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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1204. surfmom
4:23 AM GMT on June 22, 2008
Thanks Tigger , my best BUDDY is smart but he's a surfer soooo smart can be relative at timeS. most of the time he's at san juan,. but the wedding was scheduled to be in Cebu -- a very small village in the area of cebu
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1203. tiggeriffic
4:24 AM GMT on June 22, 2008
nite people, long day ahead tomorrow
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1202. Skyepony (Mod)
4:18 AM GMT on June 22, 2008
surfmom~ What part of the philippines? & I hear ya on the rain. Been very nice though I didn't ride, too much mud to groom off the pony.
Member Since: August 10, 2005 Posts: 156 Comments: 36074
1201. tiggeriffic
4:18 AM GMT on June 22, 2008
email is snail mail there surfmom, prob no power, all towers down or damaged, same thing in PR when Hugo hit, don't freak yet, give it a little time, you told him to prepare, trust he did...
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1200. surfmom
4:18 AM GMT on June 22, 2008
Tampaspin - i am in Sarasota FL
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1199. Skyepony (Mod)
4:10 AM GMT on June 22, 2008
Here's youtubes from Manila, the guy is talking in english about the Ferry rescue efforts while showing Fengshen.
Part 1
Part 2
Member Since: August 10, 2005 Posts: 156 Comments: 36074
1198. surfmom
4:12 AM GMT on June 22, 2008
sick w/worry re the hurricane in the Philippines, my best buddy,godfather of my surf son was to be married today -- he has not responded to my e-mails the past two days. Thanks to Hades I alerted him several days in advance that this storm would get ugly - I know he must be involved, but I am so worried
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1197. tiggeriffic
4:14 AM GMT on June 22, 2008
ok, bout time to go, gotta put new carpet in the boat tomorrow before the rain hits for the 3rd day in a row as well as putting all the seats back in...yuck!
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1196. Stormchaser2007
4:13 AM GMT on June 22, 2008
.
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1195. TampaSpin
12:13 AM EDT on June 22, 2008
Surfmom where do you live at in FL
Member Since: September 2, 2007 Posts: 177 Comments: 20430
1194. tiggeriffic
4:11 AM GMT on June 22, 2008
OMG, that would be like taking the Harbour Cruise in Charleston during Hugo or something... Duh people, boat, storm, sink, die??? Feel bad, don't get me wrong, but, dang it to all heck...
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1193. surfmom
4:04 AM GMT on June 22, 2008
so this is the late night crew , I am never awake at this time, but my older son - a commercial diver kept me up tonight, so here I am , the rain today in SWFL was a real blessing - it was so good to see the water hole out east at the polo club replenish. Too rainy to do much work w/the horses , and grateful for that
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1192. TampaSpin
12:09 AM EDT on June 22, 2008
1187. Skyepony 12:05 AM EDT on June 22, 2008

Sky not sure who made such an airless brainhead move to have a ferry in the middle of such a potent storm.......wow
Member Since: September 2, 2007 Posts: 177 Comments: 20430
1191. txalwaysprepared
4:07 AM GMT on June 22, 2008
TS... no not the smartest thing. I lost satellite and didn't have the computer on. But I knew they were tornado clouds. I was outside seeing where it may come from (and of course had a camera too lol). Kids had a grand time playing with daddy's guitar hero stuff they are usually not allowed to touch!! ;)
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1190. Skyepony (Mod)
4:08 AM GMT on June 22, 2008
It wouldn't be a 1st in the Philippines.
Member Since: August 10, 2005 Posts: 156 Comments: 36074
1189. tiggeriffic
4:07 AM GMT on June 22, 2008
do who, what? People were on a ferry during a hurrincane???? OMG
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1188. TampaSpin
12:02 AM EDT on June 22, 2008
1184. txalwaysprepared 11:58 PM EDT on June 21, 2008
TS LMAO.. not worried about it coming here. I had my fun today with a sudden tornado warning. Came out of nowhere. Had the kids in the closet while I took pics outside LOL


Don't know if that was wise to be outside taking pics.....but i can just see the kids in the closest going thru adults things hidden in closets.........LMAO

Member Since: September 2, 2007 Posts: 177 Comments: 20430
1187. Skyepony (Mod)
3:54 AM GMT on June 22, 2008
MANILA — Many of the 800 passengers and crew on a ferry that sunk off the Philippines are feared dead, the coast guard said Sunday.

The ferry sank in the aftermath of Typhoon Fengshen in the central Philippines, local officials said.

