Understanding Decadal Variability of Atmospheric Rivers

How does decadal climate variability change the nature and predictability of atmospheric rivers? Decadal swings in atmospheric river frequency or shifts in the proportion of precipitation falling as rain could challenge current water resource and flood risk management practice. Physical multi-scale processes operating between Pacific sea surface temperatures (SSTs) and atmospheric rivers over the Western U.S. are explored using the global Model for Prediction Across Scales (MPAS). A 60km global mesh is refined over the Western U.S. to 15km to capture the major terrain effects on precipitation. Ensemble seasonal simulations are run under three global SST scenarios: the positive phase of the Interdecadal Pacific Oscillation (IPO), the negative phase of the IPO, and a control scenario representative of climatology. Initial analysis shows significant latitudinal shifts in Western U.S. AR landfall location, with the positive phase of the IPO driving twice the number of strong ARs over Southern California. Dynamic and thermodynamic mechanisms behind these major changes will be presented. Given recent evidence that we have entered a positive phase of the IPO, implications for current reservoir management practice over the next decade will be discussed. This work contributes to the NSF-funded project UDECIDE (Understanding Decision-Climate Interactions on Decadal Scales). UDECIDE brings together practitioners, engineers, statisticians, and climate scientists to understand the role of decadal climate information for water management and decisions.