2009-2010 El Nino: Predicted Hydrologic Response in the United States

摘要

The National Oceanic and Atmospheric Administration (NOAA) currently (as of October 2009) forecasts that the southern Pacific Ocean will experience El-Nino conditions in late 2009 into 2010. Evaluating historic El-Nino events similar to the current conditions suggests that some regions of the U.S. including the Southeast, Midwest and Southwest, will see improvement in surface water supply, while others including the Pacific Northwest will experience below average water supply conditions. The hydrologic data consists of 639 unimpaired streamflow stations for the continental U.S. and approximately 300 western U.S. snowpack stations. To determine similar historic El Nino events to the forecasted 2009-2010 El Nino, two statistical tests were performed. A similar El Nino event was defined when the monthly historic Nino 3.4 conditions and forecasted 2009-2010 Nino 3.4 conditions had a coefficient of determination (R2) exceeding 90% and the t-test of the difference of the means did not exceed 90%. Four historic El Nino events (1972-1973, 1982-1983, 1986-1987, and 2002-2003) were found to be similar to the forecasted 2009-2010 El Nino event. Yearly standardized anomalies (i.e., mean of zero and standard deviation of one) of the streamflow and snowpack data were used to evaluate the fluctuations from the means for year (1973, 1983, 1987 and 2003) following the El Nino event. The hydrologic response included March 1st, April 1st and May 1st snowpack and, seasonal and water-year streamflow. The results would be able to give recommendations to water managers regarding projected changes in water supply and the impacts to reservoir operations. Given the timing of the 2010 ASCE EWRI Conference (mid May), current 2010 hydrologic response will be compared to predicted (i.e., 1973, 1983, 1987 and 2003) response.