THE RELATIONSHIPS BETWEEN UNITED-STATES STREAMFLOW AND LA-NINA EVENTS

In an earlier study of the teleconnection between streamflow and the warm (El Nino) phase of the El Nino/Southern Oscillation (ENSO) cycle, we found a strong relationship evident in four regions of the United States: the Gulf of Mexico, the Northeast, the North Central, and the Pacific Northwest. In this present study we have examined the same four regions for a relationship between streamflow and the cold (La Nina) phase of the Southern Oscillation (SO). Invariably, we found evidence of strong and consistent streamflow responses to La Nina events within the study regions. In each of the four regions, the strongest La Nina signal occurred at the same time of year as had the El Nino signal in their respective years. The sign of the seasonal streamflow anomaly associated with the La Nina events is the opposite of that associated with the El Nino events. This documents the existence of the biennial tendency related to the SO in the streamflow anomaly, which is expected, since La Nina/El Nino are opposite phases of the ENSO cycle. Finally, the relationships between streamflow and La Nina/El Nino were found to be statistically significant, based on the hypergeometric distribution. The results of this study demonstrate coherent, consistent, and significant midlatitude streamflow responses to the tropical SO phenomenon. This confirms the results of previous climatological studies that have examined the extratropical teleconnections from a hydrological and meteorological perspective.