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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1604. weatherblog
5:16 AM GMT on June 23, 2008
Space, were do you get your Data from? How So? You realize its only June and we already have had Arthur? Do you have any Charts and Graphs to indicate a Slow Season? Do you know that it only takes one? If your going to consider tranquill seasons, that would place 1992 under that.. With Hurricane Andrew. On this blog its best not to say opinions on the whole season without Data and info. If you do, I'd gladly love to see it.

Agree completely.
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1603. CybrTeddy
5:10 AM GMT on June 23, 2008
1567. SpaceThrilla1207 3:22 AM GMT on June 23, 2008 Hide this comment.
I agree with JP, nothing will form out of our BOC low and this will be a more tranquil year than expected...In my opinion this will be a 2006 type year.

Oh, and STORMTOP shut up...that post was totally un called for.


Space, were do you get your Data from? How So? You realize its only June and we already have had Arthur? Do you have any Charts and Graphs to indicate a Slow Season? Do you know that it only takes one? If your going to consider tranquill seasons, that would place 1992 under that.. With Hurricane Andrew. On this blog its best not to say opinions on the whole season without Data and info. If you do, I'd gladly love to see it.
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1602. weatherblog
4:57 AM GMT on June 23, 2008
1601. PanhandleChuck 4:54 AM GMT on June 23, 2008
If another Dennis, I hope it doesen't follow the same track. It was small, but it tore this town apart


Well, that was the 2005 season, and all bets were off during that season. In just July, typically a quiet month, they had two long tracked major hurricanes. And, yeah, Dennis was a bad hurricane damage wise. Similar to Wilma which also did incredible damage where I live.
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1601. PanhandleChuck
11:52 PM CDT on June 22, 2008
If another Dennis, I hope it doesen't follow the same track. It was small, but it tore this town apart
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1600. weatherblog
4:52 AM GMT on June 23, 2008
Nothing in the tropics. Not suprised really, but by the end of June, I still expect 1-2 more named storms... One storm in the CATL; one in the Caribbean/GOM. I know it sounds crazy, but this has been my prediction from the beginning, and I'm sticking with it.

For July, I expect 2-3 named storms... I also wouldn't be suprised to see some Dennis/Emily/Bertha scenarios either...
Just my opinion.
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1599. PanhandleChuck
11:47 PM CDT on June 22, 2008
Americans are xenophobics? Maybe that could explain why a nation with so much educational resourses, only 10 percent of their population or less speak only one language. While in the rest of the world the percent is much higher with less resourses. In Cuba for example a country that they critizice so much, 75 percent or more of the population speak two or more languages.

HurakanPR - I have no need to speak more than 1 language. I can understand everybody that I need to
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1598. HurakanPR
12:37 AM AST on June 23, 2008
Americans are xenophobics? Maybe that could explain why a nation with so much educational resourses, only 10 percent of their population or less speak only one language. While in the rest of the world the percent is much higher with less resourses. In Cuba for example a country that they critizice so much, 75 percent or more of the population speak two or more languages.
1597. hahaguy
12:43 AM EDT on June 23, 2008
ya i'm here lol
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1596. PanhandleChuck
11:36 PM CDT on June 22, 2008
Is there anybody out there?
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1595. PanhandleChuck
11:29 PM CDT on June 22, 2008
Good evening / morning all... been working all weekend, anything of interest???????
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1594. moonlightcowboy
11:18 PM CDT on June 22, 2008
I'm out, gang! Have a good sleep, Pottery, Drak and all.
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1593. moonlightcowboy
11:15 PM CDT on June 22, 2008
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1592. moonlightcowboy
11:15 PM CDT on June 22, 2008
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1591. moonlightcowboy
11:13 PM CDT on June 22, 2008
Tranquil? I don't think so.
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1590. Drakoen
4:10 AM GMT on June 23, 2008
The CFS isn't that excited about El Nino breaking out with .5 being the highest it goes keeping it within the neutral range. This months dynamical and statistical models are largely in favor of ENSO neutral conditions.
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1589. moonlightcowboy
11:04 PM CDT on June 22, 2008
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1588. Drakoen
3:57 AM GMT on June 23, 2008
1587. moonlightcowboy 3:57 AM GMT on June 23, 2008
1585. Look again, Drakoen. I updated it, sorry!


