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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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: September 2, 2007 Posts: 178 Comments: 20439
1503. cchsweatherman
8:03 PM EDT on June 22, 2008
GFS forecasts favorable shear in the GOM in about 18 hours. Lets see if this spin can hold until then.
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1502. thelmores
12:02 AM GMT on June 23, 2008
Tampa, if you keep saying something will develop, it eventually will! LOL

You have proven that, for about the last 5 days! :D

It is common for multiple "swirls" to develop along an existing trough..... still not quite ready to buy any tropical development in the Gulf with this mess.....

there is a decent pressure drop there though......

too bad we will soon loose visible.....

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1501. cchsweatherman
7:57 PM EDT on June 22, 2008
Damn! Nice catch Tampa. I will be watching this area with great interest. It will be very interesting to see the next QuikSCAT image. If anything, its moving towards the ENE, not NNE. But, as usual, persistence is key.
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1500. sporteguy03
11:59 PM GMT on June 22, 2008
From the 8:05 TWD:
Gulf of Mexico...
shortwave upper trough extends over the wrn Gulf with axis
extending from ern Texas along 95w to near 21n. An upper-level
ridge extends from the Caribbean over the ern Gulf into the far
W Atlc over the NW Bahamas. This is supplying most of the Gulf
with WSW upper flow. Scattered showers and tstms continue E of
the trough axis along a surface trough which extends from Mobile
Alabama to near 27n93w...continuing as a secondary surface
trough in the Bay of Campeche.

There is nothing there.
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1499. TampaSpin
7:56 PM EDT on June 22, 2008
1498. Stormchaser2007 7:56 PM EDT on June 22, 2008

Pretty wild huh.....i think that has a chance to develop....but it is in shear of about 30kts..
Member Since: September 2, 2007 Posts: 178 Comments: 20439
1498. Stormchaser2007
11:49 PM GMT on June 22, 2008
1495. Thanks Alot now im gonna be addicted to that area all night!!...lol seriously.... theres defiantly a Mid level to Low level Circ there! thanks for the loop! Im gonna be waching this closely....
Member Since: June 9, 2007 Posts: 4 Comments: 15776
1497. InTheCone
7:43 PM EDT on June 22, 2008
1487 - Thanks Tampa!!

I'm packing up and heading out, may as well beat the evac. rush - lol!!

Seriously, I have a feeling you may just be right on the money.
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1496. TampaSpin
7:49 PM EDT on June 22, 2008
Gang we have a LLC developing in the BOC at 21N 94.5W.....Get ready it is moving NNE.
Member Since: September 2, 2007 Posts: 178 Comments: 20439
1495. TampaSpin
7:46 PM EDT on June 22, 2008
Pull up this link NASA loop it 20 times.....put the mouse on the BOC area...and speed it up very fast .....it will blow your mind away.....wow
Member Since: September 2, 2007 Posts: 178 Comments: 20439
1494. Stormchaser2007
11:44 PM GMT on June 22, 2008
1491. Yeah agree with ya completely...its gonna be interesting to watch!
Member Since: June 9, 2007 Posts: 4 Comments: 15776
1493. Stormchaser2007
11:44 PM GMT on June 22, 2008
1492. yeah...sure!
Member Since: June 9, 2007 Posts: 4 Comments: 15776
1492. TampaSpin
7:42 PM EDT on June 22, 2008
Stormchaser wanta see something cool.
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1491. TampaSpin
7:39 PM EDT on June 22, 2008
1490. Stormchaser2007 7:37 PM EDT on June 22, 2008
TS look at your image...look in the BOC and there appears to be some kinda circulation there!


Exactly there are about 2 very good spins in that area currently.....hard to tell which one will take off but, the begin of something i think is occurring......
Member Since: September 2, 2007 Posts: 178 Comments: 20439
1490. Stormchaser2007
11:35 PM GMT on June 22, 2008
TS look at your image...look in the BOC and there appears to be some kinda circulation there!
Member Since: June 9, 2007 Posts: 4 Comments: 15776
1489. TampaSpin
7:30 PM EDT on June 22, 2008
The potential is getting higher that something will develop in this area of the GOM. It is under Shear of 10-20Kts. Things cannot keep bubbling in that area long without something developing......

Member Since: September 2, 2007 Posts: 178 Comments: 20439
1488. atmoaggie
11:18 PM GMT on June 22, 2008
Couple answers to that, too.

From a conversation with a NDBC instrumentation QC engineer: The wave heights can be measured to about 50 feet reliably on their deep-water buoys...after that the tether to the mooring point will break free. I asked her this after some 30 foot waves during Dean last year.

