A historical perspective on precipitation, drought severity, and streamflow in Texas during 1951-56 and 2011

The intense drought throughout Texas during 2011 resulted in substantial declines in streamflow. By April 2011, nearly all of the State was experiencing severe to extreme drought according to data from the University of Nebraska–Lincoln Drought Monitor. By the end of July 2011, more than 75 percent of the State was experiencing exceptional drought. The worst of the drought occurred around October 4, 2011, when 97 percent of Texas was suffering from extreme to exceptional drought. The historical drought of 1951–56 has long been used by water-resource managers, engineers, and scientists as a point of reference for water-supply planning. A comparison of drought conditions during the 2011 water year (October 1, 2010, through September 30, 2011) to the historical drought of 1951–56 from a hydrologic perspective serves as an additional reference for water-supply planning.

A record low statewide average annual precipitation of 11.27 inches for the period 1895–2011 was recorded during the 2011 water year; the prior record low statewide average precipitation was 13.91 inches during the 1956 water year. The statewide monthly Palmer Drought Severity Index (PDSI) declined to -7.93 during September 2011, which was larger in magnitude than the statewide PDSI during any drought-affected month in the 1950s.

Annual mean streamflow and streamflow-duration curves for the 1951–56 and 2011 water years were assessed for 19 unregulated U.S. Geological Survey (USGS) streamflow-gaging stations. At eight of these streamflow-gaging stations, the annual mean streamflow was lower in 2011 than for any year during 1951–56; many of these stations are located in eastern Texas. Annual mean streamflows for streamflow-gaging stations in the Guadalupe, Blanco, and upper Frio River Basins were lower in 1956 than in 2011. The streamflow-duration curves for many streamflow-gaging stations indicate a lack of (or diminished) storm runoff during 2011. Low streamflows (those exceeded 90 to 95 percent of days) were lower for 1956 than for 2011 at seven streamflow-gaging stations. For most of these stations, the lowest of the low streamflows during 1951–56 occurred in 1956. During March to September 2011, record daily lows were measured at USGS streamflow-gaging station 08041500 Village Creek near Kountze, Tex., which has more than 70 years of record. Many other USGS streamflow-gaging stations in Texas started the 2011 water year with normal streamflow but by the end of the water year were flowing at near-record lows.