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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204. pearlandaggie
11:12 PM GMT on June 19, 2008
190. basscat71, here ya go...

Link
Member Since: September 14, 2007 Posts: 3 Comments: 3963
203. pottery
7:06 PM AST on June 19, 2008
OK. That aint working LOL
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202. pottery
7:04 PM AST on June 19, 2008
/Users/buntyoconnor/Desktop/m8trucol.jpg
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201. txalwaysprepared
10:45 PM GMT on June 19, 2008
Picture, from my phone, of the storms moving through Houston this afternoon. I got lucky and got a lightning strike lol
Member Since: August 18, 2007 Posts: 0 Comments: 1642
200. Drakoen
10:42 PM GMT on June 19, 2008
Member Since: October 28, 2006 Posts: 57 Comments: 30562
199. Drakoen
10:41 PM GMT on June 19, 2008
Nice eye wall building:
Member Since: October 28, 2006 Posts: 57 Comments: 30562
198. cybergrump
10:36 PM GMT on June 19, 2008
The blob getting ready to enter the GOM from the yucatan. Wind shear in the gulf is low can we get something out of it?
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197. HadesGodWyvern (Mod)
10:17 PM GMT on June 19, 2008
Tropical Storm "FRANK" is expected to enhance the southwest monsoon and bring rains over the rest of Mindanao and Visayas and later to Southern Luzon.

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 11 a.m. today
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196. weathermanwannabe
6:11 PM EDT on June 19, 2008
Well I'm Out and Everyone Have a Great Evening; temps expected to reach 97 tommorow in the Florida Big Bend/Panhandle and No Rain.....Yuck
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195. HadesGodWyvern (Mod)
10:11 PM GMT on June 19, 2008
Philippines Atmospheric Geophysical Astronomical Services Administration

Tropical Storm "FRANK" has gained more strength as it continues to move closer to Samar - Leyte Area

Tropical Cyclone Bulletin #6
============================
At 5:00 A.M. PST, Tropical Storm Frank located near 11.0ºN, 127.4ºE or 180 kms East of Guiuan, Eastern Samar has sustained winds of 60 knots with gusts up to 75 knots.

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

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

Luzon Region
1.No Signals Raised

Visayas Region
1.Samar Provinces

Mindanao Region
1.No Signal Raised

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

Luzon Region
1.Catanduanes
2.Sorsogon

Visayas Region
1.Leyte Provinces
2.Biliran Island

Mindanao Region
1.Dinagat Island
2.Siargao Island

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

Luzon Region
1.Camarines Sur
2.Albay
3.Burias Island
4.Masbate
5.Ticao Island

Visayas Region
1.Northern Cebu
2.Bohol

Mindanao Region
1.Surigao del Norte
2.Surigao del Sur
3.Agusan del Norte
4.Camiguin
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194. nrtiwlnvragn
6:10 PM EDT on June 19, 2008
Flood forecasting
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193. ShenValleyFlyFish
5:51 PM EDT on June 19, 2008
100 yr / 500 yr flood designations are based on geological research and are an attempt to express probabilities in a form that laymen can approach. A stream I fish had a 500 yr flood. How do they know. 500 layers of yearly soil deposit. If we had another one of the same magnitude here 10 yrs later it would still be a 500 yr food.
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192. all4hurricanes
9:56 PM GMT on June 19, 2008
So what is the actual strength of Typhoon Fengshen
is it cat 3 yet ?
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191. lowerbamagirl
9:44 PM GMT on June 19, 2008
Thx nrt. It kind of looks like my calculus course many, many years ago. All letters and very few numbers.

I do not understand this 100/500 year flood insanity. When we purchase life insurance, it is figured on tables, we all know that. However those selling it just tell us it will cost XXX. Why not the same for flood? I don't need to know the details. Tell me how much and I will make a decision. My husband is a catastrophe adjuster and sees so many people that were told they "didn't need flood insurance" because of the 100/500 flood analysis.

