U.S. heavy precipitation events are increasing, but drought is not increasing

By: Dr. Jeff Masters , 2:04 PM GMT on March 17, 2009

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Last week, I introduced the National Climatic Data Center's Climate Extremes Index, which uses temperature and precipitation records to see if the U.S. climate is getting more extreme. Today, I'll focus on how the drought and precipitation extremes that go into the Climate Extremes Index have changed over the past century. The three precipitation-related factors to go into the Climate Extremes Index are:

1) The sum of (a) percentage of the United States in severe drought (equivalent to the lowest tenth percentile) based on the Palmer Drought Severity Index (PDSI) and (b) percentage of the United States with severe moisture surplus (equivalent to the highest tenth percentile) based on the PDSI.

2) Twice the value of the percentage of the United States with a much greater than normal proportion of precipitation derived from extreme (equivalent to the highest tenth percentile) 1-day precipitation events.

3) The sum of (a) percentage of the United States with a much greater than normal number of days with precipitation and (b) percentage of the United States with a much greater than normal number of days without precipitation.

Items 1 and 3 have shown no change in annual average value over the past century, but there has been a marked increase in the number of heavy 1-day precipitation events in recent decades. Thus, the record values of the Climate Extremes Index in recent years is due to a combination of the increase in heavy 1-day precipitation events, plus the increase in maximum and minimum temperatures.


Figure 1. The Annual Climate Extremes Index (CEI) for heavy 1-day precipitation events shows that these events, on average, have affected 10% of the U.S. over the past century (black line). However, heavy precipitation events have increased recently, with seven of the top ten years on record having occurred since 1995. Image credit: National Climatic Data Center.

Heavy precipitation events
Global warming theory predicts that global precipitation will increase, and that heavy precipitation events--the ones most likely to cause flash flooding--will also increase. This occurs because as the climate warms, evaporation of moisture from the oceans increases, resulting in more water vapor in the air. According to the 2007 Intergovernmental Panel on Climate Change (IPCC) report, water vapor in the global atmosphere has increased by about 5% over the 20th century, and 4% since 1970. The Climate Extremes Index plot for extreme 1-day precipitation events (Figure 1) does indeed show a sharp increase in heavy precipitation events in recent decades, with seven of the top ten years for these events occurring since 1995. The increases in heavy precipitation events have primarily come in the Spring and Summer, when the most damaging floods typically occur. This mirrors the results of Groisman et al. (2004), who found an increase in annual average U.S. precipitation of 7% over the past century, which has led to a 14% increase in heavy (top 5%) and 20% increase in very heavy (top 1%) precipitation events. 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.

Drought and extreme wetness
Global warming theory predicts that although global precipitation should increase in a warmer climate, droughts will also increase in intensity, areal coverage, and frequency (Dai et al., 2004). This occurs because when the normal variability of weather patterns brings a period of dry weather to a region, the increased temperatures due to global warming will intensify drought conditions by causing more evaporation and drying up of vegetation. Increased drought is my number one concern regarding climate change for both the U.S. and the world in the coming century. Two of the three costliest U.S. weather disasters since 1980 have been droughts--the droughts of 1988 and 1980, which cost $71 billion and $55 billion, respectively. The heat waves associated with these droughts claimed over 17,000 lives, according to the National Climatic Data Center publication, Billion-Dollar Weather Disasters. Furthermore, the drought of the 1930s Dust Bowl, which left over 500,000 people homeless and devastated large areas of the Midwest, is regarded to be the third costliest U.S. weather disaster on record, behind Katrina and the 1988 drought. (Ricky Rood has an excellent book on the Dust Bowl that he recommends in his latest blog post).


Figure 2. The Annual Climate Extremes Index (CEI) for drought. The worst U.S. droughts on record occurred in the 1930s and 1950s. There has been no trend in the amount of the U.S. covered by drought conditions (blue bars) or by abnormally moist conditions (red bars) over the past century. About 10% of the U.S. is typically covered by abnormally dry or wet conditions (black lines). Image credit: National Climatic Data Center.

