Arizona precipitation response to the Southern Oscillation: A potential water management tool

As demand for water in the southwestern United States rises during the next century due to growing population pressure on limited water resources will intensify. Interannual variations in precipitation P are large throughout Arizona (AZ), and known to be influenced by the global-scale El Nino-Southe rn Oscillation (ENSO). Mean monthly P was compiled in each of seven AZ clim ate divisions for composites of 28 EI Nino and 23 La Nina years (1895-1994) , using 6-month (June-November) mean values of the Southern Oscillation Ind ex (SOI) to assign ENSO phase. Autumn, late winter and spring months in all AZ divisions averaged >50% higher P during El Nino than La Nina years. Man agement practices related to timing and relative proportions of surface wat er and groundwater withdrawals, based in part on ENSO conditions, are clear ly feasible in this region. Precipitation data from the central highlands o f AZ (NE of Phoenix) indicate decadal-scale trends in linear regression cor relation of autumn through spring P as a function of SOI. These trends incl ude higher P than the long-term mean since about 1960 for a given value of SOI.