Drought - April 2001


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U.S. Drought Highlights:

Contents Of This Section:

Top of Page National Overview

On the national scale,
  • severe drought affected about seven percent of the contiguous United States as of the end of April 2001;
  • the total drought area has held steady at about 7 to 15 percent for the last seven 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 19 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).
 graphic showing U.S. Drought and Wet Spell Area, 1996-2001
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 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. April was a dry month when precipitation is integrated across the nation. Eleven of the last 21 months have averaged well below the normal, while only two averaged well above normal (see graph to right). National 2001 precipitation ranks:  graphic showing U.S. Precipitation Departure and Normals, January 1998-April 2001
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During April 2001, the U.S. Pacific Northwest continued to suffer from drought in spite of a wetter-than-normal month. Dry conditions returned to the southern Plains and the Northeast, and April marked the second dry month in a row for the Ohio Valley. 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.
  • 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 with an increasing threat of wildfires across Florida and in parts of the West by the end of April. The Forest Service fire danger analysis indicated a continuing risk of wildfires in the Southwestern U.S. and an increasing threat of wildfires in the northern High Plains and the southern Great Lakes.

Top of Page Palmer Drought Indices

The Palmer Z Index shows how monthly moisture conditions depart from normal (short-term drought and wetness). April 2001 was severely dry across much of the country from the Northeast to Texas and Florida. Moist conditions during April brought temporary relief from the drought to the Pacific Northwest. Heavy rains from the central Plains to the northern Great Lakes contributed to flooding of the upper Mississippi River. 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.  graphic showing U.S. Animated Palmer Z Index maps
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 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 and intensified across Florida and from the southern Appalachians to Ohio Valley. 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 April across the Pacific Northwest states, and hydrologic conditions deteriorated across parts of the Southeast, Ohio Valley, and Northeast. 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.  graphic showing U.S. Animated Palmer Hydrological Drought Index maps
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Top of Page Regional Drought Watch:

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 April 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:

  • short-term (1-month) dryness affected the Northeast, coastal Mid-Atlantic, Southeast, and southern Plains states but above-normal precipitation in March resulted in a neutral (mid-range) SPI in these regions for the 2-month period;
  • short-term (2-month) dryness was centered in the Ohio Valley and spread northward to the Great Lakes and south and westward to Tennessee and Oklahoma. The lack of precipitation was exacerbated by unusually warm April temperatures in this region;
  • March and April rains brought short-term relief to the Pacific Northwest, but longer-term (3-month to 24-month) drought still affects much of the Pacific Northwest and northern Rockies; and
  • the Southeast, Ohio Valley, and parts of the Northeast suffer from long-term drought.
 graphic showing 1-Month SPI Map
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 graphic showing 2-Month SPI Map
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 graphic showing 3-Month SPI Map
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 graphic showing 6-Month SPI Map
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 graphic showing 9-Month SPI Map
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 graphic showing 12-Month SPI Map
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 graphic showing 24-Month SPI Map
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Top of Page Regional Overview

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

Region April 2001 Feb-Apr 2001 May 2000-
Apr 2001
Northeast 3 28 40
East North Central 106 95 87
Central 20 19 29
Southeast 9 40 9
West North Central 98 93 52
South 4 58 48
Southwest 79 81 64
Northwest 89 26 3
West 85 66 29

The map to the right shows the departure from normal of the number of days with measurable precipitation for April 2001. The short-term dryness in the Northeast, Southeast, and southern Plains shows up on this map as significant below-normal (brown) number of precipitation days. The above-normal precipitation in the West and Northwest regions is reflected in a preponderance of above-normal rain days. The rain day anomaly pattern was mixed in Alaska and Hawaii.  graphic showing Departure from Normal Number of Days with Measureable Precipitation Map, April 2001
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Top of Page Western U.S. Drought

April brought above-normal precipitation to much of the Pacific Northwest. This was a welcomed change from the unusually dry conditions that characterized much of the previous five months (see graph below left). Ranks for 2001: The Governors of Washington, Oregon, and Idaho declared drought emergencies in their states. The extreme dryness of this year's rainy season caused the statewide Palmer Drought Index in Oregon to rapidly decrease, reaching its most severe level since 1977.

The well below normal reservoir levels and mountain snowpack are having a major impact on water supplies. Severe agricultural impacts have been noted in parts of Oregon and northern California. A potentially severe wildfire season is of concern to those in the Pacific Northwest.

