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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304. Weather456
12:37 AM AST on June 20, 2008
And if anyone is wondering the "plus sign" does show up on Wunder blogs. Wonder y?
Member Since: July 24, 2005 Posts: 407 Comments: 19076
303. Weather456
12:33 AM AST on June 20, 2008
300. TampaSpin 12:33 AM AST on June 20, 2008
456 so that map as long as it is 3hours that is a future forcast then....correct. thanks for your help.
Action: | Ignore User


None of the products are forecasts, just analyses.

When you use -3 hrs, you go backwards to previous products issued and to go back forward to the latest image you use 3 hrs.

If you realize, the 3 hours function becomes null when looking at the latest image and that is becuz, you cant go any further. It becomes functional when you go backwards so you can always go forward to the latest image.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
302. TampaSpin
12:33 AM EDT on June 20, 2008
Hi Stormjunkie.....thanks....i just thought it showed trend........i guess my use of the word forcast is not a good use of words. Trend would have been a better word.
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301. StormJunkie
4:31 AM GMT on June 20, 2008
lol, see, I told ya it was already answered :~)

Good answer 456

Just for the record, I love those folks at CIMSS.
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300. TampaSpin
12:31 AM EDT on June 20, 2008
456 so that map as long as it is +3hours that is a future forcast then....correct. thanks for your help.
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299. StormJunkie
4:27 AM GMT on June 20, 2008
Evening TS, 456, and, cchs

Good to see ya VT and ninja :~)

Sorry for jumping in 456, and this is likely already answered...

TS-That +3hrs is the latest available map. If you toggle back 3 hours then you use that button to get back to the latest available image. That map shows current shear and shear trend in last 24hrs if I am not mistaken.
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298. Weather456
12:26 AM AST on June 20, 2008
296. TampaSpin 12:26 AM AST on June 20, 2008
456 at this site....Link


Oh....

-3 hours - you can look at previous maps issued.
3 hours is the next map issued.

It is useful for looking at changes in the products issued by the CIMSS, which are issued every three hours.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
297. JLPR
4:25 AM GMT on June 20, 2008
umm all the tropical waves are looking nice once they exit Africa =O I hope this trend ends soon =)
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296. TampaSpin
12:25 AM EDT on June 20, 2008
456 at this site....Link
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295. Weather456
12:24 AM AST on June 20, 2008
292. TampaSpin 12:15 AM AST on June 20, 2008
456 question on that shear map i posted it has -3hours and 3hours.....what does that mean i guess im as confused as riding a street bike in a severe thunderstorm.......lol


On the map or on the web page?
Member Since: July 24, 2005 Posts: 407 Comments: 19076
294. Weather456
12:08 AM AST on June 20, 2008
The surface front dissipated into a surface trough as expected.



Tropical Wave

Correction: the map should read June 19



Member Since: July 24, 2005 Posts: 407 Comments: 19076
293. Littleninjagrl
12:19 AM EDT on June 20, 2008
LOL TampaSpin! POWERSLIDE!!!!!!!!!!!!!!
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292. TampaSpin
12:13 AM EDT on June 20, 2008
456 question on that shear map i posted it has -3hours and 3hours.....what does that mean i guess im as confused as riding a street bike in a severe thunderstorm.......lol
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291. TampaSpin
12:06 AM EDT on June 20, 2008
284. Littleninjagrl 11:54 PM EDT on June 19, 2008
tampaspin....sport bike + rain = bad news. your right about that.


I use to powerslide with my dirt bike. Will that work.........lol
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290. TampaSpin
12:01 AM EDT on June 20, 2008
Thanks 456
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289. Weather456
12:01 AM AST on June 20, 2008
286. cchsweatherman 12:00 AM AST on June 20, 2008
Good night all.

456- I don't know if you'll cover this in your Special Updates coming in the very near future, but is there a direct correlation between the MJO and wind shear? Could you message me the answer? It seems to me that there is a direct correlation, but just want to hear your opinion. Thanks.


Yep, there is a direct correlation, but its more associated with the active pulse.

MJO active pulse, surface convergence, upward motion, upper level divergence or ourflow (low shear)

MJO inactive pulse over the Atlantic, enhance convection over the EPAC, ehance outflow and westerlies over the Atlantic. MJO inactive pulse, enhance convection over African continent, enhance outflow and easterlies over the Atlantic.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
288. listenerVT
11:52 PM EDT on June 19, 2008
Shear ahead of the wave looks pretty strong.

http://cimss.ssec.wisc.edu/tropic/real-time/atlantic/winds/wg8shr.html
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287. Weather456
11:59 PM AST on June 19, 2008
CCH is correct.

Tampa...try this link
Member Since: July 24, 2005 Posts: 407 Comments: 19076
286. cchsweatherman
11:58 PM EDT on June 19, 2008
Good night all.