It seems to me that insurance agents talk people out of flood insurance even if they want it. That was my experience when we moved to our current house. My husband said "get flood insurance!" It was a federal case to get our agent to write the policy. He kept saying "you don't need it!" What's up!
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190. basscat71
9:46 PM GMT on June 19, 2008
not to change the subject, but any new word on sunspot activity and its relation to climate change?
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189. Drakoen
9:44 PM GMT on June 19, 2008
In 3 days the ECMWF will issue their seasonal forecasts with is comprised of graphics with 2m Temperatures, MLSP, Rain, and SST.
Member Since: October 28, 2006 Posts: 57 Comments: 30562
188. nrtiwlnvragn
5:38 PM EDT on June 19, 2008
186. lowerbamagirl

Temperature Conversion

Conversion Tools
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187. MNTornado
4:34 PM CDT on June 19, 2008
500 year flood?
Give me a break.
What is that being based on?
What floods do we have evidence of that happened 500 years ago in America?
Who was even here to record them?
This is like saying you can do 110 or 120 percent performance when it's only physically possible to have 100 percent. Who is coming up with this nonsense?
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186. lowerbamagirl
9:34 PM GMT on June 19, 2008
Hello all here in Wunderland! Question: I know there is a formula for converting Knots to MPH, but for the life of me I can't remember -- any help?

Also checking in from AL/FL GC (literally on the line), we did do well with our rebuilding. My only complaint is that all the beach houses "sold out" to the condo developers after Ivan and our beaches are conjested with highrises!
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185. Weather456
5:30 PM AST on June 19, 2008
I say its around a 80 knot tropical cyclone.

Curve band arc - 1.50 for a DT of 4.5

Model Expected T - no also agrees with DT 4.5

Final T-no 4.5/77 knots/966 mb.




Member Since: July 24, 2005 Posts: 407 Comments: 19076
184. Drakoen
9:30 PM GMT on June 19, 2008
Very heavy rains in that band of convection west of the eye.
Member Since: October 28, 2006 Posts: 57 Comments: 30562
183. Drakoen
9:22 PM GMT on June 19, 2008
Member Since: October 28, 2006 Posts: 57 Comments: 30562
182. Weather456
5:15 PM AST on June 19, 2008
Tropical Update and when favorable conditions are expected to return.

Thanks!

Member Since: July 24, 2005 Posts: 407 Comments: 19076
181. Stormchaser2007
9:03 PM GMT on June 19, 2008
Tno/CI Rules : Constraint Limits : NO LIMIT
Weakening Flag : OFF
Rapid Dissipation Flag : OFF


Thats not good...

Member Since: June 9, 2007 Posts: 4 Comments: 15921
180. msphar
9:02 PM GMT on June 19, 2008
Today at 57W reminds me of last year's Karen struggling to move forward but getting the door slammed in her face. Sweet!
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179. Floodman
4:04 PM CDT on June 19, 2008
176. hurricanehanna

thnx, hanna...I like him
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178. Stormchaser2007
8:58 PM GMT on June 19, 2008
.
Member Since: June 9, 2007 Posts: 4 Comments: 15921
177. Stormchaser2007
8:57 PM GMT on June 19, 2008
Uhh...well it has a well formed eye now...winds will probably be moved up to 80knots


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176. hurricanehanna
8:54 PM GMT on June 19, 2008
I feel more relieved. Thanks Floodman!!!!
BTW - love your icon!
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175. Floodman
3:50 PM CDT on June 19, 2008
melwrle, how are you today, aside from rain wet?
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174. weathermanwannabe
4:47 PM EDT on June 19, 2008
172. NWWNCAVL 4:46 PM EDT on June 19, 2008 Lol....I just "thought" I was looking at the beginning of a rather broad circulation down there when I took a quick look at the Vis Loops this afternoon (why I asked if the models predicted something down there), when, you came on and mentioned as to the floater...I thought "bingo, I finally got one!".........Oh Well.....
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173. Floodman
3:49 PM CDT on June 19, 2008
165. hurricanehanna

It would take a large number of things to happen just right for Manila to take a dead on hit...most likely the storm will recuirve before it even gets that far, not to mention it would certainly have to gain 6 or 7 degrees of latitude. Here's the projected path over the next several days:

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172. NWWNCAVL
8:41 PM GMT on June 19, 2008
u had me going for a second wannab.
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171. all4hurricanes
8:44 PM GMT on June 19, 2008
I love watching rain so much I go outside in it like I'm newscasting Hurricane Humberto. I even have my own poncho ( It doesn't help much )
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170. all4hurricanes
8:36 PM GMT on June 19, 2008

Thank You Fengshen for enrolling in West Pacific University for a total of 24 hours. Here is your degree in Extensive Rainfall and Rapid Intensification. You now have the super typhoon license allowing you to become a super typhoon within 8 hours.
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169. melwerle
8:39 PM GMT on June 19, 2008
Wow - we got hit with a MAJOR storm a little while ago - hail, tornado warnings...and to think there was like a 10% chance of rain this morning with no hazardous weather outlook...coming down again now. LOVE seeing the rain and I'm sure my lawn likes it better...
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168. 69Viking
2:30 PM CDT on June 19, 2008
116. Nolehead 2:05 PM CDT on June 19, 2008

Pensacola, you got it..local boy right here myself..think we did a damn fine job concidering the circumstances.


