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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504. 69Viking
10:21 AM CDT on June 20, 2008
499. TampaSpin

So your sprinkler system is hooked up to city water and not tapped into a well? If you're tapped into a well they can't say anything because you're just recycling ground water.
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503. Patrap
10:21 AM CDT on June 20, 2008
I just link folks their 5 day forecast.Link

Everything is available there.
Im sure the Manila Folks are up on the warnings..
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502. melwerle
3:20 PM GMT on June 20, 2008
Morning Flood!
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501. 69Viking
10:17 AM CDT on June 20, 2008
470. TampaSpin

If my memory is right you have to upload the new photo and select a check box on the upload page that makes it your portrait.
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499. TampaSpin
11:17 AM EDT on June 20, 2008
493. 69Viking 11:16 AM EDT on June 20, 2008
450. TampaSpin

Wouldn't a sprinkler system tapped into a well be cheaper than re-sodding your lawn?


Got a sprinkler system .....water restrictions are very high....and Tampa has fined over 450 people in the last 30 days....$150 first offense $450 second time.....wow
Member Since: September 2, 2007 Posts: 178 Comments: 20439
498. Floodman
10:17 AM CDT on June 20, 2008
489. Patrap

Well truth be told, Pat, I told her that the environment would have to meet a lot of requirements for this thing to hit in the area of Manila, so I hedged quite a bit; nevertheless I told her it was pretty unlikely...based on the conditions at the time
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497. RasBongo
3:12 PM GMT on June 20, 2008
463

I am no expert on that call.

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496. tornadofan
3:15 PM GMT on June 20, 2008
Post 479 - I just got a Wx watch for my bday

Congrats! Is it a Severe T-storm watch, Tornado watch, of a Flash Flood watch?
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495. Floodman
10:15 AM CDT on June 20, 2008
Another reason I'll never be rich:

Good Mornin' Judge

Can you tell I'm on a 10cc binge this morning?
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494. Drakoen
3:15 PM GMT on June 20, 2008
Good morning everyone! I see that Fengshen has made it well west into the Phillipines as that mid to upper level ridge over China has stayed persistent allowing for a more west ward propagation than forecasted. A 500mb shortwave trough moving over Japan will erode the eastern portion of the ridge allowing for the system to make that turn to the NW and N.
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493. 69Viking
9:54 AM CDT on June 20, 2008
450. TampaSpin

Wouldn't a sprinkler system tapped into a well be cheaper than re-sodding your lawn?
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492. grayingwindsurfer
2:45 PM GMT on June 20, 2008
Dr. Masters,
Thank you for the excellent discussion on flooding. Unlike meteorology, I know something about this topic and have 2 comments.
1)There will NOT be an increase in 100 year floods, but there will LIKELY be an increase in the magnitude of the 100 year flood. This is semantics--The 100 year flood is merely the statistically predicted once-in-a-hundred-years flood (1% chance each year).
2)Chris Milly of the USGS/NOAA GFDL (Geophysical Fluid Dynamics Lab) has done much of the work used by the IPCC to estimate & summarize effects of climate change on where stream runoff will increase and decrease. In a recent article he and his coauthors make the point that "Stationarity is Dead". I'm not sure stationarity is a word, but the point is that the traditional method of using past data to predict the 100-year flood will not work because the climate is changing. Northern latitudes are predicted to have more runoff and, as you point out, increased number and magnitude of the severe events that produce flooding.
Milly, et.al. 2008, Stationarity is Dead: Whither Water Management? Science V. 319, 1 Feb. 2008, p. 573-574
Milly, et.al. 2005, Global pattern of trends in streamflow and water availability in a changing climate. Nature V. 438 no. 17 p. 347-350
Milly, et.al. 2002, Increasing Risk of Great Floods in a Changing Climate. Nature V. 415 p. 514-517
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491. Skyepony (Mod)
3:13 PM GMT on June 20, 2008
Tampa~ click my photos on the left, then upload a portrait. The last one you upload should automatically be your primary portrait. Or just upload one in the next few minutes. I'll try & catch it & make it your avatar..
Member Since: August 10, 2005 Posts: 161 Comments: 37424
490. Floodman
10:13 AM CDT on June 20, 2008
I know you were, Tampa...you know what, jp, I DO care about folks...that's why I'll never be rich...LOL
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489. Patrap
10:14 AM CDT on June 20, 2008
Forecasting is for the Pros,the NWS and the other official agencies...

