Drought - May 2001


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U.S. Drought Highlights:

Contents Of This Report:

Click here to go to Top of Page National Overview

On the national scale,
  • severe drought affected about sixteen percent of the contiguous United States as of the end of May 2001;
  • the total drought area has held steady at about 7 to 15 percent for the last eight months (see graph below left);
  • the coverage of the current drought peaked in August 2000 at about 36% of the contiguous U.S., which was as extensive as the major droughts of the last 40 years, but not as large as the "dust bowl" droughts of the 1930's and 1950's;
  • on a broad scale, the last two decades were characterized by unusual wetness with short periods of extensive droughts, whereas the 1930's and 1950's were characterized by prolonged periods of extensive droughts with little wetness (see graph below right);
  • although different parts of the U.S. have experienced unusually wet conditions during the last 20 months, there continues to be little change in the overall national wetness picture;
  • the percentage of the nation severely wet has held steady at about five to ten percent during this period (see graph below left).
Click here for graphic showing U.S. Drought and Wet Spell Area, 1996-2001
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Click here for graphic showing U.S. Drought and Wet Spell Area, 1900-2001
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Although some areas of the U.S. had well above normal precipitation, many areas were very dry. May averaged near normal when precipitation is integrated across the nation. Eleven of the last 22 months have averaged well below the normal, while only two averaged well above normal (see graph to right). National 2001 precipitation ranks: Click here for graphic showing U.S. Precipitation Departure and Normals, January 1998-May 2001
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During May 2001, dry conditions returned to the Pacific Northwest and West regions, with the northwestern quarter of the country, from Montana to Nevada and northern California, suffering from long-term drought. May was the second dry month in a row for the Northeast and Southeast regions, while May rains brought relief to much of the Central region. This pattern is evident in: Two other drought-related monitoring tools are the Vegetation Health Index and the Keetch-Byram Drought Index:
  • NOAA satellite observations of vegetation health revealed increasing stress on vegetation in parts of the West and Southwest.
  • The Keetch-Byram Drought Index (KBDI) is used by the National Interagency Fire Center to monitor the risk of wildfires. The KBDI showed a drying trend along the Gulf and South Atlantic coasts and in parts of the West by the end of May. The Forest Service fire danger analysis indicated a continuing risk of wildfires in the western U.S., with the highest risk in the Southwest.

Click here to go to Top of Page Palmer Drought Indices

The Palmer Z Index shows how monthly moisture conditions depart from normal (short-term drought and wetness). May 2001 was severely dry across much of the country from Montana to Nevada, westward to the Pacific coast, across the Gulf coast and much of the Northeast, and over parts of Texas. Heavy rains brought drought relief to parts of the Ohio Valley. The animated maps to the right show the geographical pattern of the moisture anomalies for the last 12 months. On these maps, the red shading denotes dry conditions while the green shading indicates wet conditions. Click here for graphic showing U.S. Animated Palmer Z Index maps
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Click here for graphic showing U.S. Animated Palmer Drought Index maps
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The Palmer Drought Index maps show long-term (cumulative) meteorological drought and wet conditions. Long-term meteorological drought persisted across the Pacific Northwest, Gulf coast, and southern Appalachians, but decreased in intensity in the central Appalachians and in parts of the Ohio Valley and Northeast. The animated maps to the left show how the geographical pattern of the long-term (meteorological) moisture conditions has changed over the last 12 months. On these maps, the red shading denotes drought conditions while the green shading indicates wet conditions.

The Palmer Hydrological Drought Index maps show hydrological (long-term cumulative) drought and wet conditions, which more accurately reflect groundwater conditions, reservoir levels, etc. The PHDI indicates that hydrological drought persisted through the end of May across the Pacific Northwest states, northern and central Rockies, the Gulf Coast states, southern Appalachians, parts of the Ohio Valley, and over Maine and parts of Texas. The animated maps to the right show the geographical pattern of the long-term (hydrological) moisture anomalies for the last 12 months. On these maps, the red shading denotes dry conditions while the green shading indicates wet conditions. Click here for graphic showing U.S. Animated Palmer Hydrological Drought Index maps
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Click here to go to Top of Page Regional Drought Watch:

Click here to go to Top of Page Standardized Precipitation Index

The Standardized Precipitation Index (SPI) is another way of measuring drought. The index is negative for drought, and positive for wet conditions. The SPI is a probability index that considers only precipitation, while Palmer's indices, shown in the previous maps, are water balance indices that consider water supply (precipitation), demand (evapotranspiration) and loss (runoff).

