Effects of El Niño Southern Oscillation and Pacific Interdecadal Oscillation on Water Supply in the Columbia River Basin

Decadal climate variability in the form of the Pacific Interdecadal Oscillation (PDO) is analyzed with the El Niño Southern Oscillation (ENSO) to assess impacts on seasonal water supply in the Columbia River Basin and to test for statistical significance. The cross-correlation functions indicate a significant correlation between seasonal runoff and both the Southern Oscillation Index (SOI) and PDO, suggesting a time period where ENSO events have the most significant impact on the January through July volume runoff at The Dalles Dam. Correlation functions indicate volume runoff is directly related to SOI phase and inversely related to PDO phase. Results show there is a statistically significant change in the mean January through July volume runoff only when El Niño events occur during the positive phase of the PDO and when La Niña events occur during the negative phase of the PDO. Precipitation and temperature patterns are illustrated to explain this shift in the mean runoff. While slight shifts in variability are evident for the various climate conditions, significance tests show that the changes in variability do not differ significantly from the neutral condition.