NCDC / Climate Monitoring / Climate of 2007 / Annual / Drought / Help
Climate of 2007 Annual Review U.S. Drought
National Climatic Data Center, 15 January 2008
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The data presented in this drought
report are preliminary. Ranks, anomalies, and percent areas may change
as more complete data are received and processed.
National Drought Overview
Dry conditions predominated during much of the year across large parts of the Southeast, West, and Upper Great Lakes. March, May, August, and November were especially dry over large areas. Increased evaporation from anomalously warm temperatures combined with the lack of precipitation to exacerbate the drought conditions, especially during the summer months. A new core dry area developed over the mid-Atlantic states during the summer and fall. Unusually wet conditions in the southern and central Plains and into the Lower Great Lakes by late summer and early fall kept the three main drought areas (West, Southeast, Upper Great Lakes) separated. The January 1, 2008 U.S. Drought Monitor depicts conditions at the end of 2007.
Several short-lived dry episodes occurred in other regions throughout
the year, notably in the Ohio Valley and Northeast in May and the northern Plains in July.
The percent area* of the contiguous U.S. experiencing moderate to extreme drought grew steadily from 16 percent in January to a peak of about 42 percent by August, declined during the next 2 months, expanded again in November, and declined again in December.
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*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.
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The most extensive
national drought coverage during the past 110 years (the period of
widespread reliable instrumental records) occurred in July 1934 when 80 percent
of the contiguous U.S. was in moderate to extreme drought. Although the
current drought and others of the 20th century have been widespread and
of lengthy duration, tree ring records indicate that the severity of
these droughts was likely surpassed by other droughts including that of
the 1570s and 1580s over much of the western U.S. and northern Mexico.
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Regional Drought Overview
Impacts from this year's drought were felt especially hard by the agricultural and hydrological communities. Low streams, reservoirs, and stock ponds and depleted soil moisture ravaged pastures, rangeland, and cropland as the growing season progressed. Very dry soil moisture conditions stretched from coast to coast at the beginning of August, but improved in the Great Lakes and northern Plains by month's end. Agricultural conditions were especially harsh in the West and Great Lakes to Southeast at the end of July when many states had more than half of their pasture and rangeland in poor to very poor condition. Unusually hot temperatures in the West during July exacerbated the drought conditions. The heat spread into the Southeast during August. By the end of September, pasture and rangeland conditions improved in the Great Lakes region after beneficial rains but worsened in the Southeast. |
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The governors of several states implemented water conservation measures or declared drought disasters or states of emergency. These include Alabama, Florida, and Georgia in the Southeast, and California and Oregon in the West, during May. In July, the governors of Maryland and Tennessee made similar declarations for part or all of their states. In September and October the list expanded to include Connecticut, Delaware, and North Carolina.
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Parts of the Southeast have been dry since December 2006. This dryness has been associated with a strong subtropical Bermuda High which stretched across the North Atlantic into the Southeast, deflecting tropical storm systems away from the region for much of the spring and summer. A strengthening La Niña during the last half of the year compounded the dryness. Regionwide, every month in 2007, with the exception of October and December, averaged drier than normal. This persistent lack of precipitation has resulted in a record dry March-May and December-September for the region.
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Several southeastern states had record or near-record dryness during 2007. Especially dry periods include: February-April, February-May, March-May, January-June, and March-August. The drought depleted soil moisture, dessicated vegetation, shrank rivers, and dried up wells. Many communities implemented water restrictions as municipal water supplies dwindled. Wildfires plagued Florida during March and April, and Lake Okeechobee's level fell to 8.94 feet by the end of May, breaking the record low of 8.97 feet set back in May 2001. Alabama Power, the state's largest utility, operated some of its coal plants at significantly reduced levels by summer to avoid raising water temperatures in the Coosa, Black Warrior and Mobile rivers. The Tennessee Valley Authority shut down Brown's Ferry Number 2 nuclear power plant in August due to inadequate streamflow needed to cool the reactor.
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In the Lake Superior drainage area (Upper Michigan, northern Wisconsin, and northeast Minnesota), May-August was persistently dry and most of the previous 12 months were very dry (May-August, September-August). The late spring to early fall period is normally the wettest season for this region. Unusually dry conditions during this season for the last several years resulted in a record low level for Lake Superior, which impacted shipping and recreational activities. The average Lake Superior water level at the end of August 2007 was 600.4 feet above mean sea level, a foot lower than a year earlier and two inches lower than the previous record of 600.5 feet in 1926. In September, the level dipped 1.6 inches beneath the previous low for that month reached in 1926, according to NOAA's Great Lakes Environmental Research Laboratory. The U.S. Army Corps of Engineers, which uses a different measuring technique, calculated the September level at 4 inches below the record.
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During the summer and fall the drought expanded into the mid-Atlantic region. July, August, September, and November were especially dry months for this region.
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Pre-instrumental Drought Perspective
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 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 reports have been
prepared by the NOAA/NCDC Paleoclimatology and Climate Monitoring branches during 2007:
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- For all climate questions other than questions concerning this
report, please contact the National Climatic Data Center's Climate
Services Division:
Climate Services Division NOAA/National Climatic Data Center 151 Patton Avenue Asheville, NC 28801-5001 fax: 828-271-4876 phone: 828-271-4800 email: ncdc.info@noaa.gov
- For further information on the historical climate perspective presented in this report, contact:
Richard Heim NOAA/National Climatic Data Center 151 Patton Avenue Asheville, NC 28801-5001 fax: 828-271-4328 email: Richard.Heim@noaa.gov
-or-
Jay Lawrimore NOAA/National Climatic Data Center 151 Patton Avenue Asheville, NC 28801-5001 fax: 828-271-4328 email: Jay.Lawrimore@noaa.gov
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NCDC / Climate Monitoring / Climate of 2007 / Annual / Drought / Help
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