DROUGHT AND REGIONAL HYDROLOGIC VARIATION IN THE UNITED-STATES - ASSOCIATIONS WITH THE EL-NINO SOUTHERN OSCILLATION

Using 94 years of monthly Palmer Drought Severity Index (PDSI) data fo r 344 climate divisions, this study investigates the hydroclimatic res ponse in the United States to the extreme phases of the Southern Oscil lation (El Nino and La Nina). Several regions of coherent response to El Nino-Southern Oscillation (ENSO) are identified. The strongest rela tionship between El Nino and extreme drought years is found in the Pac ific Northwest. A strong relationship is also noticed in the southern United States, where dry conditions occur consistently during La Nina events. Next, the conditional response in PDSI is evaluated based on t he extreme phases of the Southern Oscillation. The PDSI results were c ompared to similar analyses on 41 years of station temperature, precip itation, and streamflow data. A consistent response is seen in the oth er hydroclimatic variables, though the most filtered response is seen in PDSI data and streamflow data. The major contribution to the unders tanding of the ENSO-United States climate relationship is the evaluati on of the general form of drought and comparison of these results to t he fundamental hydrologic processes (precipitation, temperature, and s treamflow).