Using 94 years of monthly Palmer Drought Severity Index (PDSI) data for 344 climate divisions, this study investigates the hydroclimatic response in the United States to the extreme phases of the Southern Oscillation (El Nino and La Nina). Several regions of coherent response to El Nino-Southern Oscillation (ENSO) are identified. The strongest relationship between El Nino and extreme drought years is found in the Pacific 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 the extreme phases of the Southern Oscillation. The PDSI results were compared to similar analyses on 41 years of station temperature, precipitation, and streamflow data. A consistent response is seen in the other hydroclimatic variables, though the most filtered response is seen in PDSI data and streamflow data. The major contribution to the understanding of the ENSO-United States climate relationship is the evaluation of the general form of drought and comparison of these results to the fundamental hydrologic processes (precipitation, temperature, and streamflow).
