Pacific sea surface temperatures, midlatitude atmospheric circulation, and widespread interannual anomalies in western U.S. streamflow

Widespread droughts can have considerable impact on western United States (U.S.) streamflow but causes related to moisture delivery processes are not yet fully understood. Here we examine western U.S. streamflow records to identify robust leading modes of interannual variability and their links to patterns of ocean and atmospheric circulation. The leading mode of streamflow variability, a pattern of west-wide streamflow anomalies, accounts for approximately 50% of variability and is associated with persistent high-pressure anomalies related to ridges off the Pacific North American coast. The second mode of variability accounts for approximately 25% of variability and is associated with ocean and atmospheric conditions in the tropical Pacific. Our results suggest that the leading mode of streamflow variability in the western U.S. is more strongly associated with internally driven midlatitude atmospheric variability than equatorial Pacific sea surface temperatures.