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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1154. presslord
2:44 AM GMT on June 22, 2008
My pwr out for 2 hrs on Johns Island due to storm. We`re headed to boat.to crank uo genny....and AC
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1153. JLPR
2:49 AM GMT on June 22, 2008
yes it appears to be the tropical wave looking at the model the area thats moves over PR comes from the east from where our tropical wave is
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1152. THUNDERPR
2:46 AM GMT on Junio 22, 2008
Link
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1151. sarepa
2:45 AM GMT on June 22, 2008
hmm is the twave on eatl getting better organized or loosing convection?
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1150. JLPR
2:40 AM GMT on June 22, 2008
maybe I havent nam watched the model yet
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1149. THUNDERPR
2:33 AM GMT on Junio 22, 2008
`JLPR the nam model showing 40kts winds at 850 mb over puerto rico in 48 hours in the last runs. what cause this strongs winds over us that is the catl wave.
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1145. JLPR
2:29 AM GMT on June 22, 2008
nice to meet you too =)
Well pueden hablar espaƱol =)
solo den traducciones para que nadie se nos pierda =)
---------------
Well you can speak Spanish =)
just give transduction so no one gets lost =)
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1143. TampaSpin
10:26 PM EDT on June 21, 2008
For the Spanish bloggers that are bilangual i do respect you all very much. But, out of respect to us that are not i hope you could understand......One thing that Freak pointed out is probably true is maybe some spanish bloggers don't speak English.....unfornately i don't know of a spanish blog like this but, it could be a pot of gold for someone to start.....lol
Member Since: September 2, 2007 Posts: 179 Comments: 20448
1142. THUNDERPR
2:27 AM GMT on Junio 22, 2008
yeah JLPR nice to meet you.
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1141. yamil20
2:25 AM GMT on Junio 22, 2008
i am apologise everyone,lets continuing talking in english,sorry
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1140. JLPR
2:26 AM GMT on June 22, 2008
yay! puertoricans on the blog =P
i am from Puerto Rico too =)
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1139. THUNDERPR
2:25 AM GMT on Junio 22, 2008
Es cierto yo tambien hablo espanol aca desde puerto rico. Im speak spanish im from puerto rico.
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1137. barbadosjulie
2:23 AM GMT on June 22, 2008
its ok i just like to know what others are thinking about the weather and i unfortunately don't speak Spanish. Thanks for understanding :)
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1135. FLWeatherFreak91
10:18 PM EDT on June 21, 2008
I think they should rewrite the post that was put in spanish into english......for translations purposes......or stop posting in spanish.......
Action: |


Um... ok. I'll stop writing in Spanish... but I am willing to bet that at least 50% of the people on this blog speak Spanish.. and I'm sure there are a few living in the Caribe that don't speak English at all. Plus, the blog is really slow so it doesn't matter TOO much
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1134. barbadosjulie
2:15 AM GMT on June 22, 2008
I am not bashing anyone language just would like to know there opions on the weather and unfortunately, i don't speak Spanish. Sorry guys
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1133. TampaSpin
10:13 PM EDT on June 21, 2008
1130. barbadosjulie 10:10 PM EDT on June 21, 2008
Hi guys, can anyone help with all of the Spanish post? Anyone speaks Spanish?


I think they should rewrite the post that was put in spanish into english......for translations purposes......or stop posting in spanish.......
Member Since: September 2, 2007 Posts: 179 Comments: 20448
1130. barbadosjulie
2:08 AM GMT on June 22, 2008
Hi guys, can anyone help with all of the Spanish post? Anyone speaks Spanish?
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1128. kmanislander
1:56 AM GMT on June 22, 2008
456

Whatever vorticity there is does not bear mentioning IMO.

Nearly every TWave has " broad low to mid level turning ". That's why they are called TWaves !
Member Since: August 19, 2006 Posts: 0 Comments: 15948
1126. Weather456
9:49 PM AST on June 21, 2008
No probs Cone

BBL
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1125. Weather456
9:44 PM AST on June 21, 2008
There is some level of vorticity along 35W-37W with this wave at 850 mb and 700 mb.

Also satellite imgagery showed some level of turning.

And this is what the NHC said at 8pm:

...TROPICAL WAVES...
TROPICAL WAVE IS ALONG 36W S OF 16N MOVING W NEAR 20 KT. BROAD
LOW-MID LEVEL CYCLONIC TURNING IS EVIDENT ON SATELLITE IMAGERY.
UPPER LEVEL FEATURES CONTINUE TO KEEP MOST OF THE CONVECTION W
OF THE AXIS. SCATTERED MODERATE TO STRONG CONVECTION IS FROM
4N-10N BETWEEN 35W-42W.


Member Since: July 24, 2005 Posts: 407 Comments: 19076
1124. Orcasystems
1:46 AM GMT on June 22, 2008
I am not sure.. but I think I killed the Blog??
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1123. InTheCone
9:38 PM EDT on June 21, 2008
1115.

