Recent warming of landfalling atmospheric rivers along the west coast of the United States

We detect monthly scale warming of >2 °C, with the most widespread warming occurring in November and March. To understand the causes of AR warming, we quantify the density of AR tracks from genesis to landfall and analyze along-track AR temperature for each month and landfall region. We investigate three possible influences on AR temperature trends at landfall:along-track temperatures prior to landfall, background temperatures over the landfall region, and AR temperature over the coastal ocean adjacent to the region of landfall.

Generally, AR temperatures at landfall more closely match coastal and background temperature trends than along-track AR temperature trends. The seasonal asymmetry of the AR warming and the heterogeneity of influences have important implications for regional water storage and flood risk—demonstrating that changes in AR characteristics are complex and may not be directly inferred from changes in the background climate.