The good news is that the intensity and areal coverage of U.S. droughts has not increased in recent decades (blue bars in Figure 2). The portion of the U.S. experiencing abnormal drought and exceptionally wet conditions has remained nearly constant at 10% over the past century. A recent paper by Andreadis et al., 2006, summed up 20th century drought in the U.S. thusly: "Droughts have, for the most part, become shorter, less frequent, and cover a smaller portion of the country over the last century. The main exception is the Southwest and parts of the interior of the West, where, notwithstanding increased precipitation (and in some cases increased soil moisture and runoff), increased temperature has led to trends in drought characteristics that are mostly opposite to those for the rest of the country especially in the case of drought duration and severity, which have increased."

The rest of the globe has not been so lucky. Globally, Dai and Trenberth (2004) showed that areas experiencing the three highest categories of drought--severe, extreme, and exceptional--more than doubled (from ~12 to 30%) since the 1970s, with a large jump in the early 1980s due to an El Niño-related precipitation decrease over land, and subsequent increases primarily due to warming temperatures. According to the Global Drought Monitor, 50 million people world-wide currently live in areas experiencing the highest level of drought (exceptional).

The future of U.S. drought
As the climate continues to warm, I expect the frequency, severity, and areal coverage of droughts to increase over the U.S. We're certainly off to a dry start in 2009--the period January - February this year was the driest such period in U.S. history, according to the National Climatic Data Center.

References
Andreadis, K. M. Lettenmaier, D. P., "Trends in 20th century drought over the continental United States", Geo. Res. Letters 33, 10, L10403, DOI 10.1029/2006GL025711

Dai A., K.E. Trenberth, and T. Qian, 2004: A global data set of Palmer Drought Severity Index for 18702002: Relationship with soil moisture and effects of surface warming", J. Hydrometeorol., 5, 11171130.

Gleason, K.L., J.H. Lawrimore, D.H. Levinson, T.R. Karl, and D.J. Karoly, 2008: "A Revised U.S. Climate Extremes Index", J. Climate, 21, 2124-2137.

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.

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.

Jeff Masters

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401. Patrap
5:49 PM GMT on May 12, 2009
SURA-SCOOP
Member Since: July 3, 2005 Posts: 414 Comments: 125613
400. Patrap
8:33 PM GMT on April 17, 2009







Voluntary Versus Mandatory
Evacuations


Last Updated: January 29, 2008 ast Updated: January 29, 2008 Related resource areas: Family Caregiving

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Voluntary Versus Mandatory Evacuation

The Federal Emergency Management Agency defines evacuations as the organized, phased and supervised movement of people from dangerous or potentially dangerous areas. Some evacuations occur without the direction of government officials. This happens when residents either perceive of or are aware of an actual emergency and evacuate an area on their own. Voluntary and Mandatory/Directed Evacuations involve government direction.

The definitions for these follow:


Member Since: July 3, 2005 Posts: 414 Comments: 125613
399. Skyepony (Mod)
12:34 PM GMT on March 20, 2009
I still can't believe they didn' plant all that..94 % of U.S. tomatoes and 89 % of U.S. carrots are grown there for that time of year. And the home garden seeds are beginning to come up in short supply (as predicted).
Member Since: August 10, 2005 Posts: 156 Comments: 36105
398. surfmom
10:07 AM GMT on March 20, 2009
Quoting Skyepony:
Despair as California's Central Valley dries up
FIREBAUGH, California a ' "Now we know how the Indians felt," sighed Jim Diedrich, a farmer who said he was betrayed by the government as California's Central Valley reels from a serious drought.