That was an excellent analysis 456 - thanks!!
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1121. kmanislander
1:35 AM GMT on June 22, 2008
For the moment the Atl wave is just a bunch of showers. No vorticity at any level.

I am watching to see if the high overhead expands Westward in tandem with the wave.

It has lifted a bit to the North today so this one could stand a chance. First we would need to see a surface low develop and at the moment there is no evidence at all of that.

The deep convection has hung around for over 12 hrs during the diurnal minimum so let's see what happens tonight.
Member Since: August 19, 2006 Posts: 0 Comments: 15948
1120. Orcasystems
1:30 AM GMT on June 22, 2008
I have a question Storm W and a few other. My B in Law is sailing his Boat in the VicMaui 2008 Race. They cross the starting line and 10 am Pacific time Sunday.

There are two routes they can use, but normally they sail almost due south and hang a right toward Hawaii around San Diego or Baha.

The other route is the Northern Circle (Seldom used but much shorter)

Question: Which is the route to take this year, and what will the weather be like on the southern route... and will the present west coast invest have any effect on them?
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1119. Weather456
9:26 PM AST on June 21, 2008
1118. 305st0rm 9:25 PM AST on June 21, 2008
456....now is that High forecast to remain in position the next couple of weeks or months


The exact position cannot be accurately forecast but we have been observing a Negative NAO as expected and this is to continue into atleast July.

A Negative NAO favors a Azores high that is weaker than normal in the Central Subtropical Atlantic.

One thing I notice, there has not been vigorous frontal actvity for June.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1118. 305st0rm
1:24 AM GMT on June 22, 2008
456....now is that High forecast to remain in position the next couple of weeks or months
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1115. Weather456
9:17 PM AST on June 21, 2008
1113. 305st0rm 9:16 PM AST on June 21, 2008
why is the EATL so active so early


Normally, cooled upwelled waters of the EATL keep tropical waves in check as they exit, they barely get pass 20W with significant convection.

This year is different...during the winter/spring of 2007-2008, the High shifted westward than normal. This reduced the effects of the cold Canary current and ehanced warm southerly flow and downwelling leading to a significant increase in SSTs in that region.

The result is, the tropical waves are able to maintain convection further west than normal for this time of year due to these warm SSTs.

Another factor is above average rainfall of the ITCZ and Sahel.

Member Since: July 24, 2005 Posts: 407 Comments: 19076
1113. 305st0rm
1:15 AM GMT on June 22, 2008
why is the EATL so active so early
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1112. JLPR
1:13 AM GMT on June 22, 2008
lol =) I just hope nothing like that happen this season but since I am right in the middle of the ocean its not impossible =P
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1111. Weather456
9:11 PM AST on June 21, 2008
1109. JLPR 9:09 PM AST on June 21, 2008

lol...the nightmares return...lol
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1110. Weather456
8:56 PM AST on June 21, 2008
Had this tropical wave existed one week from today...it would of stand of better chance, that is why, I monitoring Africa, for next two tropical waves. The 1 week GFS showed the jet of westerlies shifting northwards due broad scale upper ridging leaving a large area of low shear across the TRP Atlantic but still high over the ECARIB. This seems fair. As for the medium/long-range GFS 1-2 weeks...wind shear remains favorable across the TRP Atlantic along with the SW North Atlantic (Bahamas and SE US), while unfavorable in the Caribbean/Gulf. This seems fair for the Trp Atlantic and SW NATL but with the passage of the MJO, I doubt wind shear will be that significant in the Gulf and WCARIB.

315K PV forecasts, a tropical wave will be situated over the EATL in 84 hrs time while it also showed a vigorous tropical wave currently over EAFRICA. The latter is similar to an August African Wave...Ouch.


I dont see any reason for atleast one named storm in July. And if that doesnt happens, then I fear an August similar to 2004 and 2007, when all conditions and the warming water (due to lack of storms in June & July) release to produce few but powerful storms.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1109. JLPR
1:07 AM GMT on June 22, 2008
yep stromdude once something looks interesting in the Catl I get into red alert lol =)

I certainly dont want anything like this:
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1108. yamil20
1:06 AM GMT on Junio 22, 2008
good evening jfv,si todavia me falta como como dos semestres mas,do you know something about how the shear is created or where can i find some info?
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1107. stormdude77
9:02 PM AST on June 21, 2008
Another impressive Twave in the CATL. I think we here in the Eastern Caribbean should be on ''high alert'''...especially since it's only June, and the tropical wave train is already in full flow
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1106. JLPR
1:04 AM GMT on June 22, 2008
The tropical wave at 36W sure looks interesting and it may get even more interesting after D-Max tonight so anyone thinks this could get to invest status?
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1104. moonlightcowboy
7:59 PM CDT on June 21, 2008
Stormdude, that sounds reasonable. Unless, there's a sneeker (and there could be), I'm not looking for any activity until about mid-July.
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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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