The typhoon also killed at least 18 people throughout the Philippines.
..more
Member Since: August 10, 2005 Posts: 156 Comments: 36074
1186. tiggeriffic
3:59 AM GMT on June 22, 2008
We had one last night, another storm today too, oldest son saw funnel dropping from sky right over where he works last night, watched the parked cars being pushed thru the parking lot...
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1185. Stormchaser2007
3:59 AM GMT on June 22, 2008
1184.ROFL!!
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1184. txalwaysprepared
3:57 AM GMT on June 22, 2008
TS LMAO.. not worried about it coming here. I had my fun today with a sudden tornado warning. Came out of nowhere. Had the kids in the closet while I took pics outside LOL
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1183. tiggeriffic
3:53 AM GMT on June 22, 2008
moving at a decent clip...
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1182. TampaSpin
11:54 PM EDT on June 21, 2008
I can't recall see so many CATl waves this strong this early......maybe i just have a bad memory......lol
Member Since: September 2, 2007 Posts: 177 Comments: 20430
1181. TampaSpin
11:49 PM EDT on June 21, 2008
1179. txalwaysprepared 11:45 PM EDT on June 21, 2008

it should reach Texas in 5 minutes......lol
Member Since: September 2, 2007 Posts: 177 Comments: 20430
1180. Stormchaser2007
3:45 AM GMT on June 22, 2008
Well see for your self
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1179. txalwaysprepared
3:43 AM GMT on June 22, 2008
How fast is the wave moving? Is it just me or does it seems to be booking it across the atl?
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1178. tiggeriffic
3:44 AM GMT on June 22, 2008
from the looks of it, could get a number soon...
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1177. Stormchaser2007
3:40 AM GMT on June 22, 2008
The Wave looks Pretty good right now...

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1176. Stormchaser2007
3:37 AM GMT on June 22, 2008
Shear wont be a problem if the anticyclone sticks around.

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1175. tiggeriffic
3:37 AM GMT on June 22, 2008
evening all, what's the scoop tonight (tropical wise) other than all the rain the south east has gotten over the past 2 days
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1174. THUNDERPR
3:29 AM GMT on Junio 22, 2008
I see the same is more organized and a bouy near 8 N 38 W (8°0'0" N 38°0'0" W)
report at 23:00 SW (220 deg)at 11.1 kts.
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1173. 0741
3:29 AM GMT on June 22, 2008
yes been watching this wave scince 5 am yrsterday and now it looks like it trying to develope this might get tagged 92l sometime on sunday imo what are u guys seeing
their too much shear for it to be 92l shear very high look what going on with wave in carribbean now
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1172. WeatherfanPR
3:32 AM GMT on June 22, 2008
good night JLPR
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1171. JLPR
3:29 AM GMT on June 22, 2008
before going =)
I do see some potential with this wave, maybe getting to invest status if it keeps its current convection and if it develops a low and if the anticlone it has over it right now moves west with the wave
As you can see there are a lot of ifs with this wave =P
now im leaving =)
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1170. WeatherfanPR
3:27 AM GMT on June 22, 2008
barbadosjulie, you can use the translator from thesaurus.com
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1169. THUNDERPR
3:23 AM GMT on Junio 22, 2008
bye JLPR
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1168. aspectre
3:24 AM GMT on June 22, 2008
130. barbadosjulie "...can anyone help with all of the Spanish..."

Babelfish does a good enough job for most things.
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1167. 7544
3:20 AM GMT on June 22, 2008
1159. THUNDERPR 3:04 AM GMT on June 22, 2008
THE GFS HAS BEEN FORECASTING 40-50 KT AEJ
WITH THIS LATTER WAVE AS IT MOVES ACROSS THE ATLC...AND AS THE
WAVE ENTERS THE LOCAL AREA AND MOVES MORE WNW...THE AEJ IS
FORECAST TO BE ACROSS THE LOCAL AREA. THIS TO OCCUR AS THE GFS
LIFTS TUTT AXIS IN TANDEM SLOWLY TO THE NW AS THE WAVE ENTERS THE
REGION...PUTTING THE WAVE IN AN AREA OF UPPER DIVERGENCE...AND
POTENTIALLY EXPLOSIVE ENVIRONMENT. GFS IS GOING QUITE AGGRESSIVE
WITH THIS NEXT WAVE AS IT ARRIVES INTO THE AREA SUNDAY NIGHT
THROUGH MONDAY...WITH VERY ACTIVE WEATHER AND VERY STRONG WINDS.
HAVE BEGUN TO NUDGE THE FORECAST IN THAT DIRECTION...AND WILL HAVE
TO WAIT AS IT EVOLVES.

yes been watching this wave scince 5 am yrsterday and now it looks like it trying to develope this might get tagged 92l sometime on sunday imo what are u guys seeing
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1166. WeatherfanPR
3:19 AM GMT on June 22, 2008
here is the most recent discussion from the National Weather Service in San Juan PR and it was at 2:12pm.

