Dr. Jeff Masters' WunderBlog

The future of flooding

Posted by: Dr. Jeff Masters, 22:06 GMT le 19 février 2008

Are storms getting more extreme due to climate change? That is a difficult question to answer, since reliable records are not available at all in many parts of the world, and extend back only a few decades elsewhere. However, we do have a fairly good set of precipitation records for many parts of the globe, and those records show that the heaviest types of rains--those likely to cause flooding--have increased in recent years. 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. Satellite measurements (Trenberth et al., 2005) have shown a 1.3% per decade increase in water vapor over the global oceans since 1988. Santer et al. (2007) used a climate model to study the relative contribution of natural and human-caused effects on increasing water vapor, and concluded that this increase was "primarily due to human-caused increases in greenhouse gases". This was also the conclusion of Willet et al. (2007).

More water vapor equals more precipitation
This increase in water vapor has very likely led to an increase in global precipitation. For instance, 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, there is a large natural variation in extreme precipitation events.

Pollution may contribute to higher precipitation
It is possible that increased pollution is partly responsible for the increase in precipitation and in heavy precipitation events in some parts of the world. According to Bell et al. (2008), summertime rainfall over the Southeast U.S. is more intense on weekdays than on weekends, with Tuesdays having 1.8 times as much rain as Saturdays during the 1998-2005 period analyzed. Air pollution particulate matter also peaks on weekdays and has a weekend minimum, making it likely that pollution is contributing to the observed mid-week rainfall increase. Pollution particles act as "nuclei" around which raindrops condense, increasing precipitation in some storms.

The future of flooding
It is difficult to say if the increase in heavy precipitation events in recent years has led to more flooding, since flooding is critically dependent on how much the landscape has been altered by development, upstream deforestation, and what kind of flood control devices are present. One of the few studies that did attempt to quantify flooding (Milly et al., 2002) found that the incidence of great floods has increased in recent decades. In the past century, the world's 29 largest river basins experienced a total of 21 "100-year floods"--the type of flood one would expect only once per 100 years in a given river basin. Of these 21 floods, 16 occurred in the last half of the century (after 1953). With the IPCC predicting that heavy precipitation events are very likely to continue to increase, it would be no surprise to see flooding worsen globally in the coming decades.

Jeff Masters

References
Bell, T. L., D. Rosenfeld, K.-M. Kim, J.-M. Yoo, M.-I. Lee, and M. Hahnenberger (2008), "Midweek increase in U.S. summer rain and storm heights suggests air pollution invigorates rainstorms," J. Geophys. Res., 113, D02209, doi:10.1029/2007JD008623.

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.

Milly, P.C.D., R.T. Wetherald, K.A. Dunne, and T.L.Delworth, Increasing risk of great floods in a changing climate", Nature 415, 514-517 (31 January 2002) | doi:10.1038/415514a.

Santer, B.D., C. Mears, F. J. Wentz, K. E. Taylor, P. J. Gleckler, T. M. L. Wigley, T. P. Barnett, J. S. Boyle, W. Brüggemann, N. P. Gillett, S. A. Klein, G. A. Meehl, T. Nozawa, D. W. Pierce, P. A. Stott, W. M. Washington, and M. F. Wehner, 2007, "Identification of human-induced changes in atmospheric moisture content", PNAS 2007 104: 15248-15253.

Trapp, R.J., N.S. Diffenbaugh, H.E. Brooks, M.E. Baldwin, E.D. Robinson, and J.S. Pal, 2007, Severe thunderstorm environment frequency during the 21st century caused by anthropogenically enhanced global radiative forcing, PNAS 104 no. 50, 19719-19723, Dec. 11, 2007.

Trenberth, K.E., J. Fasullo, and L. Smith, 2005: "Trends and variability in column-integrated atmospheric water vapor", Climate Dynamics 24, 741-758.

Willett, K.M., N.P. Gillett, P.D. Jones, and P.W. Thorne, 2007, "Attribution of observed surface humidity changes to human influence", Nature 449, 710-712 (11 October 2007) | doi:10.1038/nature06207.

Winter Flooding (Jmroh)

This is the result of extreme snowmelt and 4 inches of rain.