456- I don't know if you'll cover this in your Special Updates coming in the very near future, but is there a direct correlation between the MJO and wind shear? Could you message me the answer? It seems to me that there is a direct correlation, but just want to hear your opinion. Thanks.
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285. cchsweatherman
11:54 PM EDT on June 19, 2008
Tampa - Remember that is not the forecasted shear, rather the difference in shear from 24 hours ago. Make sure you interpret your maps and graphs correctly. On that map, it indicates wind shear is 20kts lower over the Bahamas than 24 hours ago, while shear is 10kts higher over the wave. This does not mean that it will keep that way.
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284. Littleninjagrl
11:53 PM EDT on June 19, 2008
tampaspin....sport bike + rain = bad news. your right about that.
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283. TampaSpin
11:47 PM EDT on June 19, 2008
Shear in the Bahamas is low and forcast to improve in the Bahamas. Shear in the Carribean is about 30kts. and forcast to increase in shear.
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282. Weather456
11:45 PM AST on June 19, 2008
266. BahaHurican 11:03 PM AST on June 19, 2008

I mentioned that area on my blog. Gonna monitor it just incase it tries to sneak up.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
281. pottery
11:43 PM AST on June 19, 2008
LOL Tampa. I'm relieved to know I'm not alone.
I'll have to try and figure it all out in the morning, its 11:45 here
Stay safe everyone
Member Since: October 24, 2005 Posts: 0 Comments: 24906
280. stormdude77
11:39 PM AST on June 19, 2008
The Twave in the EATL (25W, 8N) looks fairly well in structure and organization, and even convection wise. The CMC models tries to develop this wave, in another two days or so...and yes, I know it's the CMC, LOL...but still something to keep an eye on



Anyway, Good night y'all...
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279. aspectre
2:53 AM GMT on June 20, 2008
250. HadesGodWyvern "...Didn't think avator had to be weather related.
252. surfmom "i did not realize that either..."

I suspect the moderator chose to disallow topless photos due to (expectable) evolution
of gender neutrality laws via "What's good for the gander is good for the goose."
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278. HadesGodWyvern (Mod)
3:43 AM GMT on June 20, 2008
Philippines Atmospheric Geophysical Astronomical Services Administration

"FRANK" has intensified into a typhoon as it endangers Eastern Visayas.

Tropical Cyclone Bulletin #7
============================
At 11:00 A.M. PST, Typhoon Frank located near 11.3°N, 126.3°E or 60 kms Northeast of Guiuan, Eastern Samar has sustained winds of 65 knots with gusts up to 80 knots.

Storm Signals Raised
====================

Warning Signal #3 (100-185 km/h)

Luzon Region
1.Masbate
2.Sorsogon
3.Albay
4.Catanduanes

Visayas Region
1.Samar Provinces
2.Leyte
3.Biliran Island

Mindanao Region
1.No Signal Raised

Warning Signal #2 (60-100 km/h)

Luzon Region
1.Camarines Sur
2.Camarines Norte

Visayas Region
1.Southern Leyte
2.Burias Island
3.Northern Cebu

Mindanao Region
1.Dinagat Island
2.Siargao Island

Warning Signal #1 (30-50 km/h)

Luzon Region
1.Romblon
2.Marinduque
3.Southern Quezon
4.Polillo

Visayas Region
1.Rest of Cebu
2.Bohol
3.Northern Negros
4.Capiz
5.Aklan
6.Northern Iloilo

Mindanao Region
1.Surigao del Norte

Note: Saturday evening, Frank is expected to landfall over Eastern Samar.

Typhoon "FRANK" is expected to enhance the southwest monsoon and bring rains over the rest of Southern Luzon, rest of Visayas and Mindanao. Residents in low lying areas and near mountain slopes are advised to take all the necessary precautions against possible flashfloods and landslides.

Likewise, those living in coastal areas under signal 2 and 3 are alerted against big waves or storm surges generated by this tropical cyclone.

The public and the disaster coordinating councils concerned are advised to take appropriate action and watch for the next bulletin to be issued at 5 p.m. today.
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277. jabjb2
3:40 AM GMT on June 20, 2008
what is the shear like out ahead of the wave in the Caribbean, cchs ?
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276. cchsweatherman
11:32 PM EDT on June 19, 2008
Good evening all! It appears that the tropical wave continues to move towards the west and remains a fighter as the low-level circulation-located at around 15N 62W based upon satellite observation) has remained intact (based upon the 850MB Vorticity Map), even in the presence of very hostile 40kt. shear. Even though there is very little, if any, chance this will develop, I'm not going to completely rule that out. Just watching this wave fight makes me think that way.
Figure 1 - 850MB Vorticity Map (Source: CIMSS)

Figure 2 - NASA IR Satellite Image for Tropical Wave (Source: NASA Satellite Page)
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275. TampaSpin
11:37 PM EDT on June 19, 2008
273. pottery 11:36 PM EDT on June 19, 2008
OK. I give up.
How to change an avatar ??


