Two 500-year floods in 15 years

By: Dr. Jeff Masters , 02:48 PM GMT on Juni 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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354. BahaHurican
8:29 AM EDT on June 20, 2008
Morning again. Most recent forecast track of Fengshen/Frank takes it just east of Manila, but keeps it at Cat 1. This could be a bad situation for the Philippines, since this storm looks like a gullywasher. Can u say flooding, landslides etc?

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353. stormdude77
8:30 AM AST on June 20, 2008
Morning everyone

Nice flare up of convection this morning around the islands...

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351. Weather456
8:23 AM AST on June 20, 2008
349. jphurricane2006 8:23 AM AST on June 20, 2008

For the first time since tracking this tropical wave (ECARIB), the Western Caribbean maybe favorable enough for development in 96 hrs-120 hrs. The wave is moving very quickly off towards the west, and in 72 hrs it should be near Jamaica, which should give it a slight window of opportunity before moving into central America. I give a slight chance of development in the WCARIB.

As for the second wave, very impressive on the SAL Maps. Dust is rather to its north but also ahead to its NW but thinner than the first wave but still evident on visible imagery. QuikSCAT showed a highly amplified wave supporting 25 knot winds. The steering flow continues to be pretty strong south of the subtropical ridge. I mean, the first wave took 5 days to reach the islands compared to 7 days for a normal wave. This is hindering the waves from developing an decent LLCC despite their impressiveness. Along with surface-500 mb RH humidity percentage in the 30s and wind shear, I expect little of this wave over the next 72 hrs.
Member Since: Juli 24, 2005 Posts: 407 Comments: 19076
348. Weather456
8:15 AM AST on June 20, 2008
As at 1200 UTC

CANEFIELD, Dominica - light rain shower
COOLIDGE, Antiqua - moderate thunder shower
LE, Guadeloupe - overcast skies
Member Since: Juli 24, 2005 Posts: 407 Comments: 19076
347. Weather456
8:09 AM AST on June 20, 2008
Very heavy downpour and gusty winds just reached St. Kitts right on time....Friday Morning.
Member Since: Juli 24, 2005 Posts: 407 Comments: 19076
346. Weather456
8:00 AM AST on June 20, 2008
Trp Wave lighten up the radar this morning



Trp wave in EATL displaying an impressive structure (QuikSCAT)

Member Since: Juli 24, 2005 Posts: 407 Comments: 19076
345. IKE
6:27 AM CDT on June 20, 2008
That eastern Caribbean wave is a survivor....

Dedicated to it..........

His best song
Member Since: Juni 9, 2005 Posts: 23 Comments: 37858
344. guygee
10:48 AM GMT on June 20, 2008
Re:338. aspectre 7:54 AM GMT on June 20, 2008

It is important to realize that it is FEMA and not the USGS or USACE or anyone else that has ultimate control in the determination of flood recurrence intervals and corresponding flood plains. The relevant law is U.S Code Title 42, Ch.50, National Flood Insurance. In particular see TITLE 42, Ch.50, SUBCHAPTER III, section 4101. Identification of flood-prone areas.

FEMA alone has the power to "consult with, receive information from, and enter into any agreements or other arrangements with the Secretaries of the Army, the Interior, Agriculture, and Commerce, the Tennessee Valley Authority, and the heads of other Federal departments or agencies, on a reimbursement basis, or with the head of any State or local agency, or enter into contracts with any persons or private firms" as they see fit to make the determination.

After the maps are made, it is another matter to certify where a specific property fits in the FEMA flood zone map. This matter seems to be entirely in the private sector, mostly for the purpose of determining the need for obtaining required flood insurance prior to obtaining a secured loan or mortgage. For example, by following a legal case in Iowa, I found one such private firm that is in the business of making flood zone determinations, which broadly speaking involves providing the certified location of property in relation to a FEMA flood zone map: First American Flood Data Services. I am sure there are many other such firms.
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342. HadesGodWyvern (Mod)
9:51 AM GMT on June 20, 2008
Philippines Atmospheric Geophysical Astronomical Services Administration

Typhoon "FRANK" has made landfall over Eastern Samar and is now heading towards Bicol region.

Tropical Cyclone Bulletin #8
============================
At 5:00 P.M. PST, Typhoon Frank located near 11.5°N, 125.1°E or in the vicinity of Western Samar and 50 kms Southeast of Catbalogan City has sustained winds of 75 knots with gusts up to 90 knots.

Storm Signals Raised
====================

Warning Signal #3 (100-185 km/h)

Luzon Region
1.Camarines Norte
2.Camarines Sur
3.Albay
4.Burias Island
5.Sorsogon
6.Catanduanes
7.Masbate

Visayas Region
1.Samar Provinces
2.Leyte
3.Biliran Island

Mindanao Region
1.No Signal Raised

Warning Signal #2 (60-100 km/h)

Luzon Region
1.Quezon
2.Polillo Island
3.Marinduque
4.Romblon

Visayas Region
1.Northern Cebu
2.Southern Leyte

Mindanao Region
1. No Signals Raised

Warning Signal #1 (30-50 km/h)

Luzon Region
1.Aurora
2.Rizal
3.Laguna
4.Batangas
5.Cavite
6.Mindoro Provinces
7.Metro Manila

Visayas Region
1.Antique
2.Aklan
3.Capiz
4.Iloilo
5.Rest of Cebu
6.Bohol
7.Siquijor Island
8.Negros Provinces
9.Guimaras

Mindanao Region
1.Dinagat
2.Siargao Island

Public Storm Signals #1 elsewhere is now lowered.

