Drought - Annual 2010
The data presented in this drought report are preliminary. Ranks, anomalies, and percent areas may change as more complete data are received and processed.
Contents Of This Report:
National Drought Overview
On a month-by-month basis, 2010 was characterized by large areas of warm and wet weather. While about a fifth or more of the country experienced very cold (at the tenth percentile of the historical record or colder) monthly temperature anomalies during February, May, and December, warm temperature anomalies were more prevalent. Large areas of the country (15 percent or more) had very warm (at the tenth percentile of the historical record or warmer) temperature anomalies for many more months (each month from March through September, as well as December), including about a third or more during April, June, and August. The unusual and persistent warmth, especially during the growing season, increased evaporation and intensified local drought conditions. About a tenth or more of the country was very dry (at the tenth percentile of the historical record or drier) during five months (March, April, September, October, and December). Based on early analysis of data, March 2010 ranked as the 35th driest March, nationally, in the 1895-2010 record, April ranked 36th driest, and October 39th driest. The dryness, however, was counterbalanced by very wet (monthly precipitation totals at the 90th percentile of the historical record or wetter) conditions over a tenth or more of the country during several more months (January, September, October, December, and each month from April through July). On a national scale, May was 22nd wettest, June ranked 11th wettest, and July 6th wettest.
The year started out with drought in the West and small parts of the southern Plains and Great Lakes. During the spring (March-May), drought developed in parts of the South and intensified in the western Great Lakes. Drought conditions contracted in the West and western Great Lakes, but intensified in the Southeast and mid-Atlantic states, during the summer (June-August). By October, moderate to extreme drought had developed in the South and had spread into the Ohio Valley. Drought relief occurred in the Ohio Valley with heavy rains at the end of November. Much of Hawaii suffered through a prolonged dry spell for most of the year, but heavy rains brought limited relief in December.
The percent area* of the contiguous U.S. experiencing moderate to extreme drought started the year at about 4 percent, hovered between 5 and 10 percent through the summer, then expanded to about 16 percent by December. According to U.S. Drought Monitor (USDM) statistics, the percent of the U.S. (including Alaska, Hawaii, and Puerto Rico) experiencing moderate (D1) to exceptional (D4) drought was about 11 percent at the beginning of the year, contracted to about 6.6 percent at the end of winter and again in mid-summer, and ended the year at around 20 percent. The mid-summer minimum represents the smallest percent area in moderate to exceptional drought for the U.S. during the 10-year history of the USDM.
*This drought statistic is based on the Palmer Drought Index, a widely used measure of drought. The Palmer Drought Index uses numerical values derived from weather and climate data to classify moisture conditions throughout the contiguous United States and includes drought categories on a scale from mild to moderate, severe and extreme.
Regional Drought Overview
The drought epicenters during 2010 were the western Great Lakes, much of the Southeast, the Ohio Valley, the mid-Atlantic states, Hawaii, and parts of the West. Low stream (April, May, September, October), reservoir and stock pond levels, and depleted soil moisture (July 4, August 1, September 5, September 26, October 31) combined with hot temperatures (spring, summer, September) and high evaporation to ravage agricultural (pasture, range and crop) lands as the growing season progressed. As noted by the U.S. Department of Agriculture (USDA), severe agricultural impacts were felt in the mid-Atlantic states by mid summer and into the South and Ohio Valley by early to mid fall. Satellite observations of vegetative health indicated that vegetation in the West was stressed in the spring but improved by early fall. The reverse situation occurred from the Ohio Valley to Gulf and Atlantic coasts, where conditions deteriorated from summer to fall.
Drought lingered in the western Great Lakes, primarily in northern Wisconsin and the Upper Peninsula of Michigan, at the beginning of the year. Below-normal precipitation during the winter and spring significantly dried the soils. March-May 2010 was record dry in Michigan's Upper Peninsula (climate division 1, climate division 2). Beneficial precipitation beginning in June significantly reduced the drought by the end of summer.
A moderate El Niño brought beneficial rain and snow to parts of the West during the 2009-2010 wet season. Above-normal precipitation continued during the summer and fall months. Drought conditions improved from 32 percent moderate to exceptional drought coverage at the beginning of the year to about 6 percent by the end of November, but the coverage increased to about 12 percent (USDM statistics) by year's end as drought increased in the Southwest. Based on Palmer Drought Index statistics (which go back to 1900), moderate to extreme drought coverage decreased from about 28 percent at the beginning of the year (March peak) to about 4 percent by the end of the year. The 2010 decrease is similar to the low drought interlude that occurred in 2005. Most of the last ten years have been characterized by persistent drought over the West, making it one of the most pronounced drought decades of the last 110 years.
