Two 500-year floods in 15 years

By: Dr. Jeff Masters , 2:48 PM GMT on June 19, 2008

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.

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.

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

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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1054. MississippiWx
4:35 PM CDT on June 21, 2008
JP...Look at the marine discussion on the current Houston forecast discussion.
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1053. tiggeriffic
9:33 PM GMT on June 21, 2008
hey there Moon! How goes it today?
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1052. Stormchaser2007
9:32 PM GMT on June 21, 2008
1050.Yeah gonna go and check the NAM....
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1051. Weather456
5:25 PM AST on June 21, 2008
Its amazing how almost everything I remembered from Dennis and Emily were masked by Katrina, Rita and Wilma. Its also amazing how the low pressure by Katrina, was masked by Rita, which was masked by Wilma. The places who werent affected by a single storm in 2005, like the NE Caribbean, were very very lucky that lucky that year.
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1048. StormHype
9:12 PM GMT on June 21, 2008
Hey, do you any of you guys remember this Wilma related Youtube video?
Nope, cause I was tagging with a pro chaser on a media contract and we were all over Marco Island and Naples from sunday night through monday when it came ashore. We rode out 20 minutes of 130mph winds in a 2 level parking ramp on Marco Island when the eye wall came over us. It was in the middle of the night, but I'll never forget that sound and experience. Luckily I got quite a bit on video in case I want to relive it when my alzheimers sets in about 50 years from now.
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1047. msphar
9:00 PM GMT on June 21, 2008
Yes Levi I was speaking of the continent of SA
and all that land mass implies including the shear that sets up on it blows East or North from it. That stuff and the desiccated air from the african desert all tend to gang up on the waves after they emerge. Its like a gauntlet, or as I like to think of it a gigantic bowling alley with the windards in the frontal pin location. Gutter balls go toward Trinidad or Puerto Rico. Current wave will be of the former but lets see if it can climb. The HIGH to the North is currently holding it South chances are that pressure will continue to have an effect.
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1045. txalwaysprepared
9:05 PM GMT on June 21, 2008
NVM I found it. Gotta love this site. If I would just look it's all right here :)
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1044. txalwaysprepared
9:01 PM GMT on June 21, 2008
Can someone tell me where to find a good map online to print out to track these "blobs"

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1043. IKE
4:00 PM CDT on June 21, 2008
That's about as big of a wave as I've seen in the Atlantic so far this season...looks like it's got a high over it.......


Terrible shear north.......
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1042. Weather456
4:56 PM AST on June 21, 2008
Another impressive tropical wave and blow up along the ITCZ with a barber shop to its north, but amazing how quickly dry air tends to dissipate.

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1041. Weather456
4:48 PM AST on June 21, 2008
In addition, one of the characteristics of Frank's Inverted V tropical wave model developed for mainly for tropical waves between the Cape verdes and the Lesser Antilles was that, tropical waves were hindered from amplifying northwards due to the dry enviroment to there north, but once they enter the more moist, warm and unstable area of 50W, they amplify their true strength northwards and affect the islands.

If you look back in the TWD archive or have a good memory, you'll see the NHC mentioned the amplification of the wave was hindered by SAL to its north in its early life cycle.
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1040. moonlightcowboy
3:52 PM CDT on June 21, 2008
Convection building out at 9n,35w.
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1039. Levi32
12:50 PM AKDT on June 21, 2008
Thanks I totally screwed up on the reply to what someone said about SA......I thought he meant the Saharan dust layer lol.
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1038. moonlightcowboy
3:46 PM CDT on June 21, 2008
1037. I'm so glad you've pointed that out 456. Huge misconception exists there. Good point! Thanks.
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1037. Weather456
4:39 PM AST on June 21, 2008
Some were saying the previous wave was SA bound. But what happen to waves that pull north out of the ITCZ like the last two ones. The problem is...we are looking a steering map that steers tropical cyclones which are at the surface (1013 mb to 943 mb). Tropical waves are embedded within the 500-850 mb easterlies. Two totally different steering levels.