They've only just begun to know how our Native Americans felt.
Member Since: July 18, 2007 Posts: 30 Comments: 26536
397. surfmom
10:04 AM GMT on March 20, 2009
WELCOMING SPRING AT 7:43 AM
Member Since: July 18, 2007 Posts: 30 Comments: 26536
396. natrwalkn
8:41 AM GMT on March 20, 2009
The previous comment was intended as a response to 352.
Member Since: August 14, 2008 Posts: 0 Comments: 67
395. natrwalkn
8:37 AM GMT on March 20, 2009
Massive earthquakes can happen in areas where they are least expected. The great Charleston earth quake had no tremmors to forewarn of the impending seismic event. There are many faults under the coastal plain of the the SE United States that are unknown because they are buried by sand and sediment. We know they are there when they break and cause an earthquake. In the west, the continental bedrock is exposed, faults are easily seen, and their behavior is becoming fairly predictable. Not so here on the Atlantic coastal plain. Sweet Dreams.
Member Since: August 14, 2008 Posts: 0 Comments: 67
394. natrwalkn
8:22 AM GMT on March 20, 2009
Quoting TheWeatherMan504:
Joe Bastardi at Accuweather just posted this for his highest paying clients...



HAHA!! So true! Dr. Gray, take notes.
Member Since: August 14, 2008 Posts: 0 Comments: 67
393. KEHCharleston
6:27 AM GMT on March 20, 2009
URGENT - WEATHER MESSAGE
NATIONAL WEATHER SERVICE CHARLESTON SC
114 AM EDT FRI MAR 20 2009

SCZ045-050-201200-
/O.NEW.KCHS.SM.Y.0001.090320T0514Z-090320T1200Z/
BERKELEY-CHARLESTON-
INCLUDING THE CITIES OF...MONCKS CORNER...CHARLESTON
114 AM EDT FRI MAR 20 2009

...DENSE SMOKE ADVISORY IN EFFECT UNTIL 8 AM EDT THIS MORNING...

THE NATIONAL WEATHER SERVICE IN CHARLESTON HAS ISSUED A DENSE
SMOKE ADVISORY...WHICH IS IN EFFECT UNTIL 8 AM EDT THIS MORNING.

THE SOUTH CAROLINA STATE FORESTRY SERVICE HAS ANNOUNCED THAT
DENSE SMOKE WAS CAUSING ROAD CLOSURES IN THE FRANCIS MARION
NATIONAL FOREST AREA. THE ROAD CLOSURE CHECKPOINTS EXTEND FROM
NEAR STEED CREEK ROAD...SR 133 TO HALFWAY CREEK ROAD WEST TO
HIGHWAY 41. VISIBILITIES WERE LESS THAN A QUARTER MILE...EVEN
NEAR ZERO LOCALLY.

VISIBILITIES SHOULD IMPROVE AROUND OR BEFORE DAWN FRI AS A COLD
FRONT MOVES THROUGH AND NORTHERLY WINDS INCREASE.

A DENSE SMOKE ADVISORY MEANS FIRES WILL CREATE SMOKE THICK ENOUGH
TO GREATLY REDUCE VISIBILITIES. MOTORISTS SHOULD DRIVE WITH
CAUTION AND ALLOW FOR EXTRA TRAVEL TIME. USE LOW BEAM HEADLIGHTS
AND REDUCE DRIVING SPEEDS. LEAVE PLENTY OF DISTANCE AHEAD OF YOU
IN CASE A SUDDEN STOP IS NEEDED.

Member Since: August 19, 2008 Posts: 6 Comments: 2490
392. KoritheMan
5:48 AM GMT on March 20, 2009
390.

No, because SSTs in that area don't reach their peak until September.
Member Since: March 7, 2007 Posts: 521 Comments: 19127
391. Skyepony (Mod)
4:41 AM GMT on March 20, 2009
Despair as California's Central Valley dries up
FIREBAUGH, California a ' "Now we know how the Indians felt," sighed Jim Diedrich, a farmer who said he was betrayed by the government as California's Central Valley reels from a serious drought.

