The influences of Type 1 El Nino and La Nina events on streamflows in the Pacific southwest of the United States

The hydroclimatic signals associated with either extreme phase of the Southern Oscillation (SO) are explored based on data from 50 streamflow stations in California, Arizona, New Mexico, Colorado, and Utah. A significant level for the results is assessed by the use of a hypergeometric distribution. Highly significant, coherent signals are demonstrated to exist for both events, with opposite sign and almost identical timing. Pacific Southwest streamflow responses to the T1ENSO thermal forcing are characterised by a wet December-July season in the subsequent year of the event. Similarly, a dry February-July season is detected as a period at which the La Nina-streamflow relationship is strong and spatially coherent. -from Authors