Predicting the Interannual Variability of California's Total Annual Precipitation

Understanding and predicting precipitation characteristics on seasonal and longer timescales can help California prepare for long-term droughts and precipitation extremes. We find that interannual variations in total precipitation across California are primarily determined by precipitation frequency. As was shown previously for total precipitation, the precipitation frequency is linked to the North Pacific jet stream location. This indicates that California precipitation frequency is primarily controlled by where the jet guides precipitate weather systems rather than how moist or energetic the systems are. The jet's position, in turn, depends on the states of the El Niño-Southern Oscillation (ENSO) and of the Pacific Decadal Oscillation (PDO). We use this to construct a regression model that predicts variations in California's annual total precipitation and precipitation frequency. Up to 20% of the wintertime precipitation variance in Southern California is predictable using decorrelated ENSO and PDO indices in the previous summer.