Yellow River Starke County Indiana (StarkeHistorian)

Kankakee Game Preserve, 10 Mile Road: The Yellow River crested this morning at 12.14' at the US35 bridge at 11:45AM. This was 2.14' over flood stage. The record is 15.3 Jan 1, 1991.

Categories: Climate Change Flood

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302. CybrTeddy 17:30 GMT le 24 février 2008
We are at T-4 Months 6 days and 11:30 hours intill the 2008 hurricane season. The WeatherUnderGround now deciding a Go-No Go for start of Pre-hurricane season forcasts. At the T-1 Month start we are go/no go for an eariler start to the hurricane season. This is Weatherunderground Control. The possibilty for a Pre-Season system in looks at this time, with a go/no-go system up for this at around the 1 Month mark. Member Since: 8 juillet 2005 Posts: 253 Comments: 20276

304. Cavin Rawlins 17:33 GMT le 24 février 2008
289. JFV 1:12 PM AST on February 24, 2008 Hey Weather456, could we expect to see severe weather down here on Wednesday afternoon, prior to that very potent cold front moving through? if is FL u live, then scattered t-storms with a 30% chance of severe weather, warm Feb 24-29. I feel that its a good chance knowing the warm-air adevection will be larger than normal. Member Since: 24 juillet 2005 Posts: 407 Comments: 19076

305. Patrap 17:34 GMT le 24 février 2008
JFV heres a NOAA link for that, suggest bookmarking this puppy. Link Member Since: 3 juillet 2005 Posts: 372 Comments: 111622

306. Patrap 17:36 GMT le 24 février 2008
March,April,May..Thats 90 days right there according to my calender..a lil more than 100 days I believe to H-saeason Member Since: 3 juillet 2005 Posts: 372 Comments: 111622

308. Patrap 17:40 GMT le 24 février 2008
..anytime JFV, Glad to contribute. Member Since: 3 juillet 2005 Posts: 372 Comments: 111622

310. Cavin Rawlins 17:44 GMT le 24 février 2008
298. JFV 1:28 PM AST on February 24, 2008 Hey Patraph what's the current position of the bermuda high, out in the Atlantic Ocean right now? I know I'm not Patrap but the Azores High is the dominate high right now. Ususally this time, the Bermuda High is transitory in nature due those strong cold front pushing off the US East Coiast. Right now there is cold front pushing across the area then the high will build up again. But the question is- is that really the Bermuda High? or should we call it the Bermuda High? I'm not sure becuz the Bermuda High is tall and maintained by subsidence. Those transitory highs are cold core in nature and shallow, usually not extending upwards more than 600 mb. Member Since: 24 juillet 2005 Posts: 407 Comments: 19076

311. Patrap 17:45 GMT le 24 février 2008
Every year brings the same threat of a strike. Number of storms dont necessarily mean more Impacts..and a slow year dosent mean any less of a Threat. Andrew in 92 is a good example of the latter. Big storm, Bad impact..and the A storm it was..a late starting season 92 was. Preparation is the Key to being ready for whatever the season brings. Member Since: 3 juillet 2005 Posts: 372 Comments: 111622

312. Cavin Rawlins 17:47 GMT le 24 février 2008
we have to wait alot more. The time we waited from Nov 30 to now is approx. 3 months...we have another 3 months to go. Member Since: 24 juillet 2005 Posts: 407 Comments: 19076

315. CybrTeddy 17:50 GMT le 24 février 2008
As you all remember, in 2007, the US was sparred, because the Carribian was shreaded by 2 CAT 5 hurricanes within a few weeks. Member Since: 8 juillet 2005 Posts: 253 Comments: 20276

317. hahaguy 17:51 GMT le 24 février 2008
lets just put it this way . This season i'm going to be watching the bermuda high very closely and hopefully not have another 2004. Member Since: 12 août 2007 Posts: 2 Comments: 2838

320. Cavin Rawlins 17:55 GMT le 24 février 2008
317. hahaguy 1:51 PM AST on February 24, 2008 lets just put it this way . This season i'm going to be watching the bermuda high very closely and hopefully not have another 2004. yep...also watch the position and movement of the climatological upper trof over the Eastern US. That cud help recurve most storms to spare u guys this yr. Member Since: 24 juillet 2005 Posts: 407 Comments: 19076

