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

By: Dr. Jeff Masters , 3:12 PM GMT on January 25, 2011

Share this Blog
2
+

Yesterday, 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) the monthly percentage of the United States in severe drought (equivalent to the lowest tenth percentile) based on the Palmer Drought Severity Index (PDSI) and (b) the 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 and near-record values of the Climate Extremes Index in recent years have been due to a combination of the increase in heavy 1-day precipitation events and an 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 in recent decades. The seven most extreme years since 1910 have all occurred since 1995, with 2010 ranking as the 5th most extreme year in the past 100 years. 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, and 2010 coming in 5th place in the past 100 years. 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. Increases in drought and flooding are my top two concerns 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 a 2008 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. like this: "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."

Other portions of the globe have not not been so fortunate. 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 NiƱo-related precipitation decrease over land, and subsequent increases primarily due to warming temperatures. According to the Global Drought Monitor, 98 million people world-wide currently live in areas experiencing the highest level of drought (exceptional).

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.

A new Nor'easter for New England
A low pressure system currently centered along the Gulf Coast near New Orleans is bringing heavy rain to much of the south. Rains in excess of 3 inches have fallen over central Mississippi, and the rain is expected to change to snow over northern Mississippi, northern Alabama, and much of Tennessee late tonight. A swath of 2 - 4" of snow is expected in these regions, with higher amounts in the mountains. The low will move off the coast of North Carolina on Wednesday morning, then northeastward out to sea, potentially bringing heavy snows of 4 - 8" to inland portions of New England and the mid-Atlantic. At this time, it appears that the storm will track far enough from the coast and there will be insufficient cold air in place for snowfall amounts of a foot or more to fall. A nasty mix of rain, sleet, and snow is likely for much of the coast, with the heaviest snows expected to miss New York City, Washington D.C., and Boston (Figure 3.) As the low drags its cold front over Florida this afternoon, a slight risk of severe thunderstorms exists, and Florida could see a few tornadoes.


Figure 3. Probability of more than 8 inches of snow falling, for the 24 hour period ending 7am EST Thursday January 27, 2011. Image credit: National Weather Service HPC.


Jeff Masters

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 384 - 334

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13Blog Index

A hallway or inner area...but too much glass in a bathroom....stay away from rooms, windows..ect...where there is glass or mirrows
Member Since: Posts: Comments:
KEEPER........Looks like it has picked up forward speed, That is the scariest line I have seen in years
Member Since: Posts: Comments:
382. IKE
Maybe the line is starting to weaken....


Member Since: Posts: Comments:
Member Since: July 15, 2006 Posts: 171 Comments: 53838
Quoting presslord:


Get out of the trailer...
lol
Member Since: Posts: Comments:
Quoting NRAamy:
if you don't have a storm cellar, how do you protect yourself from a tornado?

Amy.....They suggest that you go into the center off your house or a bathroom away from windows....A hallway is ideal, but no place can be guarenteed(hell, I can't spell)
Member Since: Posts: Comments:
Quoting FLWeatherFreak91:
I doubt there is much more potential for severe weather after the initial line passes though, as it should stabilize the atmosphere well.


The tail is usually the most intense part of the line.
Member Since: Posts: Comments:
Quoting NRAamy:
if you don't have a storm cellar, how do you protect yourself from a tornado?


Get out of the trailer...
Member Since: Posts: Comments:
Ah my power is flickering, I gotta go, torrential rain at 4 inches an hour and probably up to 50 mph
Member Since: August 21, 2008 Posts: 0 Comments: 7441
Possible Tornado near St Petersburg.
Member Since: Posts: Comments:
Quoting RitaEvac:
SW tail of line is still way out in Gulf, it'll deal with you later tonight, Keys and Miami gonna get theirs too
I doubt there is much more potential for severe weather after the initial line passes though, as it should stabilize the atmosphere well.
Member Since: December 1, 2006 Posts: 2 Comments: 3620
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE JACKSONVILLE FL
504 PM EST TUE JAN 25 2011

..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..

0445 PM FUNNEL CLOUD 3 NW ST. AUGUSTINE 29.92N 81.34W
01/25/2011 ST. JOHNS FL TRAINED SPOTTER

TWO MILES NORTH OF HWY 312 ST AUGUSTINE...FUNNEL CLOUD
REORTED


Member Since: Posts: Comments:
Across the northern part of St. Pete, an indicated tornado by radar!
Member Since: August 21, 2008 Posts: 0 Comments: 7441
if you don't have a storm cellar, how do you protect yourself from a tornado?
Member Since: Posts: Comments:
Tornado warning for my county now!
Member Since: August 21, 2008 Posts: 0 Comments: 7441
This will flood your car on the roadways folks

