The future of flooding

By: Dr. Jeff Masters , 10:06 PM GMT on February 19, 2008

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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

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.
Winter Flooding
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.
Yellow River Starke County Indiana

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99. lawntonlookers
4:01 PM GMT on February 20, 2008
Welcome home Atlantis

They indicated that USA 93 would probably be targeted for tonight at 0:00 GMT, but the weather may change it.

Thanks DR. Masters for the story on floods. The 100 year FEMA maps may have to be redone and restrict more areas from development. I know of several areas the have had several 100 year storms in the last 25 years.
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98. weathers4me
3:51 PM GMT on February 20, 2008
Mornin all. Glad to see Atlantis made it home safe and sound. Does anyone know when they plan on downing that satellite and will anyone be able to see it if they do it at night?
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96. seflagamma
9:54 AM EST on February 20, 2008
good morning Dr Master's and friends.

I think I am confused. We are in "global warming" phase but we will probably have record breaking cold for the 2008 winter (Dr Master's prev blog)... record cold for most of North America for Jan & Feb.

and I thought we were in a world wide drought now we are having flooding?

and I read else where that "ice age" we thought back in the 1970's that was coming..... really is coming after we get out of this little 20 year warming trend which is not going to be significant over time..and we will be really cold in about 40 years!

Does anyone really know (Except God) or are we all just giving it our best based on our own beliefs????
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93. cajunkid
8:20 AM CST on February 20, 2008
A few of us saw one of shuttles coming home while hunting one morning. We were amazed at how fast it went from horizon to horizon...very cool looking b/c the sun wasn't up yet, but it was reflecting off the shuttle and trail.
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92. aquak9
9:23 AM EST on February 20, 2008
we heard the boom last november? here in jacksonville. So cool that some of us heard it. aLways great when we get to share things together regardless of where we are.

and a lunar eclipse tonite! Wow!
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90. SWFLgazer
2:21 PM GMT on February 20, 2008
Where are you? Vort? Naples here.
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89. SWFLgazer
2:18 PM GMT on February 20, 2008
The boom was much stronger than others that I've experienced. This one really shook the house. Welcome home.
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86. aquak9
9:15 AM EST on February 20, 2008
COOL vort!!! that's so COOL!!!
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84. cajunkid
8:10 AM CST on February 20, 2008
Thats got to be a fun ride at the angle and speed they come home on!
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83. aquak9
9:12 AM EST on February 20, 2008
came in outta the southwest, from over cuba I think. was a GREAT touchdown!
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81. aquak9
9:08 AM EST on February 20, 2008
yay!!! picture perfect landing!!! wooo-hooo!!! and we all got to watch it together!!!
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79. sullivanweather
9:04 AM EST on February 20, 2008

They made it back safely!!!
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77. cajunkid
8:06 AM CST on February 20, 2008
man thats steep!
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70. cajunkid
7:40 AM CST on February 20, 2008
Patrap, thanks
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66. cajunkid
7:31 AM CST on February 20, 2008
anyone have the link to the shuttle tracker?
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65. sebastianjer
7:38 AM EST on February 20, 2008

I've never heard of this, and I've heard about pretty much everything weather-related at least once.

CRU's data was just released but here you go.

Click on this link it is the CRU Data set for the tempearature anomaly for the world going back to 1850, month by month. This is the readings that the IPCC uses. Scroll to the bottom, last number (column next to date) is for Jan 2008. Just go up and look at the drop since Jan, 2007.

or if you prefer here is a graph from one of them skeptic sites which shows it

As you can see, despite all the headlines of 2007 being the 2nd, 5th or 8th warmest IN THE HISTORY OF THE WORLD,depending on who's figure you believed, it was getting colder while doing it. satellite data doesn't show quite as big of drop, but then again it never has shown quite as big a rise. But that's not what your local newscast usually report, they usually report the GISS figures, which also show a drop. Have to go to work

Have a good day all
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64. sxwarren
11:54 AM GMT on February 20, 2008
Flooding isn't the only problem associated with heavy precip events. A couple years back, the Canadian wheat harvest was down about 17% due to saturated soils in the west. A series of heavy precip events, but no horrendous flooding, AFAIK.

