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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1354. rainraingoaway
8:57 AM CST on June 22, 2008
Good morning all.

Nice pics txalways. Sure was some spooky weather yesterday. We had hail and some fierce winds. Limbs down around town. Finally got 3/4 inch of rain. Hooray! Through all the mess around Houston the past few days thats all my little town has gotten.

See a blowup in the BOC. Another blob?
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1353. catastropheadjuster
2:56 PM GMT on June 22, 2008
ST a professional- LMAO that is the biggest joke i have heard all day. Just my $.02 worth.
Well how's the tropics look? Anything interesting going on out there. I take it from what most say the rest of june will be quite. I wish all season would and not cause no heart ache. I think we all have been through enough.
Sheri
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1352. guygee
2:56 PM GMT on June 22, 2008
My ignore list has zero entries. Really, STORM* is less unintelligent than he is troll. At least he is not a paid shill, which is what I think of a couple of newer posters here who do not seem so much interested in the tropics or weather as they are in politics.
Member Since: September 16, 2005 Posts: 0 Comments: 3200
1351. aquak9
10:56 AM EDT on June 22, 2008
HAH! I just called StormTop. The REAL one.

"Imitation is the sincerest form of flattery"...that's about as poetic as he gets.

Nice try, STROMTOP.
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1350. atmoaggie
2:49 PM GMT on June 22, 2008
I think once a week we should all refrain from posting...

How about we ALWAYS refrain from posting anything in response. If completely ignored he would get bored and go play in his room with his legos.
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1348. aquak9
10:52 AM EDT on June 22, 2008
Now ya'll know...STROMTOP ain't the real Stormtop. Not quite sure who it is, but it ain't him.

Accept no substitutes, hahahaha
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1347. hurricane23
10:49 AM EDT on June 22, 2008
Morning!

Interesting to note if the current SOI trend continues it could be a sign that the atlantic basin may not be to far away from coming to life.With an MJO pulse set to move in about 2 week time frame things might get interesting.

We'll see. Adrian
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1346. atmoaggie
2:48 PM GMT on June 22, 2008
Gee, thanks for quoting the ignored poster. I/we really appreciate it.
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1345. thelmores
2:43 PM GMT on June 22, 2008
I think once a week we should all refrain from posting, and let STORMTOP and all his alter ego's to have at it. Not sure about informative, but certainly entertaining! LOL
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1343. CaneAddict
2:40 PM GMT on June 22, 2008
1337. STROMTOP 2:36 PM GMT on June 22, 2008
THE VERY LEARNED STORMW HAS ISSUED A PREDICTION ALONG WITH MINE THAT WE WILL LIKELY SEE AN UPTICK IN TROPICAL ACTIVITY IN THE RANGE OF JULY 10 -- OR THEREABOUTS.

THE INFORMATION COMING IN TO MY WEATHER OFFICE INDICATES THAT THIS IS GOING TO BE A PARTICULARLY ACTIVE YEAR FOR THE GOMEX, PARTICULARLY LATER IN THE SEASON.

FORECASTER // STROMTOP


EDITED:

IGNORE MY FORECAST AS THEY ARE NOT COMING FROM MY WEATHER OFFICE, THEY ARE BEING RETRIEVED FROM MY TOILET BOWL.

FORECASTER//STROMTOP!
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1342. pearlandaggie
2:40 PM GMT on June 22, 2008
i'll stick with the Magic 8-Ball...


"it is a possibility"

LOL
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1341. Patrap
9:38 AM CDT on June 22, 2008
Been all over NOLA,..never seen a Weather Office with that here..either
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1340. Patrap
9:38 AM CDT on June 22, 2008
I'll stick with Bob Breck and the NHC/NOAA tyvm
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1339. IKE
9:37 AM CDT on June 22, 2008
Thanks for the update STROMTOP...I couldn't have made it through the day without your expertise.

Memo to STROMTOP: Pleeze unlock your caps key.
Member Since: June 9, 2005 Posts: 23 Comments: 37860
1338. Patrap
9:37 AM CDT on June 22, 2008
Wow,..now there some insight.

LOL
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1336. XoendHoroeken
10:31 AM EDT on June 22, 2008
Re; 1331

I'm in Odessa (hillsborough side)
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1335. pearlandaggie
2:21 PM GMT on June 22, 2008
too funny, pat! :)
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1334. severstorm
10:21 AM EDT on June 22, 2008
patrap your to much LOL
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1333. pearlandaggie
2:19 PM GMT on June 22, 2008
see what i mean? LOL

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1332. Patrap
9:20 AM CDT on June 22, 2008
I was thinking of using a frame from my last colonoscopy for an avatar,..

..butt I thought again.,folks might think I was a Politician.

