In Northern California, much of the precipitation and surface water comes from atmospheric rivers–corridors of moisture transport from the tropics. The frequency of atmospheric rivers is cyclical, with periods of water surplus and deficit in the region that repeat every 10–17 years. This pronounced wet/dry cycle in this area of the Western United States is mainly attributed to regular fluctuations in sea surface temperatures in the tropical Pacific Ocean.
While many social and political factors influence water resource distribution, understanding the climate factors that regulate water availability is important for managing water in the future. This analysis provides a potential source of predictability for atmospheric river frequency, and thus water availability, years before a winter season.
The observational analysis highlights three important features for AR frequency on quasi-decadal scales:
A warming of the Central Pacific that accentuates the Aleutian Low 2–3 years before the peak of quasi-decadal AR frequency
A transition from central Pacific warming to eastern Pacific-type ENSO, and the associated eastward shift of the Aleutian Low to a position that facilitates positive IVT anomalies over Northern California
A consistent oscillation of the Aleutian Low over 10- to 17-year periods in tandem with the tropical Pacific warming/cooling, modulating AR frequency and wet-season moisture transport.