The last wave was south of 10N when it was east of 40W. Then south of 21N west of 60W, which is a WNW/NW direction, yet the surface flow was westerly and even southwesterly at times. The wave had to be steered by something else or atleast embedded within a different single layer.
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1036. Levi32
12:27 PM AKDT on June 21, 2008

Well there have been many years where the high has been set up like this, but it isn't that abnormal. As we get into the latter part of July and August we'll start to see waves further north developing in the central and eastern Atlantic.
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1035. pearlandaggie
8:24 PM GMT on June 21, 2008
has there ever been a ABH setup that consistently sent tropical waves into South America?
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1034. Levi32
12:20 PM AKDT on June 21, 2008
1033. msphar 12:17 PM AKDT on June 21, 2008
Levi I see the wave but that large piece of SA may have adverse impact on its continued track.

There isn't that much dry air/SA north of the wave. And the dry air/SA in and of itself does not affect the track of tropical waves. What is steering this is the Bermuda high to its north, which will keep it on a west or WNW track. The high is bringing a little bit of SA off of Africa and sending it west, but not much right now.
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1033. msphar
8:11 PM GMT on June 21, 2008
Levi I see the wave but that large piece of SA may have adverse impact on its continued track.
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1032. WeatherRhino
8:17 PM GMT on June 21, 2008

Those are great pictures. We have had some ugly clouds in the past hour.
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1031. Levi32
12:16 PM AKDT on June 21, 2008
1028. pearlandaggie 12:12 PM AKDT on June 21, 2008 Hide this comment.
JFV...i'm NOT a professional in this field! LOL...just putting in my 2 cents :)

Lol same here
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1029. WeatherRhino
8:11 PM GMT on June 21, 2008
Yup, the porto potty adds a classy touch. :o) Our beach got hit bad during Jean and Frances. They are starting a beach renovation July 1st. Thats why the portos are there. :o) I can make the picture large.
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1028. pearlandaggie
8:11 PM GMT on June 21, 2008
JFV...i'm NOT a professional in this field! LOL...just putting in my 2 cents :)
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1026. Levi32
12:06 PM AKDT on June 21, 2008
JFV -- That's a healthy-looking tropical wave embedded in the ITCZ. It might have a chance at developing if it can work its way north and become independent of the ITCZ during the next few days as it tracks west.
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1025. FLWeatherFreak91
4:06 PM EDT on June 21, 2008
I took these pics from Westchase, Fl earlier today as the Storms were approaching. I later recieved .75" hail and 39 mph wind. I've had 1.8" of rain so far, and it's still comin'.

img src="Photobucket" alt="" />pic 1
img src="Photobucket" alt="" />

img src="Photobucket" alt="" />pic3

img src="Photobucket" alt="" />
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1024. msphar
7:59 PM GMT on June 21, 2008
JFV - Looks to me like the ITCZ is getting restless. It needs to climalogically speaking. Jun 24th is just around the corner. Thats the center point for its historical northerly shift day.
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1023. pearlandaggie
8:01 PM GMT on June 21, 2008
1019. do you have a larger version?
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1022. HurrikanEB
7:48 PM GMT on June 21, 2008
Happy Summer/Winter (depending on your hemisphere) everyone

(i know that im a day late)
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1021. pearlandaggie
7:59 PM GMT on June 21, 2008
1019. WOWWWWWWWW! that's an AMAZING picture! i love the colors! (save the port-o-lets in the foreground!) LOL
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1020. pearlandaggie
7:58 PM GMT on June 21, 2008
JFV, looks like a big, messy, disorganized blob! LOL how's that? :)
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1019. WeatherRhino
7:59 PM GMT on June 21, 2008
This is a storm that is moving across the ocean in Vero Beach FL. I took this about 10 minutes ago.
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1017. msphar
7:53 PM GMT on June 21, 2008
Undoubtedly on the double edge effect. Deep stuff on the CRF, it would take a while to digest those papers. But now I must switch gears towards the Tropics. Getting the sunscreen ready for a short immersion.
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1015. pearlandaggie
7:46 PM GMT on June 21, 2008
1014. cooling is a double-edged sword. while it is nice for skiing and the like, it means shorter, cooler growing seasons and more energy expended for heating.
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1014. msphar
7:40 PM GMT on June 21, 2008
The butterfly chart is very revealing. Some much of this stuff ties together well. Looking forward to some cooling. Should be good for skiing over the remainder of my life.
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1013. pearlandaggie
7:39 PM GMT on June 21, 2008
msphar, here's some other stuff, if you're interested...



