UNITED-STATES STREAMFLOW PATTERNS IN RELATION TO THE EL-NINO SOUTHERNOSCILLATION

The relationship between the El Nino/Southern Oscillation (ENSO) and u nimpaired streamflow over the contiguous United States is studied. The extreme phases of the Southern Oscillation have been linked to fairly persistent classes of atmospheric anomalies over the low and middle l atitudes at regional and global scales. Of particular interest in this investigation is the identification of regions of land that appear to have strong and consistent ENSO-related streamflow signals. The first harmonic extracted from a 24-month ENSO composite at each station is assumed to be the ENSO-related signal appearing in streamflow anomalie s. These regions were identified by the similarity in phase of the har monic vectors. The vectorial display of these harmonics over a map of the United States provides the areal extents of ENSO influence on stre amflow. Coherent and significant streamflow responses to hypothesized ENSO forcing are found in four regions of the United States: the Gulf of Mexico, the Northeast, the North Central, and the Pacific Northwest . Once an ENSO event sets in, a long-range forecasting utility may be available for these regions. The results of this analysis, which are c onsistent with previous studies on precipitation and temperature, demo nstrate the mid-latitude hydrologic response to the tropical ENSO phen omena.