LOL!!!!!
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1331. severstorm
10:08 AM EDT on June 22, 2008
XoendHoroeken,where abouts are you near tampa i'm in z-hills you all got lots of rain yesterday i only got .22 in
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1330. txalwaysprepared
2:17 PM GMT on June 22, 2008
1328. yeah TampaSpin thought it was a little demonic LOL

1327. Not a terrible amount, but a good dose. Would love some more.

1326. Thanks. Not the best, but I was in a hurry LOL
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1329. pearlandaggie
2:13 PM GMT on June 22, 2008
1325. LOL...almost looked like something out of a Dali painting! ;)
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1328. thelmores
2:13 PM GMT on June 22, 2008
1325,

yea, figured that was what it was, but at first glance, you have to admit, kinda eerie! LOL
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1327. pearlandaggie
2:11 PM GMT on June 22, 2008
1321. looked at your pics...that's about what we had here, too. it got REALLY dark there for a while, then sun again! i guess you guys got some fairly significant rain?
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1326. aquak9
10:12 AM EDT on June 22, 2008
1321- great pics- thanks for sharing them!
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1325. txalwaysprepared
2:11 PM GMT on June 22, 2008
LOL it's a 3D ultrasound pic of my youngest son, taken last summer. I need to change it :)
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1324. Patrap
9:07 AM CDT on June 22, 2008
GOES WV Big Pic loop of the Atlantic Basin Link
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1323. thelmores
2:06 PM GMT on June 22, 2008
1312, you have your opinion, I stated mine..... no further dialogue required as far as I am concerned! :)
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1322. pearlandaggie
2:06 PM GMT on June 22, 2008
1321. oh, cool! btw, that is that picture in your avatar? i've looked at it before and i don't recognize it...
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1321. txalwaysprepared
2:04 PM GMT on June 22, 2008
Knew they were torandao clouds so I made the kids play in the closet, just in case LOL.

I put some pics up on the wunderphotos section
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1320. surfmom
2:03 PM GMT on June 22, 2008
Thank you #1312
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1319. XoendHoroeken
10:04 AM EDT on June 22, 2008
There so fairly significant wx heading toward my area now. Hopefully I can get some footage like I did yesterday.
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1318. pearlandaggie
2:01 PM GMT on June 22, 2008
1314. that's two or three days in a row with some real gullywashers! LOL it's nice to have the rain, but my grass is like six inches tall! it should be fun to try to mow it today, assuming things stay dry.

did you guys fare alright?
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1317. presslord
9:58 AM EDT on June 22, 2008
"xenophobic"...is a mighty big word for a Gamecock to be using...

...but accurate, in this case....:)
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1316. IKE
8:58 AM CDT on June 22, 2008
SSD and their repeated satellite issues. A daily occurrence.
Member Since: June 9, 2005 Posts: 23 Comments: 37860
1315. pearlandaggie
1:57 PM GMT on June 22, 2008
1312. there's no need to generalize like that.
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1314. txalwaysprepared
1:53 PM GMT on June 22, 2008
pearland - you made it thru the storms yesterday?

Myles - true.
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1313. IKE
8:54 AM CDT on June 22, 2008
1308. msphar 8:49 AM CDT on June 22, 2008
Patrap - sign language: If two fingers means two beers universally, that begs the question what one finger means...


Screw the 2 bottle beers...just get me one quart...and if you can't do that then * you.LOL.
Member Since: June 9, 2005 Posts: 23 Comments: 37860
1312. thelmores
1:56 PM GMT on June 22, 2008
glad I missed the language flap.....american's are so xenophobic at times....

we should be honored in this blog to receive new visitor's no matter their language or origin.....

I think Dr. Masters would be disappointed by anything less.....

no real organization yet..... but impressive...

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1311. HurricaneMyles
1:49 PM GMT on June 22, 2008
melwerle - To early to say with any kind of accuracy. Timing off troughs/fronts pushing through the US would determine if it was pulled up the East Coast or up the heart of the Gulf Coast.

txalwaysprepared - It's more likely with a strong high like there is now, but it's always pretty unlikely for a tropical cyclone to run into S. America.
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1310. pearlandaggie
1:49 PM GMT on June 22, 2008
1304. there are not stupid questions...only stupid looks and stupid answers! LOL
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1309. presslord
9:48 AM EDT on June 22, 2008
Thought to be about 700 souls...

Ferry With Hundreds Capsizes in Typhoon
By PAUL ALEXANDER,AP
Posted: 2008-06-22 09:28:31
Filed Under: World News
MANILA, Philippines (June 22) - Hundreds of passengers were feared trapped and may have died after their ferry capsized in the Philippines during Typhoon Fengshen, said two survivors who struggled to shore Sunday.


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1308. msphar
1:45 PM GMT on June 22, 2008
Patrap - sign language: If two fingers means two beers universally, that begs the question what one finger means...
Member Since: August 20, 2006 Posts: 0 Comments: 289
1307. CAT4atmydoor
1:28 PM GMT on June 22, 2008
Let's not forget Punta Gorda/Port Charlotte who are just now seeing the light at the end of the Hurricane Charlie tunnel...another hit here and the population would take a nosedive. I dont need another Cat 4 eye going over my house...
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1306. Weather456
9:35 AM AST on June 22, 2008
Oh and to clear up something else....1998 also had a negative NAO, like 2004, but 1998 wasnt like 2004. We must remembered that years similar to 2004 will not repeat 4 hurricanes into FL but rather a high centered similar to 2004. There are other factors in play.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1305. txalwaysprepared
1:41 PM GMT on June 22, 2008
Myles I was hoping you'd say it would push everything into SA before having a chance to develop. :(
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1304. melwerle
1:38 PM GMT on June 22, 2008
ok - enough stupid questions from me today...Panera bound for an everything bagel and a cup of coffee.

Bring on some more rain too! My lawn is finally turning green again. Gotta love those tstorms...
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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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