Were all Hobbyists if your not a Degreed Met.


Always rely and use the Local official Statements for your area.
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488. TampaSpin
11:14 AM EDT on June 20, 2008
Well said JP
Member Since: September 2, 2007 Posts: 178 Comments: 20439
487. weathermanwannabe
11:06 AM EDT on June 20, 2008
Good Morning Folks......Quiet out in the tropical atlantic this am and I took next week off from work so I'm a happy camper this Friday morning....(except for the crushing heat later today in North Florida and the Flood victims in the US....Make sure you make it a point to provide some financial contributions to the Red Cross, etc., this week if you can for those Folks).....
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486. TampaSpin
11:13 AM EDT on June 20, 2008
484. Floodman 11:12 AM EDT on June 20, 2008

I was just kidding you know that.....
Member Since: September 2, 2007 Posts: 178 Comments: 20439
484. Floodman
10:10 AM CDT on June 20, 2008
Nope...I'll let them stand...I only said that because the trof looked like it would pick it WEST of the islands
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483. IKE
10:08 AM CDT on June 20, 2008
469. jphurricane2006 9:56 AM CDT on June 20, 2008
how is the shear over and ahead of the East Atlantic wave?


I'd say under 20 knots.
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482. TampaSpin
11:09 AM EDT on June 20, 2008
478. Floodman 11:07 AM EDT on June 20, 2008
I should learn to keep my mouth shut...looks like Fengshen IS going to hit Manila; the latest track from post 453 (thanks, all4) has it running right through Luzon and over the top of Manila...I told some nice lady in here yesterday that it didn't appear that it would...


Flood go back and edit your comments...
Member Since: September 2, 2007 Posts: 178 Comments: 20439
481. Skyepony (Mod)
3:07 PM GMT on June 20, 2008
NJ: Man survives lightning strike to head

one not so lucky

Windstorm kills pilot on layover

Midwest flood latest news

& from NOAA


more NOAA info here


& to liven things up today NOAA released this.. Scientific Assessment Captures Effects of a Changing Climate on Extreme Weather Events in North America

credit NOAA
Member Since: August 10, 2005 Posts: 161 Comments: 37424
480. Patrap
10:07 AM CDT on June 20, 2008
Philippines Wunderground locations Link
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479. FLWeatherFreak91
11:03 AM EDT on June 20, 2008
I have a technical question for you guys... I just got a Wx watch for my bday yesterday and it has an altimeter that is giving me the MOST trouble. You can either calibrate it by

sea level pressure,

zero (like if you were at the beach) or,

a known altitude.

But no matter what I do- it ends up being wrong... google earth has my house as being 58 ft above sea level. So I input that as the known value, but when I went to the beach yesterday the altimeter read 25 ft. I just can't seem to figure it out so if someone knows anything about this, can you help please?
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478. Floodman
10:05 AM CDT on June 20, 2008
I should learn to keep my mouth shut...looks like Fengshen IS going to hit Manila; the latest track from post 453 (thanks, all4) has it running right through Luzon and over the top of Manila...I told some nice lady in here yesterday that it didn't appear that it would...
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477. DDR
3:05 PM GMT on June 20, 2008
.
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476. Floodman
10:04 AM CDT on June 20, 2008
Good morning folks...figured I'd start the day with a little music:

Art for Art's Sake
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475. TampaSpin
11:04 AM EDT on June 20, 2008
473. melwerle 11:01 AM EDT on June 20, 2008
alrighty then...if someone ever figures out how to do that, let me know. I've got about 10 of the same pictures in my album now...just a little bit nuts...

