Analyzing the Effects of Climate Change on Pacific Atmospheric River Behavior with MPAS

Annual precipitation along the west coast of North America is largely influenced by Atmospheric River (AR) events, which have been demonstrated in prior research to comprise a larger portion of extreme precipitation events in this region with future climate projections. There has been growing interest in the future changes of these ARs due to their large impacts on the water supply and flooding control in this region. In this study, we utilized the Model for Prediction Across Scales (MPAS) to simulate global weather patterns for selected years with higher resolution focused on the Northern Hemisphere. We then compared the ARs in the simulations with current climate conditions to those in the simulations with predicted future climate conditions, including adjusted sea-surface temperatures, CO2 concentrations, and sea ice fields, according to the Representative Concentration Pathway (RCP) 8.5 emissions scenario. Comparing the future climate simulation to the current climate simulation, MPAS depicts more frequent AR conditions across most regions of the North Pacific and the west coast of North America in all seasons. The intensity of ARs, which is measured as the maximum integrated water vapor transport (IVT) of each AR, exhibits a significant increase under future climate conditions. Furthermore, there is a notable northward shift of the maximum frequency of ARs over the North Pacific, which may be related to the poleward shift of the North Pacific storm track. These results reflect the thermodynamic effects projected to accompany climate change and the related impacts on AR behaviors that are particularly relevant for volatile hydro-climate regions that are vulnerable to precipitation extremes, such as California.