Yea that looks better.
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1587. moonlightcowboy
10:57 PM CDT on June 22, 2008
1585. Look again, Drakoen. I updated it, sorry! We're near neutral conditions, now.
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1586. pottery
11:51 PM AST on June 22, 2008
Some decent convection building to the south/east of me, off Guyana.
Also, a flare up in the Trop. Atl right now looking good. At about 10n 40w
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1585. Drakoen
3:53 AM GMT on June 23, 2008
I don't think that meter is accurate MLC...
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1584. BahaHurican
11:54 PM EDT on June 22, 2008
Same 2 u, MLC.
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1583. moonlightcowboy
10:53 PM CDT on June 22, 2008
Have a good sleep, cchs and Baha! A GR8 week, too!
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1582. BahaHurican
11:45 PM EDT on June 22, 2008
Good night, all!
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1581. cchsweatherman
11:49 PM EDT on June 22, 2008
Good night all! Unless something develops, I will not be here for a couple days. I will be focusing on getting everything on my website updated since it has not been updated for quite some time. If anyone has any questions or comments for me, just message me. I will check my messages.
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1580. moonlightcowboy
10:48 PM CDT on June 22, 2008


...from NOAA Watch.
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1579. moonlightcowboy
10:42 PM CDT on June 22, 2008
The tropics are seldom tranquil or quiet. Just
pick any year and you'll see storms that
formed, even dangerous ones in years that
didn't produce many storms.

Just because a storm doesn't hit the CONUS,
doesn't make a tranquil season. Ask the folks
in Nicaragua last year, they'll say it wasn't
tranquil.

But, there's no evidence that leans towards a
slower season either. Conditions are and
forecast to be favorable with two or three
meteorological entities predicting an above
active season.

It only takes one to destroy life and property.
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1578. pottery
11:44 PM AST on June 22, 2008
LOL Houston. But the cloud image did not show. Just a blue questionmark. Am I alone in this ?
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1577. BahaHurican
11:44 PM EDT on June 22, 2008
Houst,

I saw an x rather than a cloud.
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1576. pottery
11:41 PM AST on June 22, 2008
Its an Inquiring Cloud I think.

These clouds stick to the sky
Like a floating question why,
They linger there to die,
They dont know where ther're going
And my friend neither do I.........

Paul Simon



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1574. BahaHurican
11:38 PM EDT on June 22, 2008
1571. Drakoen 11:34 PM EDT on June 22, 2008

We already started. We just haven't continued.


Agreed. I was thinking more about active part of season.
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1573. pottery
11:39 PM AST on June 22, 2008
Its an Inquiring Cloud I think.
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1571. Drakoen
3:33 AM GMT on June 23, 2008
1570. BahaHurican 3:33 AM GMT on June 23, 2008
Actually, given the fact that we are coming out of a la nina into a neutral phase of ENSO, it's more likely we'll have a LATE start rather than an early one . . .


We already started. We just haven't continued.
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1570. BahaHurican
11:31 PM EDT on June 22, 2008
Actually, given the fact that we are coming out of a la nina into a neutral phase of ENSO, it's more likely we'll have a LATE start rather than an early one . . .
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1569. pottery
11:30 PM AST on June 22, 2008
I hear you Thrilla.
I dont believe you though........
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1568. Drakoen
3:26 AM GMT on June 23, 2008
Where's the evidence that supports this year will be "tranquil"?

