Recent warming of US West Coast Atmospheric Rivers
Are US West Coast atmospheric rivers getting warmer? If so, this could potentially alter the critical rain/snow balance in snowpack-dependent watersheds and cause precipitation at higher elevations to fall as rain rather than snow. Not only would warmer, primarily rain-producing atmospheric rivers greatly affect snow accumulation, but they might also increase the intensity of runoff, the potential for flooding, and the occurrence of rain-on-snow events.
We assess trends in cool season atmospheric river temperatures that occurred 1980-2016 over the Pacific Coast states of California, Oregon, and Washington. We also compare atmospheric river temperature trends to regional background temperature trends and trends in along-track atmospheric river temperature. We find overall atmospheric river warming over this period and particularly robust warming in October, November, and March atmospheric rivers. Atmospheric river warming appears to not be solely scaling to either local background temperature or along-track trends.
Flavors of Atmospheric Rivers:
Moisture or wind dominated?
Left: Atmospheric rivers event conditions on the wind (x-axis) and moisture (y-axis) spectrum, colored by "Moisture Dominance". Right: Precipitation composite of wet vs. windy high-IVT ARs.
Gonzales et al., (2020), Geophysical Research Letters
Strong integrated vapor transport (IVT) has been recognized as the defining characteristic of AR intensity, with AR strength often categorized by an event’s IVT and storm impacts often scaling close to IVT. However, ARs associated with similar IVT may yield very different impacts due to subtle but important differences in other AR characteristics. We quantify the relative distribution of moisture-dominated vs. wind-dominated (“wet” vs. “windy”) ARs across the west coast of North America. We quantify the seasonal and geographic distribution of AR types, and assess the relative impacts of wet vs. windy ARs upon landfall. We also investigate pre-landfall characteristics that govern the resulting AR flavor, including source regions and pathways of ARs.