Forecasting of Lower Colorado River Basin Streamflow using Pacific Ocean Sea Surface Temperatures and ENSO

The lower Colorado River basin is located in an area of known El Niño-Southern Oscillation (ENSO) influence. A streamflow forecast is developed using Pacific Ocean Sea Surface Temperatures (SSTs) as predictors in addition to a traditional ENSO predictor, such as the Southern Oscillation Index (SOI). Significant regions of SST influence on streamflow were determined using linear correlations (LC). These significant SST regions are then used as predictors in a statistically based exceedance probability model previously applied to streamflow stations in Australia and the U.S. Long lead-time (3 and 6 month) streamflow forecasts were developed for El Niño, La Niña and non-ENSO years for the winter-spring (January-February-March – JFM) season. The use of the SSTs resulted in improved forecasts, based on cross-validated skill scores, when compared to forecasts using the SOI. Additionally, forecast leadtimes were increased when using the SSTs as predictors due to the inability of the SOI to provide an acceptable forecast. Also, the use of SSTs provided an improved forecast for all lead times for non-ENSO seasons when compared to the SOI forecasts. Following the methodology presented, water resource planners in ENSO influenced areas are provided a useful tool for forecasting streamflow. Introduction One of the most well understood atmospheric/oceanic patterns relevant to climate variability in the western United States is the El Niño-Southern Oscillation (ENSO). ENSO refers to the interaction of El Niño, defined as the periodic large scale warming of the central-eastern equatorial Pacific Ocean, with the Southern Oscillation, the large scale climate variations existing in the tropical Pacific (Philander, 1990). ENSO phenomenon causes, simultaneously, droughts in Australia, New Zealand, and Southern Africa and devastating floods in North America, Peru, and Ecuador (Ropelewski and Halpert 1987). In the western United States, El Niño events are associated with below-normal streamflow in the Pacific Northwest, while at the same time there is above-normal streamflow in the southwest (e.g., Cayan and Peterson, 1989; Redmond and Koch,