Drought - August 2002
U.S. Drought Highlights:
- On the national scale, severe to extreme drought affected about 33 percent of the contiguous United States as of the end of August 2002
- moderate to extreme drought affected about 48 percent of the contiguous U.S.
- Most of the western U.S. continued to suffer from drought, both short-term and long-term
- Conditions continued very dry over parts of the adjoining Great Plains
- August was dry across much of the eastern U.S. into the Ohio Valley, with parts of the Southeast suffering from severe long-term drought
Please Note: The data presented in this drought report are preliminary. Ranks, anomalies, and percent areas may change as more complete data are received and processed.
On the national scale,
- about 48 percent of the contiguous U.S. fell in the moderate to extreme drought categories (based on the Palmer Drought Index) at the end of August;
- severe drought affected about 33 percent of the contiguous United States as of the end of August 2002, which is a decrease from the 37 percent coverage at the end of July;
- the coverage of the current (November 1999-present) national-scale drought first 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 1930s and 1950s;
- the total drought area decreased to about 10 percent by November 2000, but has shown a general increasing trend for much of the period since then, reaching in June 2002 the peak it had first reached in August 2000;
- on a broad scale, the last two decades were characterized by unusual wetness with short periods of extensive droughts, whereas the 1930s and 1950s were characterized by prolonged periods of extensive droughts with little wetness;
- although various parts of the U.S. have experienced unusually wet conditions during the last 34 months, little change occurred in the aggregate national wetness picture during much of this period;
- the percentage of the nation severely wet has remained below about eleven percent during this period, reaching about 6 percent by the end of August 2002;
- a file containing the national monthly percent area severely dry and wet from 1900 to present is available;
- historical temperature, precipitation, and Palmer drought data from 1895 to present for climate divisions, states, and regions in the contiguous U.S. are available at the Climate Division: Temperature-Precipitation-Drought Data page in files having names that start with "drd964x" and ending with "txt" (without the quotes).
August brought beneficial rains to some of the regions that have been experiencing severe drought, especially along the coastal Southeast and parts of the central Plains. But dry conditions continued across much of the drought area, from the Northeast to the Ohio Valley and southern Appalachians, and across much of the West. Unusually hot conditions accompanied the dryness, especially from the Northeast to Ohio Valley, but also from the Southwest and into parts of the Great Plains. August was dry at most of the primary stations in Hawaii and Puerto Rico. Alaska was dry in the western and northern sections but wet in the southeast.
These overall conditions are evident in the following indicators:
- the runoff, evaporation, and soil moisture conditions as calculated by the National Weather Service,
- maps showing the percent of normal precipitation for airport stations for August and summer (June-August),
- the percent of average precipitation map for the hydrologic year (October 1, 2001 - September 30, 2002) for the SNOTEL stations in the western mountains provided by the USDA Water and Climate Center,
- the statewide precipitation ranks for current month (short-term) and 3-months, 6-months, and 12 months (longer-term),
- the short-term surface wetness anomaly map for August computed by the National Climatic Data Center from the Special Sensor Microwave Imager (SSMI), a polar orbiting satellite with global coverage, and
- the USGS November daily streamflow maps.
Two other drought-related monitoring tools are the Vegetation Health Index and the Keetch-Byram Drought Index:
- NOAA satellite observations of vegetation health from early September revealed stress on vegetation across the southwestern into the central Plains, and across parts of the Midwest to Great Lakes.
- The USDA Forest Service uses a satellite-based vegetation health index tool to monitor the risk of wildfires. This Greenness Index for late August revealed above-average stress on vegetation across much of the the West and adjoining Great Plains, as well as parts of the eastern U.S. and Ohio Valley.
- The Keetch-Byram Drought Index (KBDI) is used by the Wildland Fire Assessment System to monitor the risk of wildfires. The end-of-August KBDI showed dry conditions across parts of the West, central, and souther Plains, Ohio Valley, and much of the eastern U.S. The Forest Service fire danger analysis indicated a high risk of wildfires across parts of the western U.S into the central Plains, and across part of Maine. The fire threat conditions can change rapidly from week to week.
The rainfall and surface wetness patterns averaged across the summer months (June-August) clearly indicate the areas suffering from moisture stress during this season. The greatest wetness deficiency occurred in the central Plains and Southeast states, with deficiencies developing in the Ohio Valley. Below-normal rainfall occurred at stations in those areas as well as along most of the east coast and much of the Far West, Puerto Rico, and the Hawaiian Islands. States having summer precipitation ranks of tenth driest, or drier, were located in the southwestern U.S. and Ohio Valley.