Typhoon "FRANK" is expected to enhance the southwest monsoon and bring rains over Southern Luzon, rest of Visayas and Mindanao. Residents in low lying areas and near mountain slopes are advised to take all the necessary precautions against possible flashfloods and landslides.

Likewise, those living in coastal areas under signal 2 and 3 are alerted against big waves or storm surges generated by this tropical cyclone.

The public and the disaster coordinating councils concerned are advised to take appropriate action and watch for the next bulletin to be issued at 11 p.m. today.
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341. 7544
8:45 AM GMT on June 20, 2008
nice blowup on our island wave at 5 am
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340. BahaHurican
4:41 AM EDT on June 20, 2008
I'm going back to bed.
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339. BahaHurican
4:36 AM EDT on June 20, 2008
It seems Fengshen is going further west than originally expected. Navy website is posting forecast strengthening to 105 kts in the next 48 hours.

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338. aspectre
7:46 AM GMT on June 20, 2008
Homes and businesses flooded after FEMA assures lenders and borrowers that flood insurance isn't needed.
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337. HadesGodWyvern (Mod)
7:28 AM GMT on June 20, 2008
Japan Meteorological Agency

WWJP25 Weather Chart Synopsis (0000z 20Jun)
=============================================

LOW PRESSURE AREA (96W)
20.0ÂșN 149.0ÂșE - 15 knots 1008 Hpa

Reported moving west-northwest at 10 knots

-----------

System #3

Japan Meteorological Agency

No Current Bulletins Or Advisories for this system

Joint Typhoon Warning Center

Tropical Disturbance Summary (0600z 20Jun)
===========================================

An area of convection (97W) located near 21.1N 175.1E or 490 NM east-northeast of Wake Island. Recent animated multispectral satellite imagery shows convection developing along the periphery of an elongated low level circulation center evident in a 1804z Quikscat Pass. A mid to upper level low pressure area deepening to the surface over the past several days has spurred the development of this low leel circulation center. Sea surface temperatures in the area are high enough to support deep convection near the low level center, which could serve to both intensify the low level circulation and transition the vertically deep parent circulation into a warm core structure. However, upper level convergence into the low pressure area aloft will likely surpress development of this necessary deep convection for the next 24 hours.

Maximum sustained surface winds near the center is 17-22 knots with a minimum sea level pressure of 1007 mb. Because the disturbance is associated with a non-tropical feature and consequent upper level conditions are not likely to support rapid transition into a tropical system, the potential for this disturbance to form into a significant tropical cyclone within the next 24 hours is POOR.
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336. msphar
7:16 AM GMT on June 20, 2008
Virtual Buoy for 18.0Âș N / 65.5Âș W reports
E winds 14 - 21 Kts Friday with waves 4 - 6 ft out of the East. Nice sailing weather unless you want to go East.
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335. msphar
7:13 AM GMT on June 20, 2008
The ITCZ is back in the low position perhaps leading the next wave astray.
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334. msphar
7:06 AM GMT on June 20, 2008
The Virgins have not been hit by the wave tonight, and that seems like a good thing. Maybe tomorrow.
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333. JLPR
5:50 AM GMT on June 20, 2008
Well folks my hurricane season contest is still going =)
We are getting close to the deadline for the second part which is June 30, 10 days away!!
So come and join =) Pass by my blog and drop your predictions there =)

Lets get to 50 entries!! =D
Thanks to all of the ones that have already joined and to the ones that decide to join too =)
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332. JLPR
5:49 AM GMT on June 20, 2008
night Weather456 =)
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331. JLPR
5:48 AM GMT on June 20, 2008
lol I guess they would have said well it was 70% not 100% =) there was a 30% chance it wouldn't rain =D
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330. Weather456
1:40 AM AST on June 20, 2008
329. JLPR 1:37 AM AST on June 20, 2008
=) good

the plants in the backyard are screaming RAIN! lol =P

but 30% lol thats not good =P I remembered I had a 70% last week and it was a very sunny day =D


lol....more like a 70% chance the forecast could be wrong.


Night all
Member Since: Juli 24, 2005 Posts: 407 Comments: 19076
329. JLPR
5:35 AM GMT on June 20, 2008
=) good

the plants in the backyard are screaming RAIN! lol =P

but 30% lol thats not good =P I remembered I had a 70% last week and it was a very sunny day =D
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328. Weather456
1:30 AM AST on June 20, 2008
327. JLPR 1:28 AM AST on June 20, 2008
Weather456 will Puerto Rico see showers from this Twave?


