Abstract

Water Year 2006 (October 1, 2005, to September 30, 2006) was a year of extreme hydrologic drought and the driest year in the recent 2002–2006 drought in Oklahoma. The severity of this recent drought can be evaluated by comparing it with four previous major hydrologic droughts, water years 1929–41, 1952–56, 1961–72, and 1976–81. The U.S. Geological Survey, in cooperation with the Oklahoma Water Resources Board, completed an investigation to summarize the Water Year 2006 hydrologic drought and compare it to the four previous major hydrologic droughts in the 20th century.

The period of water years 1925–2006 was selected as the period of record because before 1925 few continuous record streamflow-gaging sites existed and gaps existed where no streamflow-gaging sites were operated. Statewide annual precipitation in Water Year 2006 was second driest and statewide annual runoff in Water Year 2006 was sixth driest in the 82 years of record.

Annual area-averaged precipitation totals by the nine National Weather Service Climate Divisions from Water Year 2006 are compared to those during four previous major hydrologic droughts to show how rainfall deficits in Oklahoma varied by region. Only two of the nine climate divisions, Climate Division 1 Panhandle and Climate Division 4 West Central, had minor rainfall deficits, while the rest of the climate divisions had severe rainfall deficits in Water Year 2006 ranging from only 65 to 73 percent of normal annual precipitation.

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First posted February 9, 2009