Member Since: August 10, 2005 Posts: 156 Comments: 36105
390. JRRP
4:37 AM GMT on March 20, 2009
Do you think that this is important right now?
Member Since: August 16, 2007 Posts: 0 Comments: 5082
389. Skyepony (Mod)
3:37 AM GMT on March 20, 2009
Here's a satellite picture of that volcano near fiji that went off under water near the earthquake.
Member Since: August 10, 2005 Posts: 156 Comments: 36105
388. TampaSpin
3:18 AM GMT on March 20, 2009
Member Since: September 2, 2007 Posts: 177 Comments: 20430
387. KoritheMan
2:47 AM GMT on March 20, 2009
An interesting excerpt I found from the article linked to by atomaggie:

the 1924 Cuba hurricane that struck as a Category 5 (and is now the first recorded Category 5 hurricane in the database).

I still wonder how many storms were underestimated back before the satellite era, particularly those out at sea, although I suspect there were some hurricanes at landfall that were underestimated, as well.
Member Since: March 7, 2007 Posts: 521 Comments: 19127
386. KoritheMan
2:44 AM GMT on March 20, 2009
Quoting atmoaggie:
Who was asking about the reanalysis project data in the 1920s

Just announced that Landsea et al have posted new data, through 1925.

http://www.aoml.noaa.gov/hrd/data_sub/re_anal.html


I believe that was 1900hurricane, who is a Texas resident.
Member Since: March 7, 2007 Posts: 521 Comments: 19127
385. atmoaggie
2:37 AM GMT on March 20, 2009
Who was asking about the reanalysis project data in the 1920s?

Just announced that Landsea et al have posted new data, through 1925.

http://www.aoml.noaa.gov/hrd/data_sub/re_anal.html
Member Since: August 16, 2007 Posts: 6 Comments: 12461
384. Skyepony (Mod)
2:34 AM GMT on March 20, 2009
Major flooding in IL
Member Since: August 10, 2005 Posts: 156 Comments: 36105
383. Skyepony (Mod)
2:30 AM GMT on March 20, 2009
Looks like Former Oregon State University marine biologist Jane Lubchenco is the new head of NOAA.
Member Since: August 10, 2005 Posts: 156 Comments: 36105
382. Orcasystems
2:26 AM GMT on March 20, 2009
Complete Blog Refresh, with New Weather/CritterCam
Current Home weather station data.

Zoo is finally out of the rain :)

Member Since: October 1, 2007 Posts: 81 Comments: 26493
381. AussieStorm
2:25 AM GMT on March 20, 2009

Queensland braces for weekend cyclone
Article from: NEWS.com.au

March 20, 2009

NORTH and central Queensland will be on cyclone alert over the weekend as the weather bureau monitors a tropical low about 600km northeast of Mackay.

The forecast comes three years to the day after cyclone Larry crossed the North Queensland coast, devastating the town of Innisfail.

Bureau of Meteorology senior forecaster Ben Annells said the low pressure system was interacting with an upper level trough that was keeping it steady.

But when the trough moves away it could intensify over the weekend into a cyclone, expected to be called Jasper.

"It looks like it will stay over the Coral Sea into the weekend, but its long-term movement is uncertain,'' Mr Annells said.

"It depends on the interaction with another upper trough next week.''

Strong winds of up to 33 knots are already being felt from Cooktown to Sandy Cape, with seas to three metres in open waters and outside the reef.

"The environment at the moment is favourable for a cyclone,'' Mr Annells said.

"It's not unusual to get cyclones this time of the year and even into April.
Member Since: September 30, 2007 Posts: 9 Comments: 15749
380. Skyepony (Mod)
2:25 AM GMT on March 20, 2009
Fargo is expecting a 40' river crest, emergancy flood stage is like 30'..they have about a week to get ready. Officials have identified 13 neighborhoods in Fargo along the Red River corridor and five along the city's southwest side that need protection. They've put in orders for more than 2 million sandbags.
Member Since: August 10, 2005 Posts: 156 Comments: 36105
379. atmoaggie
2:22 AM GMT on March 20, 2009
Houston Chron blogger Eric Berger: Bastardi's seasonal forecast for 2007 was "doom and death," and he noted, "Bastardi doesn't predict specific numbers. His chief currency is fear."
Member Since: August 16, 2007 Posts: 6 Comments: 12461
378. all4hurricanes
2:21 AM GMT on March 20, 2009
357 didn't Laura form outside that zone making even that prediction wrong
Member Since: March 29, 2008 Posts: 0 Comments: 2338
377. hahaguy
2:21 AM GMT on March 20, 2009
Quoting Drakoen:


loving the irony in that name lol.