Precipitation Ranks for the
Pacific Northwest, 2000-2001
Period Rank
May-Apr 3rd driest
Jun-Apr 2nd driest
Jul-Apr 2nd driest
Aug-Apr 3rd driest
Sep-Apr 3rd driest
Oct-Apr 3rd driest
Nov-Apr 2nd driest
Dec-Apr 3rd driest
Jan-Apr 6th driest
Feb-Apr 26th driest
Mar-Apr 40th wettest
(68th driest)
Apr 19th wettest
(89th driest)
 graphic showing Pacific Northwest Region Precipitation Anomalies, January 1998 - April 2001
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 graphic showing Pacific Northwest Region Precipitation, November-April, 1895-2001
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Parts of the northern Rockies and northern High Plains have experienced dry conditions. For example, Montana had below-average surface wetness and soil moisture in April. Long-term dry conditions have resulted in the 13th driest May-April on record with the statewide Palmer Drought Index dropping to the lowest levels since the drought of the late 1980's.
 graphic showing West Region Precipitation Anomalies, January 1998 - April 2001
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The West region (California and Nevada) had a wet April. The 2000-2001 rainy season started out dry (see graph to left), but rains during the last half helped replenish reservoirs and add to the mountain snowpack. The severity of the dryness at the start of the season, however, resulted in the 29th driest May-April on record.


Top of Page Southeast and Southern Plains Drought

April was dry for much of the Southeast and southern Plains regions (see graphs below). Although some parts of the Southeast have seen recent drought relief, long-term drought continued region-wide. The hardest-hit areas have had moisture deficits for the last three years, tracing the drought to the onset of La Niña conditions in early 1998. For the Southeast region,
  • nine of the last 12 months averaged below to much below normal (see graph below left),
  • ninth driest May-April on record,
  • third consecutive year with below-average May-April precipitation,
  • short-term (April) precipitation across the region was variable from state to state,
  • on the long-term (May-April) the region was predominantly dry,
  • the southern Appalachian Mountains of western North Carolina have suffered from persistent drought for the last three years.

Conditions in Florida were especially severe:

  • April saw a return to dry conditions following a short reprieve in March,
  • statewide Palmer Index continued in the severe drought category,
  • third driest May-April on record,
  • third consecutive May-April with below-average rainfall,
  • wildfires closed major highways in southern Florida,
  • since January 1st, more than 2200 wildfires have charred 178,138 acres in the state.
Statewide Precipitation Ranks for Florida, 2000-2001
Period Rank
May-Apr 3rd driest
Jun-Apr 12th driest
Jul-Apr 14th driest
Aug-Apr 20th driest
Sep-Apr 26th driest
Oct-Apr 9th driest
Nov-Apr 22nd driest
Dec-Apr 20th driest
Jan-Apr 29th driest
Feb-Apr 36th driest
Mar-Apr 39th wettest
Apr 7th driest
 graphic showing Southeast Region Precipitation Anomalies, January 1998 - April 2001
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 graphic showing South Region Precipitation Anomalies, January 1998 - April 2001
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April 2001 ranked as the fourth driest April on record for the southern Plains. This is a departure from the last three months, which were wetter than normal (see graph above right). When the unusual wetness of October 2000-March 2001 is combined with the dryness of April this year and last summer, the precipitation ranks fall in the mid-range (see regional overview table above).


Top of Page Central Region Dryness

April marked the second month in a row with much below normal precipitation averaged across the Central region (see graph below left). Ranks for 2001:
  • 20th driest April,
  • tenth driest March,
  • seventh driest March-April in the 1895-2001 record (see graph below right),
  • six of the last seven months have been drier than normal, resulting in the ninth driest October-April.
This year marks the second consecutive year with below normal precipitation during these periods.
 graphic showing Central Region Precipitation Anomalies, January 1998 - April 2001
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 graphic showing Central Region Precipitation, March-April, 1895-2001
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Top of Page Northeast Region Dryness

April 2001 was the third driest April on record in the Northeast region (see graph below right) and marked a return to the predominantly dry conditions which have characterized the region during much of the last seven months (see graph below left). October 2000-April 2001 ranked as the ninth driest such period in the 1895-2001 record, but when the unusual wetness of late spring and early summer 2000 is factored in, the last 12 months ranked as only the 40th driest May-April.

The heavy snow cover at the beginning of the month rapidly melted and was nearly gone by late April. Unusually warm temperatures during late April and early May increased the threat of fire danger to parts of the region, especially Maine, which had the driest April and seventh driest February-April.

 graphic showing Northeast Region Precipitation Anomalies, January 1998 - April 2001
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 graphic showing Northeast Region Precipitation, April, 1895-2001
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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 April 2001, published online May 2001, retrieved on July 28, 2014 from http://www.ncdc.noaa.gov/sotc/drought/2001/4.