321. hahaguy 17:56 GMT le 24 février 2008
i almost forgot about that 456 good point. Member Since: 12 août 2007 Posts: 2 Comments: 2838

322. Patrap 17:58 GMT le 24 février 2008
The blog here usually gets pretty hectic during landfalling canes ,but the wunderground only provides what you see. Info. Jeff Masters entry here August 28th 2005 entry Link Member Since: 3 juillet 2005 Posts: 372 Comments: 111622

324. hahaguy 18:00 GMT le 24 février 2008
god patrap i remember the past few years it was like a madhouse in here. all of the wishcasters are in here and you get really aggrivated. Member Since: 12 août 2007 Posts: 2 Comments: 2838

326. NorthxCakalaky 01:22 GMT le 25 février 2008
Snow showers in N.C mountains. Accumalation around 2inches along the western slopes.Other mountain areas could see around a inch.Eastern slopes - Flurries/Sprinkles.Moisture is mainly limited to around 1500f.t to 4000 f.t.Below should be partly cloudy. Also, V.A,T.N and W.V could see snow showers in the mountain areas.

327. CybrTeddy 01:30 GMT le 25 février 2008
This is Weatherunderground control at T- 4 Months and counting, the first forcasts from the weather underground Mission Controlers now begining to start pre-season forcast's for this years Atlantic Hurricane season, this is Weatherunderground Control. Member Since: 8 juillet 2005 Posts: 253 Comments: 20276

335. Patrap 03:25 GMT le 25 février 2008
Your Tax dollars at work now, and more. Link NOAA 2008 Budget Link Member Since: 3 juillet 2005 Posts: 372 Comments: 111622

336. ShenValleyFlyFish 03:46 GMT le 25 février 2008
My FEMA trailer RANT: Link Member Since: 9 septembre 2007 Posts: 36 Comments: 4684

337. KoritheMan 04:19 GMT le 25 février 2008
god patrap i remember the past few years it was like a madhouse in here. all of the wishcasters are in here and you get really aggrivated. I've learned my lesson about that. Just ignore wishcasters and downcasters. Not necessarily put them on your Ignore List, but if they repeatedly wishcast and downcast, I'll do it this season. What I want is a good, helpful, and civil discussion about the tropics during hurricane season. Not a rant about a storm forming or not forming. I've learned not to argue with people anymore either. Member Since: 7 Mars 2007 Posts: 411 Comments: 15473

338. Tazmanian 04:46 GMT le 25 février 2008
337. KoritheMan 8:19 PM PST on February 24, 2008 god patrap i remember the past few years it was like a madhouse in here. all of the wishcasters are in here and you get really aggrivated. I've learned my lesson about that. Just ignore wishcasters and downcasters. Not necessarily put them on your Ignore List, but if they repeatedly wishcast and downcast, I'll do it this season. What I want is a good, helpful, and civil discussion about the tropics during hurricane season. Not a rant about a storm forming or not forming. I've learned not to argue with people anymore either same here Member Since: 21 mai 2006 Posts: 5088 Comments: 111360

340. surfmom 15:00 GMT le 25 février 2008
Wow you guys are far more interesting then the newspaper this morning. Great piece StormW and Taz...yes you have the right perspective on things. My favorite quote" NEVER TRY TO TEACH A PIG TO SING, IT ONLY ANNOYS THE PIG AND FUSTRATES YOU" With that said, in my search for upcoming waves (tues afternoon-wednesday am,Gomex) I noticed that the water by me SRQ is 72 degrees & 69 degrees up in Tampa --I don't think I recall such a warm gulf ever at this time of year --may be wrong on this will start to check this out --but it seems like the gulf is mighty warm already. Member Since: 18 juillet 2007 Posts: 30 Comments: 26538

341. NEwxguy 15:07 GMT le 25 février 2008
with this neverending winter here in the northeast,its nice to get some tropical discussions started even if its a litte premature. Member Since: 6 septembre 2007 Posts: 816 Comments: 13132