Actual flooding is not required to screw up harvest quantity and quality enough to create significant socioeconomic consequences. And just how much is this being discussed compared to, say, building seawalls or reducing GHG emissions in 20-30 years? There are serious climate change consequences already on our doorstep that no one seems to be evaluating or planning mediation strategies for. No visuals suitable for CGI-representation in a summer blockbuster flick, I suppose.
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63. KoritheMan
10:50 AM GMT on February 20, 2008
From 1901-2000 global temperatures increased .6 degC globally. From Jan 2007 -to Jan 2008 global temperatures dropped .6 degC Actually .595 degC but what's five one hundredth of a degree amongst friends.

I've never heard of this, and I've heard about pretty much everything weather-related at least once.

Mind pointing me in the right direction to find this information?
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6:23 AM GMT on February 20, 2008
stormMan there are more people then it can support we are suffering the cannon ball effect
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5:52 AM GMT on February 20, 2008
iam more worry about this seasons ice melt in northern hemp it not as thick there fore it may melt even faster and in turn send even more colder water perkulating down into pacific
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60. StormMan
5:49 AM GMT on February 20, 2008
How about land use changes...that makes flooding all more real because you have all these people living in areas where none did 100+ years ago, so the "flooding" becomes more relevant. Plus the world's population has markedly increased in the past 100 years, hence there are more people that can be affected by the weather.

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59. MikeOhio
5:44 AM GMT on February 20, 2008
well the drumbeat for this blog continues.....

Seriously, there is just as much evidence that ths Sun has more influence on our weather cycles than anything else yet we rarely if ever hear about it here......

Oh well, onward and upward I guess....time to drive my mega-polluting SUV to stave off another winter storm here in Ohio hopefully :-D
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5:28 AM GMT on February 20, 2008
the great debate continues
funny thing by the time we figure it out its already going to be too late if not already
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57. sebastianjer
12:00 AM EST on February 20, 2008
Well Michael

The total increase in global temperatures for the entire 20th century was .6 degC globally. With the warmest year as everyone know being 1998 (EL Nino) Since 1998 temperature have not gone up, now have they?

That is going on a decade without an increase in global temperature. Now what is supposed to happen with increased CO2 ? Temperatures are supposed to rise, correct? They have not, I know you know this but i want to put this into perspective for anyone who just may be lurking.

I know that you are going to fill the screen with all kinds of charts and graphs and such, that's fine, I could do the same but I'm a simple guy.

The point is this, increased co2 should equal rising temperatures, for the past decade they have not.

But the point I really want to make is this.

From 1901-2000 global temperatures increased .6 degC globally. From Jan 2007 -to Jan 2008 global temperatures dropped .6 degC Actually .595 degC but what's five one hundredth of a degree amongst friends.

If (+).6 degC increase in 100 years is important what do you call (-) .6 degC in a single year?

I know you're going to blast that little analysis to pieces somehow, have fun, I'm going to bed. I thought that might just put a little perspective on things...or not

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55. sebastianjer
11:01 PM EST on February 19, 2008
Sounds good Michael what was the increase in temperature for the 20th century, do you know?
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53. ShenValleyFlyFish
10:15 PM EST on February 19, 2008
Jer thanks for the link. Downloaded it to read when clearer headed. Good night all.
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52. sebastianjer
10:19 PM EST on February 19, 2008
Excuse me Michael the news story you posted says snow storms in China I see where later it says southern China, I guess maybe some day we won't have cold winters in Southern China but it isn't twenty years after the onset of the global warming scare.

Since CRU just reported that Jan 2008 was the coldest month globally since Feb 1994, we'll just have to wait awhile to see.

BTW didn't see that little tid bit of info released on your nightly news now did you, lol

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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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