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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404. IKE
8:52 AM CDT on June 20, 2008
RasBongo....bong hits? LOL...

Your link doesn't work...sorry.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
403. IKE
8:51 AM CDT on June 20, 2008
398. Weather456 8:50 AM CDT on June 20, 2008
Now if a surface low forms, and the wave is near depression status, then it will be influence by other steering elements, but as a tropical wave...it is embedded within deep easterly flow.


True.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
402. RasBongo
1:42 PM GMT on June 20, 2008
Wah gwaan everybody?

Back from a 24 hour ban. I got kick out for posting a joke.

Have you noticed on EUMETSAT that the EATL system is starting to spin around itself?


Link
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401. IKE
8:47 AM CDT on June 20, 2008
395. Weather456 8:47 AM CDT on June 20, 2008
366. IKE 12:58 PM GMT on June 20, 2008
456...I'm not so sure the wave in the Eastern Caribbean will go into Central-America. If so there must be strong high-pressure building in...I know it's suppose to, but that would be a strong one.

Where will it go then? It has no where else to go but into Central America, even if it crosses the Yucatan Channel, and enter the BOC. Also watch the steering speed. Conditions are expected to improve in the WCARIB so timing is everything.


I wasn't thinking of Mexico as Central-America. If their included...yeah, you're probably right.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
400. Buhdog
1:32 PM GMT 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.

Is this the baha flare up?
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399. Nolehead
1:47 PM GMT on June 20, 2008
i'm sorry FEMA is the biggest joke to this country...whenever our largest federal funded program just either sends the materials to other places that don't need them or either they do nothing and point fingers at other parties asking hey why haven't you done anything just does not make sence to me...
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398. Weather456
1:49 PM GMT on June 20, 2008
Now if a surface low forms, and the wave is near depression status, then it will be influence by other steering elements, but as a tropical wave...it is embedded within deep easterly flow.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
396. pearlandaggie
1:47 PM GMT on June 20, 2008
agreed, JP...sometimes the human response (or lack thereof) is FAR worse than the original disaster (see Katrina)
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395. Weather456
1:43 PM GMT on June 20, 2008
366. IKE 12:58 PM GMT on June 20, 2008
456...I'm not so sure the wave in the Eastern Caribbean will go into Central-America. If so there must be strong high-pressure building in...I know it's suppose to, but that would be a strong one.


Where will it go then? It has no where else to go but into Central America, even if it crosses the Yucatan Channel (Mexico), and enter the BOC. Also watch the steering speed. Conditions are expected to improve in the WCARIB so timing is everything.

Member Since: July 24, 2005 Posts: 407 Comments: 19076
394. IKE
8:46 AM CDT on June 20, 2008
I can modify w/IE.

FF3 is flawed.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
391. pearlandaggie
1:40 PM GMT on June 20, 2008
383. of COURSE the severity of the floods was partly due to human causes! agriculture, levees, land development, and drainage modification ALL impart a change on the hydrological consequences of a major precipitation event. however, SUVs have NOTHING to do with it whatsoever! :)
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390. Nolehead
1:41 PM GMT on June 20, 2008
ike...AMEN to that!!
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389. IKE
8:42 AM CDT on June 20, 2008
386. TampaSpin 8:42 AM CDT on June 20, 2008
Ike you shouldn't need to edit anything anyways. You never type anything wrong......lol


Right. LOL.

I'll switch over to IE and try deleting.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
387. IKE
8:42 AM CDT on June 20, 2008
It won't delete w/FF3.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
386. TampaSpin
9:41 AM EDT on June 20, 2008
Ike you shouldn't need to edit anything anyways. You never type anything wrong......lol
Member Since: September 2, 2007 Posts: 178 Comments: 20443
385. IKE
8:40 AM CDT on June 20, 2008
Thank God it's Friday.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
384. IKE
8:39 AM CDT on June 20, 2008
381. pearlandaggie 8:35 AM CDT on June 20, 2008
IKE, how does one delete a comment?


Good point...may not can even do that.

Oh well...I've got IE!
Member Since: June 9, 2005 Posts: 23 Comments: 37858
383. TampaWeatherBuff
1:39 PM GMT on June 20, 2008
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.