Pottery, i hear ya i have the same problem and ain't figured it out either.......lol
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274. TampaSpin
11:36 PM EDT on June 19, 2008
Ninja you couldn't ride that bike of yours fast in the rain....lol
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273. pottery
11:35 PM AST on June 19, 2008
OK. I give up.
How to change an avatar ??
Member Since: October 24, 2005 Posts: 0 Comments: 24906
272. Littleninjagrl
11:24 PM EDT on June 19, 2008
its so muggy out right now. I've taken three showers already today. Wish it would rain again like it did last night! The thunder was awesome to sleep to. Love it when it rains like that.
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271. TampaSpin
11:22 PM EDT on June 19, 2008
LDog my garage could be sweep out if you would like to use my broom. LMAO
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270. Ldog74
2:59 AM GMT on June 20, 2008
Just wait till the world series Tampa, we'll be there.
Is that cold front the only thing out there with any supposed potential right now?
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269. stormdude77
11:12 PM AST on June 19, 2008
The NAM models predicts the front near the Bahamas (southern half), will break off...and develop (either tropical or sub-tropical in nature)...
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268. stormdude77
11:02 PM AST on June 19, 2008
Good evening all...great avatar Pottery! Looks very cool
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267. yamil20
3:08 AM GMT on Junio 20, 2008
good evening everyone.where this thing in the bahamas is forecast to go?
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266. BahaHurican
11:00 PM EDT on June 19, 2008
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265. pottery
10:50 PM AST on June 19, 2008
Evening all. A quiet Tropical day ?
Member Since: October 24, 2005 Posts: 0 Comments: 24906
264. jabjb2
2:55 AM GMT on June 20, 2008
where is that spin at baha?
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263. Weather456
10:53 PM AST on June 19, 2008
Tropical Update
Member Since: July 24, 2005 Posts: 407 Comments: 19076
262. TampaSpin
10:51 PM EDT on June 19, 2008
RAYS Sweep the Cubs........good evening everyone.
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261. BahaHurican
10:47 PM EDT on June 19, 2008
260. keywestdingding 10:45 PM EDT on June 19, 2008

I was looking at that and thinking maybe I was seeing a bit of a spin.
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260. keywestdingding
2:43 AM GMT on June 20, 2008
looks like the tail end of the cold front might break off and form something.
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259. atmoaggie
2:23 AM GMT on June 20, 2008
251. aspectre 1:41 AM GMT on June 20, 2008

Abita Springs wunderground forecast (with 100 feet elevation) Link

This location is ~5 miles north of I-12.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
258. BahaHurican
10:19 PM EDT on June 19, 2008
254. BoynSea 9:47 PM EDT on June 19, 2008
North Abaco, Bahamas


Evening Boyn. U guys got the rain today. First day this week we didn't. It was really humid this afternoon for the first time, also. But it's been good to have the rain. It was DRY in Nassau . . .
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257. kellnerp
10:23 PM EDT on June 19, 2008
If heavy precipitation events become more frequent and runoff becomes slightly greater then the 500 year and 100 year flood plains will have to be redefined. This will sort itself out by making it expensive insurance wise to build in some places were we presently allow building. Just hope the government doesn't come in and provide insurance in problematic areas.

Cedar Rapids is largely built on an old ox-bow in the river. Why wouldn't it flood once in a while?

As far as runoff goes, this was a bad time of year in Iowa because the corn and other crops weren't really up enough to make a difference. Iowa has made a lot of progress in retaining water on farms over the years. But in my lifetime I have seen a lot of erosion take place. It is a lot cheaper and in some ways more reliable to store the water near the source than channel it when it gets to the river. Maybe we didn't learn our lesson from the Missouri river. Channeling the flow scoured the channel and caused many other problems.

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256. KEEPEROFTHEGATE (Mod)
2:22 AM GMT on June 20, 2008
quiet in here
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255. msphar
1:44 AM GMT on June 20, 2008
CHEER the SHEAR down there in the MDR bowling alley.
Member Since: August 20, 2006 Posts: 0 Comments: 289
254. BoynSea
1:45 AM GMT on June 20, 2008
North Abaco, Bahamas

Well, be careful what you wish for! We have been under drought conditions for some time, wishing for a good rain. We got that today, plus some! The landscape and grass are very grateful, and the water cisterns are near full, but the soil is near saturation. This weather pattern began Wednesday, with a waterspout marching down our "backyard", causing no damage.

Supposed to clear out by tomorrow, that';s a good deal for us, 'cause we need to make a boat run.
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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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