343. surfmom 15:30 GMT le 25 février 2008
newxweatherguy, we are rockin HOT down here. Polo season is held in FL as they figure temps. in the 70's. Yesterday's polo match was a test of heat endurance. While we usually body clip the horses just once in the season...we are all groaning as it looks like we are going to have to clip again (a very tedious job that neither horse or groom enjoys) although we do it because the horses can cool far more rapidly with less of a coat. Light NOT temperature signals the horse's body to keep a winter coat. Once we have longer daylight they begin to shed to a lighter summer coat. but they are still, based on light, in the winter fur growing mode --so it's more work for us. Especially with this early heat. The weather is very influential regarding health issues as well. Going rapidly from HOT to cold (when these fronts come in) is a real instigator for colic - which can actually kill a horse. As well as the reverse quick changes from cold to hot, because then the horses have not stayed hydrated enough (they drink less in the cold) to handle the sudden extreme heat. Worse for us here in FL is the drought. ALL pastures are suffering and not replenishing good grass, even when the pastures are "resting". Hay bales, alfalfa, prices are off the wall due to shortages, high demand =-poor pastures so we must supplement, as well as increase fuel prices trickling down the ladder. The very wealthy can ride this out, but the middle guys are seriously hurting. In theory I always knew how important weather is in regards to history and the actions of humans and animals. Now that i work so closely with horses the theory is a very big and sobering reality Member Since: 18 juillet 2007 Posts: 30 Comments: 26538

345. surfmom 15:30 GMT le 25 février 2008
Good morning StormW!!!! here for just a bit this AM --Good to see you Member Since: 18 juillet 2007 Posts: 30 Comments: 26538

347. Patrap 15:40 GMT le 25 février 2008
Member Since: 3 juillet 2005 Posts: 372 Comments: 111622

349. taistelutipu 16:04 GMT le 25 février 2008
Hi everyone, first of all I have to agree with surfmom, the blog is very informative today. Thank you very much for the input on the relations between weather events and horses and the concise outlooks for the 2008 season and other weather stuff. I enjoyed reading it. 337. KoritheMan 8:19 PM PST on February 24, 2008 god patrap i remember the past few years it was like a madhouse in here. all of the wishcasters are in here and you get really aggrivated. I've learned my lesson about that. Just ignore wishcasters and downcasters. Not necessarily put them on your Ignore List, but if they repeatedly wishcast and downcast, I'll do it this season. What I want is a good, helpful, and civil discussion about the tropics during hurricane season. Not a rant about a storm forming or not forming. I've learned not to argue with people anymore either During high season I used to click on the [-] button in the upper right corner of each post if I decide that the post is not worth to be read. This way I can shorten each page significantly and I have a good overview who is constantly wishcasting or downcasting since in this case I only see message header with the username and the time of the post. Once I have more than 10 of the same person in one blog entry that's the yellow card and if that happens again it's the red -> latest addition on my ignore list. This system worked quite well last season and it helped me to reduce 3000 or more comments on one blog entry occasionally by a quarter or even more. Let's see how things will turn out after June 1st, I hope for a smaller number of trolls and wishcasters. Greetings from sunny Helsinki tipsku Member Since: 20 août 2007 Posts: 10 Comments: 566

350. weatherboyfsu 16:06 GMT le 25 février 2008
Good morning, Thanks StormW for posting the outlook......Another round of Thunderstorms should be coming thru the florida area tomorrow..........More rain!!!!! This winter has been great! I know that it will get cold on Wednesday but thats minor in the grand scheme of things. Everyone in florida should keep an eye on your local weather reports in case the atmosphere sharpens up a bit. Have a good week! Member Since: 17 juillet 2005 Posts: 0 Comments: 1025

351. LakeShadow 16:26 GMT le 25 février 2008
Hey folks! How's it going? We've been white here for a few weeks, last week Tuesday's lake effect event taught us that the 80% frozen over lake can still pack a punch with the snow totals as we got about 13" at my house. As per tropical discussions, I was wondering what with this moderate-strong La Nina still cranking away, if there was not perhaps some potential for an early start to the tropical season... La Nina sure messed with the NE winter! What havoc will she reak this spring? And when is she going away???? Member Since: 10 août 2007 Posts: 3 Comments: 2134

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