Discussion...
the latest sounding at tjsj shows much drier air in the middle- and
upper-levels of the atmosphere today with the passage of the
latest easterly wave. Latest aerosol optical thickness tools
indicate decent amounts of Saharan dust in the atmosphere today
creating hazy conditions for much of the local islands. This haze is
expected to drop off tomorrow in response to a middle-level TUTT
reflection upstream. The next African easterly wave should push
through the local islands by Monday morning. The latest GFS
guidance initializes properly with the wave position and both the
GFS and NAM stay on track with the Monday morning timing of the
event with speed maxes in the 700 mb wind fields...bringing
increased moisture in southeast flow. That being said...expect
increased shower and thunderstorm activity as well as the
possibility of gusty winds for Monday.


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1165. JLPR
3:22 AM GMT on June 22, 2008
well im out
till tomorrow everyone
good night =)
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1164. JLPR
3:15 AM GMT on June 22, 2008
THE LATEST GFS
GUIDANCE INITIALIZES PROPERLY WITH THE WAVE POSITION AND BOTH THE
GFS AND NAM STAY ON TRACK WITH THE MONDAY MORNING TIMING OF THE
EVENT WITH SPEED MAXES IN THE 700 MB WIND FIELDS...BRINGING
INCREASED MOISTURE IN SOUTHEAST FLOW. THAT BEING SAID...EXPECT
INCREASED SHOWER AND THUNDERSTORM ACTIVITY AS WELL AS THE
POSSIBILITY OF GUSTY WINDS FOR MONDAY.



Looks like some rain and winds Monday =)
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1163. THUNDERPR
3:11 AM GMT on Junio 22, 2008
its very far but this is the forecast discussion of the san juan weather office.
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1162. JLPR
3:12 AM GMT on June 22, 2008
oh my =O From where did you get that?
i need to start saving links =)
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1161. THUNDERPR
3:09 AM GMT on Junio 22, 2008
yes the wave in the central atlantic
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1160. 0741
3:05 AM GMT on June 22, 2008
THE GFS HAS BEEN FORECASTING 40-50 KT AEJ
WITH THIS LATTER WAVE AS IT MOVES ACROSS THE ATLC...AND AS THE
WAVE ENTERS THE LOCAL AREA AND MOVES MORE WNW...THE AEJ IS
FORECAST TO BE ACROSS THE LOCAL AREA. THIS TO OCCUR AS THE GFS
LIFTS TUTT AXIS IN TANDEM SLOWLY TO THE NW AS THE WAVE ENTERS THE
REGION...PUTTING THE WAVE IN AN AREA OF UPPER DIVERGENCE...AND
POTENTIALLY EXPLOSIVE ENVIRONMENT. GFS IS GOING QUITE AGGRESSIVE
WITH THIS NEXT WAVE AS IT ARRIVES INTO THE AREA SUNDAY NIGHT
THROUGH MONDAY...WITH VERY ACTIVE WEATHER AND VERY STRONG WINDS.
HAVE BEGUN TO NUDGE THE FORECAST IN THAT DIRECTION...AND WILL HAVE
TO WAIT AS IT EVOLVES.
((what wave??? the other way too far east of puerto rico.))
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1159. THUNDERPR
3:01 AM GMT on Junio 22, 2008
THE GFS HAS BEEN FORECASTING 40-50 KT AEJ
WITH THIS LATTER WAVE AS IT MOVES ACROSS THE ATLC...AND AS THE
WAVE ENTERS THE LOCAL AREA AND MOVES MORE WNW...THE AEJ IS
FORECAST TO BE ACROSS THE LOCAL AREA. THIS TO OCCUR AS THE GFS
LIFTS TUTT AXIS IN TANDEM SLOWLY TO THE NW AS THE WAVE ENTERS THE
REGION...PUTTING THE WAVE IN AN AREA OF UPPER DIVERGENCE...AND
POTENTIALLY EXPLOSIVE ENVIRONMENT. GFS IS GOING QUITE AGGRESSIVE
WITH THIS NEXT WAVE AS IT ARRIVES INTO THE AREA SUNDAY NIGHT
THROUGH MONDAY...WITH VERY ACTIVE WEATHER AND VERY STRONG WINDS.
HAVE BEGUN TO NUDGE THE FORECAST IN THAT DIRECTION...AND WILL HAVE
TO WAIT AS IT EVOLVES.
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1158. JLPR
3:01 AM GMT on June 22, 2008
wave =P
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1157. JLPR
2:59 AM GMT on June 22, 2008
though i didnt see the 45mph winds in the model it doesnt develop a Low with the tropical
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1156. moonlightcowboy
9:58 PM CDT on June 21, 2008
Whoa, Press! But, you're safe and have a backup plan. Cool.
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1155. THUNDERPR
2:54 AM GMT on Junio 22, 2008
if that winds 45 mph are correct in 48 hrs in puerto rico have winds near tropical storm forces in the surface , maybe this wave strenghtining near puerto rico.
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1154. presslord
2:44 AM GMT on June 22, 2008
My pwr out for 2 hrs on Johns Island due to storm. We`re headed to boat.to crank uo genny....and AC
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About JeffMasters

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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