Ya his name represents what he his LMAO
Member Since: August 12, 2007 Posts: 2 Comments: 2838
376. Drakoen
2:17 AM GMT on March 20, 2009
Quoting Chicklit:
Is Bastardi his real last name?!


loving the irony in that name lol.
Member Since: October 28, 2006 Posts: 57 Comments: 29714
375. TampaSpin
2:09 AM GMT on March 20, 2009
Hope everyone realizes that POST 357 was a JOKE.....ROFLMAO
Member Since: September 2, 2007 Posts: 177 Comments: 20430
374. futuremet
1:58 AM GMT on March 20, 2009
"This area could see more or less activity than 2008"

LOL OBVIOUSLY
Member Since: July 19, 2008 Posts: 43 Comments: 4051
373. Ossqss
1:26 AM GMT on March 20, 2009
Quoting atmoaggie:


Keep looking. Do not sleep until you find it.

"A failure establishes only this, that our determination to succeed was not strong enough."
-- Hoshang N. Akhtar
\\

Will do, - you always miss 100% of the shots you don't take --- EZE----.
Member Since: June 12, 2005 Posts: 6 Comments: 8183
372. atmoaggie
1:20 AM GMT on March 20, 2009
Quoting Ossqss:


I just cannot seem to find this anywhere /? How about a link ? ®¿ª


Keep looking. Do not sleep until you find it.

"A failure establishes only this, that our determination to succeed was not strong enough."
-- Hoshang N. Akhtar
Member Since: August 16, 2007 Posts: 6 Comments: 12461
371. Ossqss
1:07 AM GMT on March 20, 2009
Quoting TheWeatherMan504:
Joe Bastardi at Accuweather just posted this for his highest paying clients...



I just cannot seem to find this anywhere /? How about a link ? ®¿ª
Member Since: June 12, 2005 Posts: 6 Comments: 8183
370. rainmound
12:42 AM GMT on March 20, 2009
Quoting CybrTeddy:


Your right, its actually intensified in the past few weeks. Dramatically, and it could presist into the heart of the season. Joe B saying that the season would be less active pretty much confirms to me my worst fears, this will be an active season.


Member Since: April 18, 2006 Posts: 0 Comments: 42
369. Ossqss
12:36 AM GMT on March 20, 2009
#357 --

Please note that the orb in front of you could produce a Hurricane sooner or later somewhere.

Member Since: June 12, 2005 Posts: 6 Comments: 8183
368. Chicklit
12:34 AM GMT on March 20, 2009
Dry as a bone here in east Central Florida. We had a few sprinkles today. Just enough to evaporate. Rip currents predicted for the beach this weekend.
Member Since: July 11, 2006 Posts: 14 Comments: 11047
367. Chicklit
12:32 AM GMT on March 20, 2009
Is Bastardi his real last name?!
Member Since: July 11, 2006 Posts: 14 Comments: 11047
366. MarvellousLoch
12:30 AM GMT on March 20, 2009
In other words Joe Bastardi is saying that 2009 will be different to 2008. The great fascination with the weather is that one year is never like any other!!
365. vortfix
12:26 AM GMT on March 20, 2009
#357....LMAO!!