2004's first storm didn't form until July 31st and 2005's second storm didn't form until June 28th.
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1567. SpaceThrilla1207
3:21 AM GMT on June 23, 2008
I agree with JP, nothing will form out of our BOC low and this will be a more tranquil year than expected...In my opinion this will be a 2006 type year.

Oh, and STORMTOP shut up...that post was totally un called for.
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1564. HurricaneKing
10:59 PM EDT on June 22, 2008
NorthxCakalaky,
Didn't your name used to not have the x or am I crazy?
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1563. pottery
10:53 PM AST on June 22, 2008
NorthX That sounds pretty dread
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1562. NorthxCakalaky
2:44 AM GMT on June 23, 2008
06/22/2008 0130 PM

2 miles E of Galax, Carroll County.

Hail e0.88 inch, reported by public.


Hail 4 to 6 inches deep in some areas.





06/22/2008 0134 PM

10 miles E of Hillsville, Carroll County.

Hail e0.75 inch, reported by trained spotter.






06/22/2008 0125 PM

Galax, City of Galax County.

Hail e0.88 inch, reported by trained spotter.


Hail covering the ground.





06/22/2008 1250 PM

Byllesby, Carroll County.

Hail e0.88 inch, reported by trained spotter.


I live 2counties away from V.A. Glad I didnt see 6inches cover the ground.I have been to Galax which is about 3counties away from here.

Flash flood warnings were issued from the mountains of N.C to the coast.(individaul counties)Wilmington,N.C reported knee deep water in city locations.Lots of areas reported hail and flooding.

I emailed the N.C Severe Weather Expert about a picture I had of what looked like a funnel.He told me it looked like a shelf cloud or a scud.

More Severe weather 4 Monday is expected.
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1561. pottery
10:41 PM AST on June 22, 2008
Greetings. It all looks very quiet and civilised here tonight.
Blobs in the GOM. Blobs in the Atl.
But nothing threatening apparently.
Forecast for the southern Islands calling for rains and strong squalls from tomorrow through Wednesday.
Well bring it on I say.
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1560. presslord
2:18 AM GMT on June 23, 2008
Drak...I appreciate your response to my request for rain in the Lowcountry...but...ah...you can stop now...gettin a bit soggy....
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1559. txalwaysprepared
2:06 AM GMT on June 23, 2008
OK FL, I know yall need the rain.. but so do we. Can we all share? ;)
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1558. XoendHoroeken
9:57 PM EDT on June 22, 2008
So, it does appear (according to the NWS forecast discussion) that Tampa and the surrounding West Coast of Fl may be awakened early tomorrow morning by yet another round of thunderstorms. This could potentially add another 1-1.5" on top of the FIVE that I have received in the past week.
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1557. Drakoen
1:46 AM GMT on June 23, 2008
I'm not expecting any development for at least another week. Conditions remain unfavorable for tropical cyclone development. A persistent tropical upper tropospheric trough with the axis extending down into the eastern Caribbean has spawned a big upper level low north of the Lesser Antilles. A shortwave trough lies in the eastern Gulf of Mexico. Strong upper level winds have prevailed with these features with subsidence over the Central Caribbean.

The GFS shows an upper level high coming into to play in the Caribbean a week from now which may allow for something to form as the upward motion of the MJO moves into the region as shown by the EWP and GFS. Still none of the long range computer models predict tropical cyclone formation in the Caribbean at that time frame.
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1556. BahaHurican
9:32 PM EDT on June 22, 2008
I really think that mid-July is the first period where there is a serious formation threat. That's the point when everything is likely to come together - SSTs, MJO, ITCZ, low shear, high location vs. SAL coverage - so far we haven't really had all these ingredients in sync.
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1554. stormdude77
9:20 PM AST on June 22, 2008
If accuweather is right, it could be very windy around my area on Tuesday. Forecast for my area below:

Tuesday, Jun 24 Winds gusting past 80 kph in the morning; humid with intervals of clouds and sunshine. Winds from the NE at 45 km/h.
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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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