The USGS released a new report (right, cover photo from Prof. Paper 1703) yesterday entitled, "Ground-Water Recharge in the Arid and Semiarid Southwestern United States," with two study areas in southeast Arizona.
The editors conclude, "Analysis of recharge patterns shows that large expanses of alluvial basin floors are drying out under current climatic conditions, with little to no recharge to underlying ground water. Ground-water recharge occurs mainly beneath upland catchments in which thin soils overlie permeable bedrock, ephemeral channels in which flow may average only several hours per year, and active agricultural areas."
They also note that conditions produce "up to millennial time lags between changes in hydrologic conditions at the land surface and subsequent changes in recharge to underlying ground water."