Been in meetings and late to add my input but don't forget Navarre, Fort Walton Beach, and Destin. They all experienced the eastern eyewall of those storms and came back with a flurry afterwards. Just look at the rebuilding in those parts now. You would never know a Hurricane hit just 3 years ago.
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167. weathermanwannabe
4:34 PM EDT on June 19, 2008
164. NWWNCAVL 4:26 PM EDT on June 19, 2008
Why does the NHC have an Alt floater titled Fengshen showing the Yucatan Penn?


Cause that broad area around 17N -93W caught my eye this afternoon (see my post below)....Lol; I wish..........Probababy just a temporary error on the part of both NHC and Me....Lol
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166. all4hurricanes
8:33 PM GMT on June 19, 2008
wow cat 3
I think Its really hard for a cyclone to develop in the west pacific and not become a Cat 4
while your on the way to becoming a cat 4 why don't you just skip several of the not so important stops like typhoon and major typhoon
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165. hurricanehanna
8:32 PM GMT on June 19, 2008
Floodman, did you say Manila? My hubby is there for another week and a half. And he was worried about leaving Louisina in case we got a hurricane here. Wonder what their warning system is like.
Does Cantore travel that far? Just pickin'
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164. NWWNCAVL
8:25 PM GMT on June 19, 2008
Why does the NHC have an Alt floater titled Fengshen showing the Yucatan Penn?
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163. Stormchaser2007
8:20 PM GMT on June 19, 2008
07WFENGSHEN.65kts-974mb-107N-1276E.100p



Little too close for comfort.

Its Pretty much done with eye formation

Member Since: June 9, 2007 Posts: 4 Comments: 15921
162. weathermanwannabe
4:13 PM EDT on June 19, 2008
Do any of the models show any possibilities for the area around Bay of Campeche/Yucatan in the near future?.................Thanks (No Rush)....
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161. HadesGodWyvern (Mod)
7:39 PM GMT on June 19, 2008
here is what PAGASA said earlier....
-----------

Tropical Storm "FRANK" is expected to enhance the southwest monsoon and bring rains over the rest of Mindanao and Visayas and later to Southern Luzon. 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 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 a.m. tomorrow.

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160. Stormchaser2007
7:42 PM GMT on June 19, 2008
157. 159. ROFLMAO.....ill see gotta get 24 of em!
Member Since: June 9, 2007 Posts: 4 Comments: 15921
159. pearlandaggie
7:38 PM GMT on June 19, 2008
154. i hope their CFLs! LOL
Member Since: September 14, 2007 Posts: 3 Comments: 3963
158. Drakoen
7:37 PM GMT on June 19, 2008
The CMC, NOGAPS, and ECMWF models bring Fengshun on land. The UKMET model has it extremely close to land while the GFS keeps it a little further east than the UKMET. Most likely the system will come very close to land if not make landfall.
Member Since: October 28, 2006 Posts: 57 Comments: 30562
157. TampaSpin
3:38 PM EDT on June 19, 2008
154. Stormchaser2007 3:36 PM EDT on June 19, 2008
Yeah gotta go pick some light bulbs up at the hard ware store....be back later.


Make sure you get the enviromentally good ones.........LMAO....
Member Since: September 2, 2007 Posts: 178 Comments: 20443
156. Nolehead
7:33 PM GMT on June 19, 2008
atmoaggie, that's so true...our company went over to biloxi & gulfport and did everything we could do to help out...neighbors helping each other...the way it should be..
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155. Floodman
2:34 PM CDT on June 19, 2008
151. atmoaggie

Yep, I lived in Mandeville for a number of years...through the lovely Katrina's arrival...it's a wonder that there are any businesses left south of the Interstate; they jumped their rates by 300-600 percent after the storm, if you could them to write at all... and trust me, Citizens is no option!
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154. Stormchaser2007
7:35 PM GMT on June 19, 2008
Yeah gotta go pick some light bulbs up at the hard ware store....be back later.
Member Since: June 9, 2007 Posts: 4 Comments: 15921

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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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