The seven maps below show the May 2001 spatial patterns of SPI for seven different periods ranging from one month (short-term conditions) to 24 months (long-term conditions). When taken together, they give a combined geographical and temporal picture of the severity of precipitation anomalies. The maps illustrate, for example:

  • the core drought areas (much of the Northwest, parts of the Southeast and Northeast U.S., and extreme southern Texas) suffer from both short-term (1- to month-2) and long-term (9- to 2month-4) moisture deficits;
  • recent rains improved short-term (1- to month-2) conditions across much of the Ohio Valley, although longer-term (3- to 2month-4) dryness remains; and
  • much of the Southeast suffers from long-term (2month-4) drought.
Click here for graphic showing 1-Month SPI Map
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Click here for graphic showing 2-Month SPI Map
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Click here for graphic showing 3-Month SPI Map
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Click here for graphic showing 6-Month SPI Map
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Click here for graphic showing 9-Month SPI Map
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Click here for graphic showing 12-Month SPI Map
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Click here for graphic showing 24-Month SPI Map
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Click here to go to Top of Page Regional Overview

The following table shows the precipitation ranks for the nine standard U.S. regions for May 2001, the three-month period March-May 2001, and the twelve-month period June 2000-May 2001. A rank of 1 is driest and 107 (106 for June-May) is wettest.

Region May 2001 Mar-May 2001 Jun 2000-May 2001
Northeast 25 27 23
East North Central 100 102 102
Central 81 27 37
Southeast 42 63 21
West North Central 31 59 41
South 66 44 58
Southwest 76 78 73
Northwest 18 46 2
West 5 42 23

The map to the bottom left shows the departure from normal of the number of days with measurable precipitation for May 2001. The short-term dryness in the Northwest and parts of Florida, Alaska, and the Northeast shows up on this map as significant below-normal (brown) number of precipitation days. The above-normal precipitation along the Alaskan panhandle and from the upper Mississippi Valley to the central Appalachians is reflected in a preponderance of above-normal rain days.

The spring (March-May) departure from normal number of days with measureable precipitation is shown in the map to the bottom right. A similar wet/dry pattern is evident in Alaska with predominantly dry conditions in the Hawaiian stations. A below-normal number of rain days can be seen in the Northeast and from the northern Rockies to intermountain basin in the West. A mixed pattern appears from the Ohio Valley to the Gulf coast.

Click here for graphic showing Departure from Normal Number of Days with Measureable Precipitation Map, May 2001
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Click here for graphic showing Departure from Normal Number of Days with Measureable Precipitation Map, March-May 2001
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Click here to go to Top of Page Western U.S. Drought

May brought a return to drier-than-normal conditions over much of the Pacific Northwest after a wetter-than-normal April (see graph below left). Ranks for 2001:
  • 18th driest May,
  • 46th driest spring (March-May),
  • fifth driest January-May,
  • second driest month-12 period, June-May (see graph below right), second only to the record drought of 1976-77.
The Governors of Washington, Oregon, and Idaho have declared drought emergencies in their states. Mountain snowfall was below normal this past winter, with the snowpack already melted by early June from most western mountains, several weeks earlier than usual. Agriculture is suffering as irrigation puts additional strain on low reservoirs in Idaho and Washington.
Precipitation Ranks for the
Pacific Northwest, 2000-2001
Period Rank
Jun-May 2nd driest
Jul-May 2nd driest
Aug-May 2nd driest
Sep-May 4th driest
Oct-May 2nd driest
Nov-May 2nd driest
Dec-May 4th driest
Jan-May 5th driest
Feb-May 19th driest
Mar-May 46th driest
Apr-May 54th driest
May 18th driest
Click here for graphic showing Pacific Northwest Region Precipitation Anomalies, January 1998 - May 2001
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Click here for graphic showing Pacific Northwest Region Precipitation, June-May, 1895-2001
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Montana had the fifth driest May and third driest December-May on record in 2001. The dry conditions have contributed to falling well levels and to the development of scattered wildfires in parts of Montana and Idaho.
Click here for graphic showing West Region Precipitation Anomalies, January 1998 - May 2001
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The West region (California and Nevada) had the fifth driest May in 2001. The effects from the lack of rain were compounded by higher than normal evaporation as the region experienced its hottest May in the 107-year record. Additional ranks for this year's rainy season:
  • 17th driest November-February,
  • 16th driest November-March,
  • 24th driest October-May,
  • 23rd driest June-May.


