Two 500-year floods in 15 years

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

Share this Blog
1
+

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

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 1554 - 1504

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34Blog Index

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.
Member Since: Posts: Comments:
1553. thelmores
1:19 AM GMT on June 23, 2008
pressures seems to have leveled off..... if they go down from here..... IR certainly doesn't look too impressive.......

Member Since: Posts: Comments:
1552. thelmores
1:13 AM GMT on June 23, 2008
1550

what.... the NAM???
Member Since: Posts: Comments:
1551. hahaguy
9:09 PM EDT on June 22, 2008
Agreed thelmores
Member Since: Posts: Comments:
1549. thelmores
1:06 AM GMT on June 23, 2008
well, I'm out too..... see if I can get a little fraggin done before bed time.....

I do this we have conjured up a "glimpse" of the coming season today..... with the azores high, increased temps, and lower than average shear..... sounds like a bad combination to me.....
Member Since: Posts: Comments:
1548. moonlightcowboy
8:02 PM CDT on June 22, 2008
1544. Thanks, stormdude! So, all is relatively quiet in the tropics! Aaaahh, the quiet before the storms. But, whoa, when Neptune releases his fury, soon! UGH!
Member Since: July 9, 2006 Posts: 184 Comments: 29610
1547. thelmores
1:04 AM GMT on June 23, 2008
night surfmom....
Member Since: Posts: Comments:
1545. surfmom
12:55 AM GMT on June 23, 2008
Wish I could stay up late and play...but up b/4 the roosters tomorrow.
Got rained out of work on Saturday, so I have quite a bit of catch up in the barn, with all the rain "fungus amongus" will be the theme --keeping SWFL horses free of it is a full time job, but it's better then them dealing with heat stress when there is not rain.

Happy to say that seeding was done on Friday & the rain goddess heard my prayers - trying out Argentine Bahia - (per the boss) it will be interesting to see how well it does.

Take care all and perhaps we will have a spinner to look at tomorrow!
Member Since: Posts: Comments:
1544. stormdude77
8:55 PM AST on June 22, 2008
MLC...nothing worth mentioning in the CATL at this time, that's ITCZ convection around 8-10N, 30-35W. There's a Twave around 45W, but strong wind shear is affecting it
Member Since: Posts: Comments:
1543. thelmores
12:57 AM GMT on June 23, 2008
agreed JP.... in the "soup" we have in the gulf, not uncommon to have a swirl or two....

and you know better than watching the NAM for genesis! LOL lucky guess by the NAM! :D

what caused the small anticyclone over Barry last year.... was it just pure chance? and if the shear relaxes as some have indicated, could it happen again?

possible I guess, but chances are pretty low.... right??
Member Since: Posts: Comments:
1542. surfmom
12:52 AM GMT on June 23, 2008
1518 - yes cchs GREAT shots
Member Since: Posts: Comments:
1540. thelmores
12:53 AM GMT on June 23, 2008
what did they "call Barry?"
Member Since: Posts: Comments:
1539. surfmom
12:51 AM GMT on June 23, 2008
not to be rude, but there were a handful of surfers that called Barry
Member Since: Posts: Comments:
1538. thelmores
12:46 AM GMT on June 23, 2008
JP..... are you ever wrong? LOL

seriously, I agree with your observations, I just like giving you crap! LOL

NOBODY...... myself included, saw Barry coming.... sort of like the current situation.....

but thats why we ae here right? I mean if it was an absolute science, where would the fun be! ;)
Member Since: Posts: Comments:
1537. moonlightcowboy
7:50 PM CDT on June 22, 2008
Stormdude, what's that out at 8-10n, 30-33w? Anything happening way out there?
Member Since: July 9, 2006 Posts: 184 Comments: 29610
1536. stormdude77
8:39 PM AST on June 22, 2008
1527. moonlightcowboy 8:39 PM AST on June 22, 2008

LOL...
Member Since: Posts: Comments:
1535. moonlightcowboy
7:44 PM CDT on June 22, 2008
Catch a bunch, TS! Man, that sure sounds good! Enjoy!
Member Since: July 9, 2006 Posts: 184 Comments: 29610
1533. thelmores
12:44 AM GMT on June 23, 2008
have a good one Tampa..... catch some big fish, and get some pics for us! :)
Member Since: Posts: Comments:
1532. moonlightcowboy
7:42 PM CDT on June 22, 2008
Hey, TS! Glad you're eyeballing everything. Someone has to keep a faithful watch for a sneeker. It's coming soon enough!