BUT, the sensor sampling FAQ says 35 meters...Link

Also of interest here might be that, depending on the sensor package, or payload, any wind speed over 62 m/s usually cannot be accurately measured. (That would be 120 knots)
Member Since: August 16, 2007 Posts: 6 Comments: 12461
1487. TampaSpin
7:07 PM EDT on June 22, 2008
Gang as a mere weather buff at best, things are setting up in the tropics that do not appear favorable for the Con. US. The big as_ high in the Azores is as strong as i have ever seen this time of year......SST's are on the rise and starting to run above average in most locations where development occurs. Models are showing below average shear is forcasted...things better change or storms will be lining up like a freight train coming into North America and Central America. Be prepared for the start of JULY. Just my opinion!
Member Since: September 2, 2007 Posts: 178 Comments: 20439
1486. pearlandaggie
11:16 PM GMT on June 22, 2008
ahhhh, very cool. i wonder how much extra length they add to the mooring line to account for fluctuations in wave height.
Member Since: September 14, 2007 Posts: 3 Comments: 3963
1485. atmoaggie
11:14 PM GMT on June 22, 2008
The satellite uplink doesn't cost much if you already own the satellite and it was paid for to do many other things also...GOES.
Member Since: August 16, 2007 Posts: 6 Comments: 12461
1484. pearlandaggie
11:11 PM GMT on June 22, 2008
thanks, atmo. i was beginning to wonder if i was ever going to get a response. i guess that satellite uplink can be pretty costly!

i didn't know there was such a thing as an AWOL buoy!

thanks again, buddy!
Member Since: September 14, 2007 Posts: 3 Comments: 3963
1483. atmoaggie
11:08 PM GMT on June 22, 2008
pearlandag,

The NDBC buoys all transmit obs by satellite.
Link

Another note, look at buoy 44004...has drifted about since March, I think. Some 800 miles, or so, from it's moored location, but still transmitting good obs (along with it's current location, thankfully).

Also, the link says every hour, but we get obs from some buoys every 15 minutes.
Member Since: August 16, 2007 Posts: 6 Comments: 12461
1482. pearlandaggie
11:06 PM GMT on June 22, 2008
the temp in Pearland today was 97F with a relative humidity of 11%!!! I don't think it gets that dry in the winter!
Member Since: September 14, 2007 Posts: 3 Comments: 3963
1481. txalwaysprepared
10:26 PM GMT on June 22, 2008
Oh yeah. Wow look at all that dry air over me :(
Looks like I will be turning the hose on tomorrow.
Member Since: August 18, 2007 Posts: 0 Comments: 1642
1480. TampaSpin
6:14 PM EDT on June 22, 2008
1478. txalwaysprepared 6:11 PM EDT on June 22, 2008

Nearly the entire Eastern seaboard of the CON US has a trough in place that areas of low pressure spin off creating storms. You can see from this water vapor pic.

Member Since: September 2, 2007 Posts: 178 Comments: 20439
1478. txalwaysprepared
10:10 PM GMT on June 22, 2008
1476. That's what I was saying.. all storms are going to FL. I'd like some rain here, but it doesn't look like that will happen.

I can't help you with the intensity question. Sorry.

TS - are the showers following the front that came through here yesterday?
Member Since: August 18, 2007 Posts: 0 Comments: 1642
1477. txalwaysprepared
10:09 PM GMT on June 22, 2008
probably... with my demonic baby pic :)
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1476. 7544
10:05 PM GMT on June 22, 2008
another round of heavy storms in se fla forming also that blob just east of texas is that moving east also to give another round as they cross the state from west to east they get sronger ?
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1475. TampaSpin
6:03 PM EDT on June 22, 2008
1474. txalwaysprepared 6:01 PM EDT on June 22, 2008

Your not scaring everyone away are ya.....lol
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1474. txalwaysprepared
10:01 PM GMT on June 22, 2008
just a dead blob ;)

Florida isn't sharing the rain
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1473. TampaSpin
5:52 PM EDT on June 22, 2008
Just logged in anything happening in the GOM since this morning
Member Since: September 2, 2007 Posts: 178 Comments: 20439
1472. txalwaysprepared
9:53 PM GMT on June 22, 2008
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1471. Weather456
5:31 PM AST on June 22, 2008
Something similar to this in 2008 expected:

Member Since: July 24, 2005 Posts: 407 Comments: 19076
1470. Weather456
5:21 PM AST on June 22, 2008
Now, I'm sure a stronger storm could potentially break through a weaker ridge. I'm not sure what other factors (besides Coriolis) would lead to such an event.

It would also be easier for a astrong frontal trough to break down the high causing more recurvature for storms in the Caribbean. Remember Ivan. Bonnie and Charley.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1469. Drakoen
9:21 PM GMT on June 22, 2008
Here's the MSLP for the days that Francis was alive you'll notice that the 1016 isobar was to the north as the weak Azores and Bermuda high were of the north allowing Francis to take a more WNW path. The ridge axis from the high extended outward towards Florida.