Ok...back to the weather.


dido......lol
Member Since: September 2, 2007 Posts: 178 Comments: 20439
474. Patrap
10:01 AM CDT on June 20, 2008
To change your avatar,just click on the Avatar here,and use the "Modify This Image" button down the page,upload new pic and check the "Primary Portrait for Bio" box.
Easy
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473. melwerle
3:00 PM GMT on June 20, 2008
alrighty then...if someone ever figures out how to do that, let me know. I've got about 10 of the same pictures in my album now...just a little bit nuts...

Ok...back to the weather.

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472. CJ5
2:59 PM GMT on June 20, 2008
I too am impressed with the EATL wave right now it would be very impressive in Aug/Sept and would be the talk of the town. Lets see how it does this early..
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471. Patrap
9:56 AM CDT on June 20, 2008
Atlantic Ocean View (Updated ~3 hours)
GOES-12
3 Channels IR,WV and Low Cloud Vis Link
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470. TampaSpin
10:55 AM EDT on June 20, 2008
464. Weather456 10:51 AM EDT on June 20, 2008
try uploading and setting it as ur primary photo


456 already tried that....it does not work.

Member Since: September 2, 2007 Posts: 178 Comments: 20439
468. thelmores
2:51 PM GMT on June 20, 2008
the new wave in the e. atlantic may be far enough north to be a player.....
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467. Patrap
9:52 AM CDT on June 20, 2008
Tropical Basin Loop, GOES-12 WV (CH-3) with Dry Air Shaded Link
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466. tropicfreak
10:51 AM EDT on June 20, 2008
Well soon jamacia should.
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465. melwerle
2:50 PM GMT on June 20, 2008
ok Tampa - thought it was just me...my kids couldn't even figure it out so I figure that my age isn't inhibiting me...(16 year olds can fix a tv faster than anyone my age)

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464. Weather456
2:49 PM GMT on June 20, 2008
try uploading and setting it as ur primary photo
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463. MasterForecaster
2:43 PM GMT on June 20, 2008
Ras you think this thing has a legit shot? Invest today?
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462. RasBongo
2:48 PM GMT on June 20, 2008
460

Jamaica is dry for now
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461. TampaSpin
10:48 AM EDT on June 20, 2008
459. melwerle 10:46 AM EDT on June 20, 2008
Ok - so stupid question of the day - how do you change your avatar photo...


Mel i have been trying to do that for days....lol good luck i hope someone knows.
Member Since: September 2, 2007 Posts: 178 Comments: 20439
460. tropicfreak
10:45 AM EDT on June 20, 2008
Looks like the lessler antillies barbados and jamacia are getting heavy downpours.
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459. melwerle
2:46 PM GMT on June 20, 2008
Ok - so stupid question of the day - how do you change your avatar photo...

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458. bimshire
10:44 AM EDT on June 20, 2008
I have had 1.10 inches of rain for the day here in Barbados.

Was quite looking forward to going to cricket to see the Aussies play the West Indies in a 20/20 match but judging by the amount of cloud still to pass it is looking a bit dodgy. Will still keep my fingers crossed.
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457. Tazmanian
7:40 AM PDT on June 20, 2008
Tropicaldiscussion has a nic update he all so talks about the next pulse of the MJO and he talks about what is a MJO and the Effect of the MJO on cyclonic development


Link
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456. RasBongo
2:38 PM GMT on June 20, 2008
And the ITCZ has a lot of fuel to make it grow
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455. melwerle
2:38 PM GMT on June 20, 2008
Morning JP - I'll wave at them...

Had an INCREDIBLY storm pop up from no where here yesterday. Was in the movie theatre (btw - don't bother wtih the new adam sandler movie) and kept getting texts asking if I was someplace safe. Hail, tornado warnings, HEAVY rain and lightning...would love another one like that today please...my lawn is MUCH happier.
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454. RasBongo
2:36 PM GMT on June 20, 2008
451

The amazing part is that it starts to rotate so far in the EATL
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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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