30% chance of showers from the bulk of the wave; which lies south of Puerto Rico, however, there are still the possibility that a few stray showers will pass along the northern edge of the wave.
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327. JLPR
5:26 AM GMT on June 20, 2008
Weather456 will Puerto Rico see showers from this Twave?
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326. smmcdavid
12:26 AM CDT on June 20, 2008
Bedtime for me... talk to you later.
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325. StormJunkie
5:25 AM GMT on June 20, 2008
Hope John is feeling better soon! My days haven't been quite that rough. Just busy.
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324. StormJunkie
5:22 AM GMT on June 20, 2008
322...Ohh, you were talking about you...I concur; been pretty busy myself !~)
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323. Weather456
1:17 AM AST on June 20, 2008
Twave bringing showers to the islands

Member Since: Juli 24, 2005 Posts: 407 Comments: 19076
322. smmcdavid
12:16 AM CDT on June 20, 2008
Hey SJ, been a rough couple of days... I should be around more in a day or two.
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321. StormJunkie
5:14 AM GMT on June 20, 2008
Evening smmc, good to see ya.

Thanks 456, wish that link had the mid level shear map.
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320. smmcdavid
12:11 AM CDT on June 20, 2008
Good evening... can't sleep. Anything exciting going on?
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319. Weather456
1:08 AM AST on June 20, 2008
Apply these analysis to the typhoon in the WPAC.
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318. StormJunkie
5:04 AM GMT on June 20, 2008
Thank you sir, excellent explanation!
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317. Weather456
12:57 AM AST on June 20, 2008
314. StormJunkie 12:53 AM AST on June 20, 2008
negative values - surface divergence

but upper divergence is a positive for convection correct?


yea it works the same way as surface convergence.

positive values - enhance upper outflow - air rises to place that outflow, and convection results.

negative values - enhance upper convergence - air has no way to go but downwards, suppress convection.

Upper divergence and surface convergence dont always work in perfect harmony with each other. One of the disruptive factors is mid-level dry air intrusion.

A tropical cyclone can fill if surface convergence is more than upper divergence, so that is something I look for signs of potential development or TC maintainence.
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316. StormJunkie
4:58 AM GMT on June 20, 2008
Thanks 456, that is what I thought.

Again, I just can not say enough about those CIMSS folks.
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315. Weather456
12:52 AM AST on June 20, 2008
313. StormJunkie 12:51 AM AST on June 20, 2008

mid-level shear - vertical wind shear between low levels and mid-levels

upper-level shear - vertical wind shear between low levels and upper levels.

For typical cyclogenesis, a storm can overcome 20 knots of shear but mid-level shear of 20 knots would be rather tough on that storm.
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314. StormJunkie
4:51 AM GMT on June 20, 2008
negative values - surface divergence

but upper divergence is a positive for convection correct?
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313. StormJunkie
4:46 AM GMT on June 20, 2008
309. I'm lost!

And here, mid shear, which I imagine needs to be under 15kts to really support development? It would be a little easier for a system to over come 20kts of shear in the upper levels?
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312. TampaSpin
12:48 AM EDT on June 20, 2008
310. StormJunkie 12:46 AM EDT on June 20, 2008

can't wait to hear this one.....lol
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311. Weather456
12:47 AM AST on June 20, 2008
SJ...correct

positive values - surface convergence - rising air - enhanced convection

negative values - surface divergence (negative function of convergence) - sinking air - suppressed convection.

Member Since: Juli 24, 2005 Posts: 407 Comments: 19076
310. StormJunkie
4:44 AM GMT on June 20, 2008
Hey me too TS!

Speaking of, learn me something 456.

This map


Positive values support convection correct?
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309. Weather456
12:44 AM AST on June 20, 2008
306. StormJunkie 12:42 AM AST on June 20, 2008
304. huh?


Oh... never mind

I just figured out why. I was using the number pad "plus sign key". You have to use the "shift = key"
Member Since: Juli 24, 2005 Posts: 407 Comments: 19076
308. Weather456
12:40 AM AST on June 20, 2008
That map shows current shear and shear trend in last 24hrs if I am not mistaken.

Correct...just a 24 hour trend.

Now it be good to have a map like that for atmospheric pressure but due to the inconsistency in reports across the Caribbean and Trp Atlantic, that would only be useful in the GOM, and SW North Atlantic.
Member Since: Juli 24, 2005 Posts: 407 Comments: 19076
307. TampaSpin
12:41 AM EDT on June 20, 2008
305. StormJunkie 12:40 AM EDT on June 20, 2008
More like an observation then a forecast


Yep thanks for straigten me out....i need all the help i can get..

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306. StormJunkie
4:40 AM GMT on June 20, 2008
304. huh?
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305. StormJunkie
4:36 AM GMT on June 20, 2008
More like an observation then a forecast.



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304. Weather456
12:37 AM AST on June 20, 2008
And if anyone is wondering the "plus sign" does show up on Wunder blogs. Wonder y?
Member Since: Juli 24, 2005 Posts: 407 Comments: 19076

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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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