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1012. pearlandaggie
7:38 PM GMT on June 21, 2008
you're most welcome! there's a lot of stuff out there if you just know where to look!!
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1011. msphar
7:28 PM GMT on June 21, 2008
Just wanted to say "THANKS" to PEARLANDAGGIE for directing me to the fascinating info revolving around sunspot study available online. It opened a lot of windows for me.
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1009. Levi32
11:03 AM AKDT on June 21, 2008
1005. cchsweatherman 10:57 AM AKDT on June 21, 2008 Hide this comment.
For Levi and Kman - Go to the NASA satellite page, select animate for the visible imagery, and zoom into the area. You will clearly see low-level circulation.

Yeah I see it....mid-level not low-level. It's not very strong at all if the vorticity maps are accurate. Oh well....this wave will more than likely follow its predecessors into Central America without any development.
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1008. kmanislander
7:03 PM GMT on June 21, 2008
gotta run an errand. back later
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1007. kmanislander
6:57 PM GMT on June 21, 2008

Low level turning does not necessarily mean a surface low. T Waves carry a wind shift along their axis which causes the turning and is the signature of a wave. We see wind shifts depicted all the time on quikscat.

In answer to CyberTeddy, the presence of the anit-cyclone overhead accounts for the lack of shear in that area. That is what gives it the chance for development but it would need to lift a few degrees further North to benefit from the coriolis effect as well as to avoid South America
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1006. Levi32
11:02 AM AKDT on June 21, 2008
1003. Skyepony 10:43 AM AKDT on June 21, 2008 Hide this comment.
By that latest pass looks like it's gonna stay well east of Manila, avoiding the land. Best scenario for them consider where it was.

Levi~ did that look donut before it hit that bigger island or what?

I gotta shut down. Here comes a severe thunderstorm.

It wasn't quite donut. What happened was northern side was being eroded by dry air (still is right now) so all the outer bands were almost non-existent on that side, making it look like a donut after the EWRC was complete. That was really impressive to watch though. Stay safe Skye!

CATL wave to continue west with the steering currents under the big high for the next few days. I'd like to see this get further north and more independent from the ITCZ before development can occur.

Free image hosting

^Click to enlarge^

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1005. cchsweatherman
2:55 PM EDT on June 21, 2008
For Levi and Kman - Go to the NASA satellite page, select animate for the visible imagery, and zoom into the area. You will clearly see low-level circulation.
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1004. spayandneuter
2:28 PM EDT on June 21, 2008
Glad to see some chatter here about evacuating with pets. Horses, cattle and other large animals are even more difficult. If you have horses and they are not used to being loaded into a trailer, start the lessons now! It will make your life easier. In the California fires we had so many horses that had never been trailered and we ended up having to lead them out for miles to a safe place.

Remember that a disaster can be anything, not just a hurricane, flood or tornado. Fires (house fire is #1), chemical spills and even terrorism should be concerns. What happens if there is a huge chemical spill that blocks the highway leading to your home? What would you do? tough questions that we all need to think about. You can organize your neighbors to help each other in the event you are not home. You can either join or create your own CERT (citizens emergency response team) in your area. Your state's Agriculture department or SART (state agriculture response team) can help you with this. Many times SERT's and SART's are the first responders on the scene and can mean life and death for your animals.

If someone can tell me how to do it, I will post a "one page family disaster plan" which is an excellent format to help you get organized with all your information and your animals' information as well.

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Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather

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