As if the climate is obliged to observe expectations from man-calculated statistical averages?

Maybe all these supposed anomalies are a sign our methodology for applying statistics to weather patterns is fundamentally flawed? Note how bad hurricane predictions are, that are based solely on statistical averages.

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382. TampaSpin
9:37 AM EDT on June 20, 2008
The wave entering the Carribean has held together surprising well. Its any a little better conditions, but shear appears to be high.
Member Since: September 2, 2007 Posts: 178 Comments: 20443
381. pearlandaggie
1:34 PM GMT on June 20, 2008
IKE, how does one delete a comment?
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379. fmbill
1:30 PM GMT on June 20, 2008
Good morning all.

A portion of the twave is showing up nicely on NWS radar out of PR.

NWS Radar
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377. IKE
8:24 AM CDT on June 20, 2008
373. pearlandaggie 8:10 AM CDT on June 20, 2008
nevermind, IKE...i was wrong. my BAD!


Yeah...you can't modify. You can delete and start over.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
375. TampaSpin
9:19 AM EDT on June 20, 2008
Morning everyone...
Member Since: September 2, 2007 Posts: 178 Comments: 20443
374. BahaHurican
9:15 AM EDT on June 20, 2008
OPC is suggesting that ridge is likely to stay in place and be reinforced by another high moving in from the west. I don't see much likelihood of a serious turn toward the north with this Twave.

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373. pearlandaggie
1:08 PM GMT on June 20, 2008
nevermind, IKE...i was wrong. my BAD!
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371. BahaHurican
9:04 AM EDT on June 20, 2008
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370. pearlandaggie
1:05 PM GMT on June 20, 2008
367. IKE, i'm using FF3 and the modify comment is now working for me. i used it last night a couple of times.
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369. 69Viking
8:01 AM CDT on June 20, 2008
368. IKE

Good point IKE. There's definitely a pocket of light shear for it if it takes a south Florida path. Not likely but always possible. I'm just impressed at how it has maintained itself under all the shear it has gone through. Could be trouble later in the season if systems like this keep coming and shear goes away.
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368. IKE
7:58 AM CDT on June 20, 2008
If the eastern Caribbean blob could go WNW...the shear lessens....

0900UTC CIMSS Shear Map
Member Since: June 9, 2005 Posts: 23 Comments: 37858
367. IKE
7:58 AM CDT on June 20, 2008
I can't edit it...FIREFOX 3...ugh
Member Since: June 9, 2005 Posts: 23 Comments: 37858
366. IKE
7:56 AM CDT on June 20, 2008
456...I'm not so sure the wave in the Eastern Caribbean will go into Central-America. If so there must be strong high-pressure building in...I know it's suppose to, but that would be a strong one.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
365. 69Viking
7:48 AM CDT on June 20, 2008
Good morning all! If anything it looks like the wave in the Islands is holding together enough to bring some good rains. It will be interesting to see what this wave does if the shear lightens up.
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364. IKE
7:55 AM CDT on June 20, 2008
You beat me to it BahaHurican...I'll edit it!
Member Since: June 9, 2005 Posts: 23 Comments: 37858
363. IKE
7:53 AM CDT on June 20, 2008
From the 8:05 am EDST tropical weather discussion........

"...Tropical waves...

A tropical wave is along 23w S of 12n moving W 10-15 kt. The
wave shows up very well on the tpw product and the hovmoller
diagram that clearly indicates the wwd propagation of the wave.
Low level satellite derived winds also supports the position of
the wave axis which exhibits some cyclonic turning near 7n.
Scattered moderate to isolated strong convection is mainly ahead
of the wave axis from 5n-11n between 23w-27w.