Dry conditions developed in the Southeast during the spring and summer, especially in the Lower Mississippi Valley. Parts of northern Louisiana and adjacent Arkansas and Mississippi had near-record dry conditions for January-September (Louisiana climate division 3). The summer dryness was accompanied by record hot temperatures, which increased evaporation and magnified the drought impacts. The dryness continued in various parts of the South during the next four months (September, October, November, December), with 2010 ranking as the driest year on record for parts of the Lower Mississippi Valley (Louisiana climate divisions 2, 3, and 4, Mississippi climate division 4, and Arkansas climate division 8). By late summer to early fall, severe hydrological and agricultural impacts were felt in the region. Agricultural impacts decreased as the growing season ended, but by the end of December, half of the Southeast and two-thirds of the South were classified in moderate to extreme drought.
Drought crept into the mid-Atlantic states during the summer as hot and dry weather dominated the region. Hydrological and agricultural impacts were felt as soils dried. Drought conditions peaked the week before September ended. Heavy rains during the last two days of September and beginning of October, from the remnants of Tropical Storm Nicole, brought significant relief and an abrupt end to the drought across much of the Eastern Seaboard.
Dry conditions had developed in parts of the Ohio Valley by the end of summer and intensified and spread during September and October, resulting in significant agricultural impacts. South Central Indiana (climate division 8) had the second driest August-October on record. Beneficial frontal rains at the end of November resulted in significant improvement, but areas of drought remained (USDM from December 28 versus November 23).
Moderate (D1) to exceptional (D4) drought afflicted much (nearly half or more) of Hawaii throughout 2010 (see animation to right). About three-fourths or more of the state was in the D1-D4 category in February, June, and September, and at several points during the year almost all of the state experienced abnormally dry (D0) to exceptional drought (D4) conditions. Very dry to near-record dry conditions occurred during the summer and for 12-month, 24-month, and 36-month periods at several stations (Hilo, Honolulu, Kahului, and Lihue). Significant agricultural and hydrological impacts occurred during this year's drought, which is the worst drought episode of the decade. Beneficial rains during December reduced the drought coverage, but by the end of the year a third of Hawaii was still experiencing moderate to extreme drought.
A small area of moderate drought (D1) appeared on the USDM map for Alaska at mid-summer. Otherwise, the state experienced only abnormally dry (D0) conditions throughout the year, peaking at just under half of the state in June. Other than a small area of D0 the first week of the year, Puerto Rico has remained free of drought or abnormally dry conditions on the USDM throughout the year.
Tree ring records provide a useful paleoclimatic index that extends our historical perspective of droughts centuries beyond the approximately 100-year instrumental record. Several paleoclimatic studies have shown that droughts as severe as, or worse, both in magnitude and duration, than the major 20th century droughts have occurred in the U.S. during the last thousand years. The following paleodrought report was prepared by the NOAA/NCDC Paleoclimatology and Climate Monitoring branches during 2010:
Did You Know?
Drought in the Colorado River Basin
The decade-long drought in the West has had a severe impact on the water level of Lake Mead. By the end of October 2010, data from the U.S. Department of the Interior Bureau of Reclamation indicated that the level of Lake Mead had dropped to 1082.36 feet, which is the lowest level since the lake was filled in the 1930s. The previous lowest level was 1083.57 feet, reached in March 1956 during the peak of the 1950s drought. This has serious implications for water supplies in Arizona and Nevada.
Lake Mead is one of several reservoirs along the Colorado River. A major water source for the Colorado River is precipitation that falls in the central Rocky Mountains of Colorado, Wyoming, and Utah. This region is the Upper Colorado River Basin. Much of the West has experienced very dry conditions for the last ten years. This decade of drought is reflected in the precipitation received in the Upper Colorado River Basin. The early 2000s were very dry, with the Upper Colorado's Palmer Hydrological Drought Index (PHDI) reaching record low levels during the summer of 2002.
Droughts in the West, including in the Upper Colorado Basin, have been getting more widespread and severe during the last 50 to 90 years of instrument-based weather records (large-scale U.S. weather records go back to 1895). Tree ring records provide a useful paleoclimatic index that extends our historical perspective of droughts centuries beyond the approximately 100-year instrumental record. A 2129-year paleoclimatic reconstruction of precipitation for northwest New Mexico indicates that, during the last 2000 years, there have been many droughts more severe and longer-lasting than the droughts of the last 110 years. This has implications for water management in the West. For example, the Colorado Compact is the legal agreement used for allocation of Colorado River waters among the western states. The Compact was negotiated early in the 20th century during a very wet period, which was not representative of the long-term climatic conditions of the West.
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