364. lhwhelk
12:24 AM GMT on March 20, 2009
Re Bastardi Forecast:
Surely you can tell a joke when you see one!
Member Since: August 26, 2008 Posts: 0 Comments: 63
363. HurricaneSwirl
12:14 AM GMT on March 20, 2009
357. Wow... that's pretty much saying anything
can happen... and doesn't everyone know that after the past 5, 10, 15 years???
Member Since: July 7, 2008 Posts: 2 Comments: 3237
362. futuremet
11:24 PM GMT on March 19, 2009
Great site Tampa
Member Since: July 19, 2008 Posts: 43 Comments: 4051
361. TampaSpin
11:06 PM GMT on March 19, 2009
This is my forecasted I posted Wednesday at 9:50am

TampaSpins Forecast Link
Member Since: September 2, 2007 Posts: 177 Comments: 20430
360. MisterPerfect
10:53 PM GMT on March 19, 2009
Quoting TheWeatherMan504:
Joe Bastardi at Accuweather just posted this for his highest paying clients...



He sounds like a betting man to me..
Member Since: November 1, 2006 Posts: 71 Comments: 20123
359. MisterPerfect
10:47 PM GMT on March 19, 2009
Is there any more rain the stationary front over south Florida might produce? Need it. Can't see anymore for weeks and weeks ahead..
Member Since: November 1, 2006 Posts: 71 Comments: 20123
358. futuremet
10:45 PM GMT on March 19, 2009
Quoting SevereHurricane:
Wow FutureMet good forecast...
Well put,
I enjoyed it...


Thanks

it was not exactly a forecast though..
Member Since: July 19, 2008 Posts: 43 Comments: 4051
357. TheWeatherMan504
10:35 PM GMT on March 19, 2009
Joe Bastardi at Accuweather just posted this for his highest paying clients...

Member Since: May 18, 2008 Posts: 2 Comments: 1042
356. SevereHurricane
10:32 PM GMT on March 19, 2009
Wow FutureMet good forecast...
Well put,
I enjoyed it...
Member Since: September 7, 2008 Posts: 17 Comments: 1604
355. futuremet
9:57 PM GMT on March 19, 2009
Quoting RitaEvac:
Severe outbreak next week, be getting ready, first big spring storm system is ready to rock and roll.

After seeing the past GFS runs, my adrenaline rekindled. That feeling is quite nostalgic, it reminds me of hurricane season.

A rapidly amplifying longwave trough is expected to move in across the midwest around Monday and tuesday. The robust structure of this structure will help enhance the flow of positive vorticity advection which catalyzes cyclogenesis. The "U" structure is clearly evident on the model forecasts, and the 850mb range is showing plenty of warm air propagating northward during monday and tuesday.

Severe weather is a possible next week, however, I am still reluctant to consider this as an "outbreak", hence, I'll wait for about 48 hours to draw any real conclusions.





LI Index



Member Since: July 19, 2008 Posts: 43 Comments: 4051
354. Ossqss
9:46 PM GMT on March 19, 2009
Quoting TampaSpin:
I have a good section on my web site on Earthquakes and Tsunami Section.

TampaSpins Link


Well done Tampa. Looks good.
Member Since: June 12, 2005 Posts: 6 Comments: 8183
353. HIEXPRESS
9:38 PM GMT on March 19, 2009
344. vortfix

Cyclone Phase Analysis (GFS)

351. RitaEvac
Yep

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK


84 Hour 225 mb wind prog

http://adds.aviationweather.gov/winds/
Member Since: October 13, 2005 Posts: 4 Comments: 2155
352. Ossqss
9:37 PM GMT on March 19, 2009
Quoting Starwoman:



That chart shows all earthquakes of M1 and higher.
Those are so small, you would hardly feel them.
It looks worse than it is... *s*


Key word "Hardly". The ground still moves under the feet and I can't fly, so I will take my Hurricanes (since I can see them coming) and leave the shake rattle and rolling to others. :^)
Member Since: June 12, 2005 Posts: 6 Comments: 8183
351. RitaEvac
9:30 PM GMT on March 19, 2009
Severe outbreak next week, be getting ready, first big spring storm system is ready to rock and roll.
Member Since: July 14, 2008 Posts: 1 Comments: 9625

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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.