No vorticity to speak of, up until the 500mb level and up.
Member Since: July 9, 2006 Posts: 184 Comments: 29610
1531. thelmores
12:41 AM GMT on June 23, 2008
Whatever it is, it is heading straight for buoy 42055... be interesting to see the next couple observations.
Member Since: Posts: Comments:
1530. Dakster
12:43 AM GMT on June 23, 2008
MLC,

LMAO... I thought told you not to feed the trolls...
Member Since: Posts: Comments:
1529. TampaSpin
8:40 PM EDT on June 22, 2008
Gotta go for now...gotta 2 hour drive to brothers house....going fishing......lol
Member Since: Posts: Comments:
1528. thelmores
12:39 AM GMT on June 23, 2008
More like a Cat .5! LOL
Member Since: Posts: Comments:
1527. moonlightcowboy
7:37 PM CDT on June 22, 2008
What? Cat 5 headed to NOLA? OMG! ;P
Member Since: July 9, 2006 Posts: 184 Comments: 29610
1526. thelmores
12:38 AM GMT on June 23, 2008
could be some remains of Karen as well! LOL
Member Since: Posts: Comments:
1525. TampaSpin
8:36 PM EDT on June 22, 2008
1516. thelmores 8:23 PM EDT on June 22, 2008

You are correct......DMax will be very interesting....every Satel. update is showing a better appearance.
Member Since: Posts: Comments:
1524. BahaHurican
8:29 PM EDT on June 22, 2008
Well, the Gulf is one of two favored areas for development at this time of year. I'm not seriously expecting any development from this, but if SOMEthing's going to pop, I suppose it could do so there.

Seems like "ghost of Alma-Arthur" if it did . . .
Member Since: Posts: Comments:
1523. thelmores
12:30 AM GMT on June 23, 2008
JP..... TS Barry from last year......

Posted by: JeffMasters "The hurricane season of 2007 officially began today, and we officially have our second surprising named storm of the season--Tropical Storm Barry. Barry is highly unusual in that it developed in the presence of strong wind shear--about 20-40 knots. I've never seen a tropical storm form under more than about 25 knots of wind shear."

So it can happen....... still not likely though!
Member Since: Posts: Comments:
1522. cchsweatherman
8:26 PM EDT on June 22, 2008
Showing favorable shear within 12 hours.

Member Since: Posts: Comments:
1521. STORMTTOP
12:25 AM GMT on June 23, 2008
Great destruction and devastation will befall the coastlines soon.
Member Since: Posts: Comments:
1520. thelmores
12:25 AM GMT on June 23, 2008
ok Tampa..... sorry if I offended you, just trying to have a little fun....
Member Since: Posts: Comments:
1519. thelmores
12:23 AM GMT on June 23, 2008
jp, don't you remember a storm last year in a similar location "did" for a TS.....

Likely? no..... possible? Certainly!
Member Since: Posts: Comments:
1518. cchsweatherman
8:20 PM EDT on June 22, 2008
Some great shots. It even shows on the IR imagery. Both images are courtesy of Penn States Satellite page.

Member Since: Posts: Comments:
1517. TampaSpin
8:20 PM EDT on June 22, 2008
1513. thelmores 8:19 PM EDT on June 22, 2008

I have only pointed out areas that had the potential for develpment......i stated at the end of this trough as one........i also pointed out the Low pressure that has been consistent near South America in the SW Carribean.......not wishcasting just stating observations...that is not wishcasting when stating observations.
Member Since: Posts: Comments:
1516. thelmores
12:23 AM GMT on June 23, 2008
Tampa, right again..... Dmax may get interesting! LOL

Member Since: Posts: Comments:
1514. TampaSpin
8:18 PM EDT on June 22, 2008
I don't think it is completely to the surface yet......but it could get there.
Member Since: Posts: Comments:
1513. thelmores
12:17 AM GMT on June 23, 2008
oh come on Tampa, don't make me go back into the blog and quote you for the last 3-4 days! LOL

Lighten up friend, no offense meant! ;)
Member Since: Posts: Comments:
1512. TampaSpin
8:15 PM EDT on June 22, 2008
if you do an infared loop you can see it is starting to wrap some convection.
Member Since: Posts: Comments:
1511. thelmores
12:15 AM GMT on June 23, 2008
updated buoy plot.........



pressures high, winds low...... guess we'll see if anything comes about in this area.... the shear seems to be the inhibiting factor, but if cchs is right..... who knows.... stranger things have happened!
Member Since: Posts: Comments:
1510. TampaSpin
8:14 PM EDT on June 22, 2008
1509. thelmores 8:13 PM EDT on June 22, 2008
And they say wishcasting doesn't work! LOL

Tampa has proved em wrong! :D


Wishcasting......???
Member Since: Posts: Comments:
1509. thelmores
12:12 AM GMT on June 23, 2008
And they say wishcasting doesn't work! LOL

Tampa has proved em wrong! :D
Member Since: Posts: Comments:
1508. TampaSpin
8:13 PM EDT on June 22, 2008
LMAO,,,,
Member Since: Posts: Comments:
1507. Stormchaser2007
12:06 AM GMT on June 23, 2008
Im calling it Tampas Low!!

Member Since: June 9, 2007 Posts: 4 Comments: 15921
1506. thelmores
12:08 AM GMT on June 23, 2008
1504...

LOL....
Member Since: Posts: Comments:
1505. thelmores
12:08 AM GMT on June 23, 2008
TS Tampa! LOL

Member Since: Posts: Comments:
1504. TampaSpin
8:03 PM EDT on June 22, 2008
Thanks CCHS i was going fishing tomorro in the GOM, but i just changed plans.......lol
Member Since: Posts: Comments:

Viewing: 1554 - 1504

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34Blog Index

Top of Page

About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

Local Weather

Overcast
66 °F
Overcast