Western U.S. Drought
August is in the dry season for much of the West and Northwest regions, so below normal summer precipitation has less of an impact here than in the winter. However, this month is in the middle of the wet season for the Southwest region and the northern Rockies. On a regional basis, August 2002 was drier than normal across these western areas. The combination of subnormal rainfall and, in some areas, hot temperatures resulted in widespread severe to extreme short-term drought. Summer (June-August) 2002 was drier than normal in these three regions, with the West region having the driest summer on record. The cumulative effect of the dryness over the last several months in the Southwest has resulted in record dry seasons from May-August back to September-August. Severe to extreme long-term drought was widespread across the western U.S. Water year (October 2001-present) precipitation totals were above average in the Northwest reflecting a rainy wet season earlier, but totals dropped precipitously toward the Rockies and the Southwest.
By the beginning of September, topsoil moisture conditions were extremely dry across much of the western U.S. According to September 1 USDA reports, 70% or more of the topsoil was short to very short in Wyoming (91%), Utah (90%), Oregon (89%), New Mexico (85%), and Idaho (71%).
Range and pasture conditions continued to deteriorate in many areas during August. According to September 1 USDA reports, conditions on 49% of the nation's pastures and rangeland were poor or very poor (compared to 37% at this time last year):
- 80% or more of the range and pasture lands were reported in poor to very poor condition in Colorado (93%), California (90%), Arizona (83%), and Wyoming (80%),
- 50% or more poor to very poor in Utah (73%), New Mexico (70%), Oregon (63%), Washington (51%), and Nevada (50%).
A detailed review of drought conditions is available for the following regions and states:
- Pacific Northwest region
- West region
- Southwest region
- New Mexico
Central U.S. Drought
The rainfall pattern between the Rocky and Appalachian mountain ranges was mixed during August. Abundant rains fell from northeast Montana to the western Great Lakes, resulting in a wetter-than-normal month for the West North Central and East North Central regions. The rains brought short-term drought relief to parts of the Dakotas and Nebraska, but long-term conditions continued very dry.
Meanwhile, August marked the third consecutive dry month for much of the Ohio Valley, resulting in the 18th driest summer for the Central region. August was rainy over parts of the South region, except for the drought areas of the Trans Pecos and deep south Texas, which continued very dry.
By the beginning of September, topsoil moisture conditions were extremely dry across much of the central U.S. According to September 1 USDA reports:
- 70% or more of the topsoil was short to very short in Ohio (84%), West Virginia (79%), Kansas (73%), Nebraska (71%), Illinois (71%), and Kentucky (71%), and
- 50% or more short to very short in Missouri (65%).
- 80% or more of the range and pasture lands were reported in poor to very poor condition in Nebraska (86%),
- 75% or more poor to very poor in Kansas (73%), and
- 50% or more poor to very poor in Ohio (68%), Indiana (67%), South Dakota (60%), North Dakota (56%), Montana (54%), and Missouri (51%).
A detailed discussion of drought conditions is available for the following regions and states:
Eastern U.S. Drought
This month continued a dry pattern for the Northeast region, giving it the third driest July-August on record. Parts of the Southeast were wet during August while other parts continued very dry, resulting in a regionwide average that was near normal. This month marked the eleventh consecutive month with slightly to much below normal precipitation averaged across the Southeast.
By the beginning of September, topsoil moisture conditions were extremely dry across much of the eastern U.S. According to September 1 USDA reports:
- 70% or more of the topsoil was short to very short in Maine (96%), Rhode Island (91%), Pennsylvania (90%), and Virginia (77%), and
- 50% or more short to very short in New Hampshire (61%), Georgia (60%), Connecticut (56%), Vermont (54%), New York (52%), and Maryland (50%).
- 80% or more of the range and pasture lands were reported in poor to very poor condition in Maine (81%),
- 75% or more poor to very poor in Pennsylvania (84%) and New Jersey (79%), and
- 50% or more poor to very poor in Virginia (69%), Maryland (65%), Delaware (63%), North Carolina (62%), Massachusetts (51%), and Rhode Island (50%).
Severe to extreme long-term drought persisted from Long Island and southern Pennsylvania to western Georgia. The long-term deficits were so severe that two states (North Carolina and Virginia) had the driest September-August in the 108-year record, with several others second driest (see map below right). The severe short-term dryness in Maine gave the state the driest August on record.
A detailed discussion of drought conditions is available for the following regions and states:
- Southeast region
- North Carolina
- South Carolina
- Northeast region
- New Jersey