Member Since: July 14, 2008 Posts: 1 Comments: 9630
Tornado warning here with heavy rains and gusting winds. Keeping an eye on the gulls and pelicans on the dock in the hope they know more than I do.
Member Since: Posts: Comments:
SW tail of line is still way out in Gulf, it'll deal with you later tonight, Keys and Miami gonna get theirs too
Member Since: July 14, 2008 Posts: 1 Comments: 9630
RitaEvac......Great keeping up with the radar for us............Thanks
Member Since: Posts: Comments:
365. IKE

Member Since: Posts: Comments:
NWS should have another doppler radar in Ft Myers
Member Since: July 14, 2008 Posts: 1 Comments: 9630
Is there more out in the gulf behind what can be seen on tampa long range radar?? Satellite suggests there's going to be another line later tonight.
Member Since: December 1, 2006 Posts: 2 Comments: 3620
Finally a warning for Pinellas County, the rainfall rates are way underestimated, Ive had almost an inch in just the last 5 minutes, its blowing sideways, wild stuff!
Member Since: August 21, 2008 Posts: 0 Comments: 7441
Flooding rains
Member Since: July 14, 2008 Posts: 1 Comments: 9630
Member Since: July 14, 2008 Posts: 1 Comments: 9630
358. Kearn
doesn't it seem like the storms anywhere south of tampa are beginning to lose intensity??

it's very slight but noticable
Member Since: Posts: Comments:
Member Since: July 14, 2008 Posts: 1 Comments: 9630
Interesting weather here a few miles west of St Augustine.  Tornado warnings to the north and south.  No thunder/lightning at my house but torrential rain and gusty winds as the squall passes through.
Member Since: Posts: Comments:
Member Since: July 14, 2008 Posts: 1 Comments: 9630
That's a scary looking line......I'm hoping for the best...I guess I will get in around midnight
Member Since: Posts: Comments:
Deluge for Tampa
Member Since: July 14, 2008 Posts: 1 Comments: 9630
Member Since: July 14, 2008 Posts: 1 Comments: 9630
GOM IR Loop

Member Since: July 3, 2005 Posts: 424 Comments: 128284
THE NATIONAL WEATHER SERVICE IN JACKSONVILLE HAS ISSUED AN

* URBAN AND SMALL STREAM FLOOD ADVISORY FOR MINOR FLOODING OF POOR
DRAINAGE AREAS IN...
SOUTHERN PUTNAM COUNTY IN NORTHEAST FLORIDA...
THIS INCLUDES THE CITIES OF...POMONA PARK...PALATKA...
INTERLACHEN...
SOUTHEASTERN ALACHUA COUNTY IN NORTHERN FLORIDA...
THIS INCLUDES THE CITY OF MELROSE...
MARION COUNTY IN NORTHERN FLORIDA...
THIS INCLUDES THE CITIES OF...SALT SPRINGS...OCALA...LYNNE...
JUNIPER SPRINGS...FORT MCCOY...CITRA...

* UNTIL 615 PM EST

* AT 438 PM EST WEATHER SERVICE DOPPLER RADAR INDICATED A LINE OF
SHOWERS AND THUNDERSTORMS PRODUCING TORRENTIAL RAIN WITH RAINFALL
RATES OF 2 TO 3 INCHES PER HOUR. THE LINE STRETCHES FROM MELROSE TO
OCALA AND IS MOVING RAPIDLY EAST NORTHEAST AT APPROXIMATELY 40 MPH.
MOST OF THIS AREA HAS ALREADY PICKED UP 1 TO 2 INCHES OF RAIN TODAY.
ADDITIONAL RAINFALL AMOUNTS OF 1 TO 2 INCHES ARE POSSIBLE THROUGH
630 PM.

Happy to be on high ground in Melrose, FL :)
Member Since: July 18, 2005 Posts: 9 Comments: 4146
Oddly enough, local MET's are showing strong rotation to my west, but no warning? go figure, thunder has just picked way up again though...
Member Since: August 21, 2008 Posts: 0 Comments: 7441
Member Since: July 3, 2005 Posts: 424 Comments: 128284
SVR TSTM Warning now for me... I'm about 30 to 40 mi E of that line in Orange County...NWS is definitely giving people a pretty good heads up on what's coming.
Member Since: Posts: Comments:
looks like the cells have weakened a little off to my west, the thunder has died down, darn, I'm hoping for a nasty cell, just without the tornadoes, but no thunderstorm warnings have been issued.
Member Since: August 21, 2008 Posts: 0 Comments: 7441
083
WFUS52 KTBW 252145
TORTBW
FLC053-101-119-252215-
/O.NEW.KTBW.TO.W.0003.110125T2145Z-110125T2215Z/

BULLETIN - EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE TAMPA BAY AREA - RUSKIN FL
445 PM EST TUE JAN 25 2011

THE NATIONAL WEATHER SERVICE IN RUSKIN HAS ISSUED A

* TORNADO WARNING FOR...
SOUTHERN SUMTER COUNTY IN FLORIDA.
EASTERN HERNANDO COUNTY IN FLORIDA.
NORTHEASTERN PASCO COUNTY IN FLORIDA.