Member Since: October 28, 2006 Posts: 57 Comments: 29886
1468. BahaHurican
4:50 PM EDT on June 22, 2008
Thanks for the feedback, Drak. This confirms my thinking that it's not simply the location of the high, or even how strong it is in terms of pressure (e.g. 1031 mb) but also the shape / extent of the high that influences storm direction.

Now, I'm sure a stronger storm could potentially break through a weaker ridge. I'm not sure what other factors (besides Coriolis) would lead to such an event.
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1467. Drakoen
9:07 PM GMT on June 22, 2008
1466. txalwaysprepared 9:06 PM GMT on June 22, 2008
1465. West where? Like SA and CA?


GOM and CA in 2007.
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1466. txalwaysprepared
9:05 PM GMT on June 22, 2008
1465. West where? Like SA and CA?
Member Since: August 18, 2007 Posts: 0 Comments: 1642
1465. Drakoen
8:48 PM GMT on June 22, 2008
1463. msphar 8:47 PM GMT on June 22, 2008
What I notice from those charts is that the High pressure forms a ridge extending West towards the islands South of Florida, I guess forming a wall to guide the storm towards the West.


Yep. Nice big wall protecting us. From what I have been seeing we may not be as lucky this year especially if we get a negative NAO during the heart of the season which the dynamical models are showing below average pressure readings this year in the mid-Atlantic.
Member Since: October 28, 2006 Posts: 57 Comments: 29886
1464. txalwaysprepared
8:44 PM GMT on June 22, 2008
I know nothing about the buoys. I know nothing about much of this stuff.. that's why I am here, so the resident experts can guide me along.

But I do know that an 11 month old that is only 21 inches tall.. something is wrong there. I'm thinking you meant 21 lbs. (?) But I do hope she is found quickly!

Still wanting rain from that blob :)
Member Since: August 18, 2007 Posts: 0 Comments: 1642
1463. msphar
8:38 PM GMT on June 22, 2008
What I notice from those charts is that the High pressure forms a ridge extending West towards the islands South of Florida, I guess forming a wall to guide the storm towards the West.
Member Since: August 20, 2006 Posts: 0 Comments: 289
1462. Drakoen
8:37 PM GMT on June 22, 2008
Here's MLSP for the mean days Felix was alive. You'll notice how far south the 1015mb isobar was which was responsible for Felix's low latitude.
Member Since: October 28, 2006 Posts: 57 Comments: 29886
1461. pearlandaggie
8:37 PM GMT on June 22, 2008
great question Baha, and great response Drak!
Member Since: September 14, 2007 Posts: 3 Comments: 3963
1460. pearlandaggie
8:33 PM GMT on June 22, 2008
i just thought of something i had never really pondered before...i guess oceanic buoys have a satellite uplink for data transfer, right? the buoys have solar cells to produce power for the instruments, so it only follows that the remote data acquisition must involve a satellite uplink. is this correct? does anyone know?
Member Since: September 14, 2007 Posts: 3 Comments: 3963
1459. Drakoen
8:33 PM GMT on June 22, 2008
1456. BahaHurican 8:28 PM GMT on June 22, 2008
Am I right in thinking that where the 1016 isobar is, there the hurricane shall be also?


For the most part depending on the strength of the hurricane. Here's the mean position of the high for the days that Dean was alive. You'll notice how far south the 1015mb isobar was:

Member Since: October 28, 2006 Posts: 57 Comments: 29886
1458. severstorm
4:31 PM EDT on June 22, 2008
anyone near port st lucie fl your now under a tornado warning
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1457. washingaway
3:27 PM CDT on June 22, 2008
Hi all, Just checked the buoys, buoy 42055 in the BOC has SW winds and falling pressure, Buoy 42002 east of Brownsville has NW winds and falling pressure. Any thoughts?
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1456. BahaHurican
4:24 PM EDT on June 22, 2008
Am I right in thinking that where the 1016 isobar is, there the hurricane shall be also?

I've been trying to find archived graphics (i.e. surface maps) for last year. I'd like to look at the maps while Dean / Felix were in the Caribbean to see just how far south that high extended.
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1455. pearlandaggie
8:27 PM GMT on June 22, 2008
Fengshen not nearly as impressive as earlier, either...

Member Since: September 14, 2007 Posts: 3 Comments: 3963
1454. msphar
8:21 PM GMT on June 22, 2008
Drak, Thanks. I understand the implication leading on from there. Will continue to watch the Tropical Surface Analysis. The H looks good for now, but I notice they move around from time to time.
Member Since: August 20, 2006 Posts: 0 Comments: 289

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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.