Click here to go to Top of Page Southeast and Southern Plains Drought

The Southeast region has experienced dry conditions over much of the last four years (since May 1998, see graph below left). Although some parts of the region have seen recent drought relief, long-term drought continued region-wide. May 2001 marked the second dry month in a row, following an unusually wet March. For the Southeast region,
  • 14 of the last 19 months averaged below to much below normal (see graph below left),
  • 21st driest June-May on record (see graph below right),
  • 23rd driest December-May on record,
  • 26th driest January-May on record,
  • 42nd driest May on record,
  • third consecutive year with below-average June-May precipitation,
  • tenth consecutive year with below-average May precipitation.

Click here for graphic showing Southeast Region Precipitation Anomalies, January 1998 - May 2001
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Click here for graphic showing Southeast Region Precipitation, June-May, 1895-2001
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Very dry conditions continued in Florida during May. Highlights in the state include:
  • the seventh driest October-May,
  • the ninth driest April-May and June-May,
  • the 25th driest May,
  • third driest May-April on record,
  • Lake Okeechobee, the back-up reservoir for Florida’s heavily populated east coast, dropped to 9 feet above sea level – the lowest on record,
  • wildfires continued to pose a hazard to travelers and residents, with perhaps the state's largest ever observed wildfire occurring in the Mallory Swamp near Mayo,
  • since January 1st, more than 3100 wildfires have charred 135,700 hectares (335,300 acres) in the state.
The South region had the 42nd wettest May on record in 2001. However, parts of the southern Plains continued in prolonged drought. Western and southern Texas were in the moderate to severe drought category by the end of May.


Click here to go to Top of Page Northeast Region Dryness

Much of the Northeast region experienced the second dry month in a row during May 2001 (see graph below left): The dry spell lasted generally from late April through mid-May in most parts of the region. Rainfall during the last half of May brought area reservoirs and streamflow back to normal or above normal.
Click here for graphic showing Northeast Region Precipitation Anomalies, January 1998 - May 2001
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Click here for graphic showing Northeast Region Precipitation, April-May, 1895-2001
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Click here to go to Top of Page Additional Contacts:

Damage due to the drought has been summarized by NOAA and the Office of Global Programs in the Climatological Impacts section of the Climate Information Project. Crop impact information can be found at the USDA NASS (National Agricultural Statistics Service) and Weekly Weather and Crop Bulletin pages. Drought statements by local National Weather Service Offices can be found at the NWS Hydrologic Information Center. Drought threat assessments and other information can be found at NOAA's Drought Information Center. Additional drought information can be found at the National Drought Mitigation Center, the USDA's National Agricultural Library, the interim National Drought Council, and the NOAA Paleoclimatology Program. The following states have set up web pages detailing their plans to handle drought emergencies:
Florida Panhandle - Georgia - Hawaii - Idaho - Kentucky - Montana - Nebraska
New Mexico - North Carolina - Oklahoma - South Carolina - Texas - Washington

For additional information on the 2001 wildfire season please see the National Interagency Fire Center web site or the U.S. Forest Service Fire and Aviation web site.

Additional climate monitoring graphics can be found at the Climate Prediction Center's monitoring pages:

Citing This Report

NOAA National Climatic Data Center, State of the Climate: Drought for May 2001, published online June 2001, retrieved on November 28, 2014 from http://www.ncdc.noaa.gov/sotc/drought/2001/5.