM GMT on June 20, 2008
pottery~is that the avatar you wanted?
Member Since: August 10, 2005 Posts: 226 Comments: 39398
686. Floodman
4:12 PM CDT on June 20, 2008
Thanks, dude! Well, folks, I'm out...BBL
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685. MonkeeInDaTrunk
2:11 PM PDT on June 20, 2008
I have some bacon that might make you feel better, Jerry, but I'm afraid to post it in this blog! Maybe if I found some bacon that looked like a pinhole eye!!
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684. stormdude77
5:05 PM AST on June 20, 2008
Afternoon all

I hope all turns out well with you, Flood!
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683. Floodman
4:07 PM CDT on June 20, 2008
I only ever take as much as I need...
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682. Floodman
4:02 PM CDT on June 20, 2008
Yep, Monk...I don't do well in really TIGHT spaces
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681. MonkeeInDaTrunk
2:03 PM PDT on June 20, 2008
just take it easy on the meds, Jerry....you old hippie, you....

;)
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680. Floodman
4:01 PM CDT on June 20, 2008
Thanks for asking, folks...the best people come in here
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679. pottery
5:00 PM AST on June 20, 2008
Anyone here knows how to change an existing avatar ??
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678. Floodman
3:59 PM CDT on June 20, 2008
The usual suspect...I told myself at 19 I'd live fast and die young...I did the first part but forgot about the last; some disk issues, a little arthritis and *POOF* there you go, a script for pain, a script for muscle spasm, and the occasional irradiation to see how bad it's gotten...I'll live (I hope) LOL
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677. pottery
4:57 PM AST on June 20, 2008
Hope all is well, Flood.
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676. MonkeeInDaTrunk
1:56 PM PDT on June 20, 2008
MRI???


:(
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675. tiggeriffic
8:55 PM GMT on June 20, 2008
hope nothing serious, I say a prayer for ya tho...
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674. Floodman
3:54 PM CDT on June 20, 2008
Maybe...got an MRI later...claustrophobia makes me med heavily...I'll try!
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673. pottery
4:52 PM AST on June 20, 2008
I know what you mean about the lightening Tigger. We lost a 100' tree in the garden a few years ago. Just 60' from the house. Blew it to splinters. Scary power man.
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672. tiggeriffic
8:53 PM GMT on June 20, 2008
not bad flood, be back later, lightning bad, you be on later?
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671. tiggeriffic
8:52 PM GMT on June 20, 2008
ok, lightning bad now, gonna go
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670. Floodman
3:51 PM CDT on June 20, 2008
Howdy, Tig! How you been?
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669. tiggeriffic
8:50 PM GMT on June 20, 2008
Don't mind the rain, just don't like the lightning and all that goes with it.
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668. pottery
4:49 PM AST on June 20, 2008
Yeah DDR. 'nuff respect to the rain gods........
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667. DDR
8:44 PM GMT on June 20, 2008
Hey pottery
Lots of rain today,flash floods in arima and it looks like we'll get some in a while again.
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666. tiggeriffic
8:45 PM GMT on June 20, 2008
Yeah, we had a bad one Tuesday night and lost power, got another one coming thru now...and you know the rest, LOL
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665. pottery
4:43 PM AST on June 20, 2008
Good enough Tigger.

Today, it rained and it rained and it rained . You know the rest LOL
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664. tiggeriffic
8:42 PM GMT on June 20, 2008
Hey pottery, new Pic! How goes it?
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663. tiggeriffic
8:41 PM GMT on June 20, 2008
Flood! What up? You still here?
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662. pottery
4:34 PM AST on June 20, 2008
Long time no see, Tigger...
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661. tiggeriffic
8:39 PM GMT on June 20, 2008
ooohh, pretty good storm brewing up here in Charleston, hope we don't lose power again today and boot me off the puter again. Just figured I'd see what the blog is up to today.
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660. tiggeriffic
8:38 PM GMT on June 20, 2008
so is the blog acting up or did everyone leave?
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659. all4hurricanes
7:39 PM GMT on June 20, 2008
I read an article on Bush's visit to Iowa basically he says you'll be OK
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658. tiggeriffic
8:35 PM GMT on June 20, 2008
just bouncin in for a few
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657. pottery
4:27 PM AST on June 20, 2008
Nice showers all day long from the Island trop. Wave. 16mm ( .6") so far. Most of the heavy stuff has passed north and south of me, shut down the helicopter flights at the airport for 2 hrs.
We should get to 1" by the time this blows through.
My cisterns are joyfully gurgling away............

Whats next ??
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656. weatherboyfsu
8:24 PM GMT on June 20, 2008
We have a 20% chance of rain here in western orlando area.......I believe that the NWS is just off a little on their predictions.....per the radar....


Link
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655. NoMeteorsInOlogy
8:16 PM GMT on June 20, 2008
Comment on the 500 year storm (above, from Doc)and climate change.

A little known fact: ditches on roadsides in Virginia are built to a depth that is supposed to be able to handle what is categorized as a 50 year storm. I worked with planners in Virginia in '97, and they laughed that 50 year storms now happen every five years. The eldest member of the department said that 50 year storms were increasing in frequency and intensity since he began working in planning in the early seventies.

I wonder why the discource that surrounds climate change rarely includes professionals with these kinds of informed opiuions in the news? Maybe just an oversight, but it is almost comic when the news declares that "many scientists" say one thing, but, of course there are always "dissenting voices", but we never get an idea of scope. For example, do 498 scientists think we have climate change and ten don't?

Loius Black cracked that he hated television because it places two people down as opposing viewpoints, when the truth often is that one rep=resents less than 1% of informed professionals and the other represents 99% of them, but, vuisually and in time allowed to speak, they are equals--and that skews the ability to be informed terribly.

Just a thought....

:)
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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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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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