An active tropical wave is affecting the Lesser Antilles early
this morning with scattered to numerous showers...tstms and
gusty winds. Its axis is along 61w/62w S of 19n moving W 15-20
kt. A broad area of cyclonic turning is associated with the
wave. Surface observations from those islands reveal that the
wave has entered the E Caribbean. Sfc pressures are falling to
near 2 mb in this area. The mimic-tpw product shows the wave
very well where a good surge of moisture is noted. The wave is
expected to affect the UK/US Virgin Islands this morning and
Puerto Rico throughout the day...bringing an increase in
shower/tstm activity and gusty winds. The wave should reach
Dominican Republic early Saturday."
Member Since: June 9, 2005 Posts: 23 Comments: 37858
362. BahaHurican
8:46 AM EDT on June 20, 2008
From the 8:05 TWD:

AN ACTIVE TROPICAL WAVE IS AFFECTING THE LESSER ANTILLES EARLY
THIS MORNING WITH SCATTERED TO NUMEROUS SHOWERS...TSTMS AND
GUSTY WINDS. ITS AXIS IS ALONG 61W/62W S OF 19N MOVING W 15-20
KT. A BROAD AREA OF CYCLONIC TURNING IS ASSOCIATED WITH THE
WAVE. SURFACE OBSERVATIONS FROM THOSE ISLANDS REVEAL THAT THE
WAVE HAS ENTERED THE E CARIBBEAN. SFC PRESSURES ARE FALLING TO
NEAR 2 MB IN THIS AREA. THE MIMIC-TPW PRODUCT SHOWS THE WAVE
VERY WELL WHERE A GOOD SURGE OF MOISTURE IS NOTED. THE WAVE IS
EXPECTED TO AFFECT THE UK/US VIRGIN ISLANDS THIS MORNING AND
PUERTO RICO THROUGHOUT THE DAY...BRINGING AN INCREASE IN
SHOWER/TSTM ACTIVITY AND GUSTY WINDS. THE WAVE SHOULD REACH
DOMINICAN REPUBLIC EARLY SATURDAY.

I'm impressed by how far this wave has moved north. If this is the way the High is going to set up over the rest of the summer, we could have a Leewards/PR/Hispaniola hit later on. I keep noticing the 1016 isobar running somewhere through the Bahamas. . .
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361. kmanislander
12:41 PM GMT on June 20, 2008
Good morning all

Two areas of interest for the weekend. The E Caribbean wave has flared up some but the Westerlies throughout the basin are still in the 30 to 40 knot range. The 850 mb vorticity is fairly impressive but so far this wave has not been able to translate a low to the surface.

I still see little chance of development unless the forward speed slows ( which usually tends to happen just below Haiti ) and shear slackens. Here is the 850 mb map Link


The E Atl wave has an impressive structure and there is evidence of the beginnings of a circulation. So far, no low at the surface but a sharp wind shift on QS.

Catch you all later
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360. BahaHurican
8:40 AM EDT on June 20, 2008
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359. pearlandaggie
12:41 PM GMT on June 20, 2008
346. wow, 456! that's a really cool perspective. you can see why the coriolis effect comes into play. when looking at other projections, it's easy to think of the path as a straight line, but a storm's path is more like a left-handed curveball! very cool!
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358. Weather456
8:42 AM AST on June 20, 2008
357. stormdude77 8:40 AM AST on June 20, 2008
Hey W456...it's pretty windy here ths morning (especially in rain showers; does the Twave still have some kind of circulation)?


Surface obs and partial qs, sugguest not.

Posted this on my blog yestreday:

It is interesting to note that these westerlies disrupted the mid-level circulation associated with the wave, much like blowing really hard on a spinning top.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
357. stormdude77
8:37 AM AST on June 20, 2008
Hey W456...it's pretty windy here ths morning (especially in rain showers; does the Twave still have some kind of circulation)?
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356. BahaHurican
8:39 AM EDT on June 20, 2008
Check Navy site.

http://www.nrlmry.navy.mil/tc_pages/tc_home.html
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355. all4hurricanes
12:36 PM GMT on June 20, 2008
Frank/ Fengshen made its landfall in the Philippines I'm still waiting for WU to update it does anyone know the Max wind speed before landfall
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354. BahaHurican
8:29 AM EDT on June 20, 2008
Morning again. Most recent forecast track of Fengshen/Frank takes it just east of Manila, but keeps it at Cat 1. This could be a bad situation for the Philippines, since this storm looks like a gullywasher. Can u say flooding, landslides etc?

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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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