* UNTIL 515 PM EST

* AT 440 PM EST...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
TORNADO NEAR MASARYKTOWN...OR 7 MILES SOUTH OF BROOKSVILLE...MOVING
EAST AT 45 MPH.

* THE TORNADO WILL BE NEAR...
BROOKSVILLE.
DADE CITY NORTH.
RIDGE MANOR.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

IN ADDITION TO THE TORNADO...THIS STORM IS CAPABLE OF PRODUCING LARGE
HAIL AND WIDESPREAD DAMAGING WINDS.

IF YOU ARE IN THE PATH OF THE TORNADO GO TO A SMALL INTERIOR ROOM IN
A STRONG AND WELL CONSTRUCTED BUILDING. CARS AND MOBILE HOMES ARE NOT
SAFE. IF NO SHELTER IS AVAILABLE...LIE FLAT IN A DITCH OR CULVERT AND
COVER YOUR HEAD WITH YOUR HANDS.

TO REPORT SEVERE WEATHER TO THE NATIONAL WEATHER SERVICE PLEASE CALL
813-645-2323.

A TORNADO WATCH REMAINS IN EFFECT UNTIL 900 PM EST TUESDAY EVENING
FOR WESTERN FLORIDA.



LAT...LON 2857 8253 2875 8195 2840 8195 2834 8252
TIME...MOT...LOC 2145Z 260DEG 38KT 2848 8229




CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab FL Page Main Text Page
Member Since: July 3, 2005 Posts: 424 Comments: 128284
Member Since: July 15, 2006 Posts: 171 Comments: 53838
Member Since: July 3, 2005 Posts: 424 Comments: 128284
Member Since: July 3, 2005 Posts: 424 Comments: 128284
Member Since: July 15, 2006 Posts: 171 Comments: 53838
who the heck keeps hiding comments? whoever it is should stop. some people may be using this blog for real time alerts.
Member Since: January 3, 2009 Posts: 0 Comments: 46
I'm trying to figure out why warning haven't been issued for Pinellas and Hillsborough yet, they are very strong cells as well!
Member Since: August 21, 2008 Posts: 0 Comments: 7441

168
WFUS52 KJAX 252139
TORJAX
FLC109-252215-
/O.NEW.KJAX.TO.W.0004.110125T2139Z-110125T2215Z/

BULLETIN - EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE JACKSONVILLE FL
439 PM EST TUE JAN 25 2011

THE NATIONAL WEATHER SERVICE IN JACKSONVILLE HAS ISSUED A

* TORNADO WARNING FOR...
CENTRAL ST. JOHNS COUNTY IN NORTHEAST FLORIDA

* UNTIL 515 PM EST

* AT 439 PM EST...NATIONAL WEATHER SERVICE METEOROLOGISTS WERE
TRACKING A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO 9
MILES WEST OF SAINT AUGUSTINE SOUTH...OR 8 MILES NORTHEAST OF
HASTINGS...MOVING NORTHEAST AT 30 MPH.

* OTHER LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO SAINT
AUGUSTINE SOUTH...SAINT AUGUSTINE...VILANO BEACH...SOUTH PONTE
VEDRA BEACH AND GUANA RIVER STATE PARK.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

HEAVY RAINFALL MAY OBSCURE THIS TORNADO. TAKE COVER NOW! IF YOU WAIT
TO SEE OR HEAR IT COMING...IT MAY BE TOO LATE TO GET TO A SAFE PLACE.

SEEK SHELTER ON THE LOWEST FLOOR OF THE BUILDING IN AN INTERIOR
HALLWAY OR ROOM SUCH AS A CLOSET. USE BLANKETS OR PILLOWS TO COVER
YOUR BODY AND ALWAYS STAY AWAY FROM WINDOWS.

IF IN MOBILE HOMES OR VEHICLES...EVACUATE THEM AND GET INSIDE A
SUBSTANTIAL SHELTER. IF NO SHELTER IS AVAILABLE...LIE FLAT IN THE
NEAREST DITCH OR OTHER LOW SPOT AND COVER YOUR HEAD WITH YOUR HANDS.

REPORT SEVERE WEATHER OR DAMAGE TO THE NEAREST LAW ENFORCEMENT AGENCY
OR YOUR COUNTY EMERGENCY MANAGEMENT.

A TORNADO WATCH REMAINS IN EFFECT UNTIL 900 PM EST TUESDAY EVENING
FOR NORTHEASTERN FLORIDA.
Member Since: July 3, 2005 Posts: 424 Comments: 128284

Viewing: 384 - 334

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13Blog Index

Top of Page

About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

Local Weather

Mostly Cloudy
76 °F
Mostly Cloudy