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Scientific Investigations Report 2008-5199

Prepared in cooperation with the Oklahoma Water Resources Board

Hydrologic Drought of Water Year 2006 Compared with Four Major Drought Periods of the 20th Century in Oklahoma

By Robert L. Tortorelli


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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.

See Report PDF for full abstract.

First posted February 9, 2009

For additional information contact:

Director, USGS Oklahoma Water Science Center
202 NW 66th St., Bldg. 7
Oklahoma City, OK 73116

Part or all of this report is presented in Portable Document Format (PDF); the latest version of Adobe Reader or similar software is required to view it. Download the latest version of Adobe Reader, free of charge.

Suggested citation:

Tortorelli, R.L., 2008, Hydrologic drought of Water Year 2006 compared with four major drought periods of the 20th century in Oklahoma: U.S. Geological Survey Scientific Investigations Report 2008–5199, 46 p.




Precipitation by Climate Division

Streamflow of Long-Term Sites

Effects of Low Streamflows


Selected References


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