Near-Future Increases in Extreme Precipitation and Rain-on-Snow Events in Southeast Alaska

Landslides and floods in Southeast Alaska are often triggered by extreme precipitation associated with atmospheric rivers (ARs). In a warming climate, ARs are expected to become more frequent and intense across North America, yet the corresponding changes in extreme meteorological conditions in Southeast Alaska remain uncertain. This study used 4-km regional dynamical downscaling with the Weather Research and Forecasting (WRF) model to evaluate historical (1981–2019) and projected mid-century (2031–2060) changes in extreme meteorological variables linked to ARs. Mid-century projections show increases in 95th-percentile integrated vapor transport (IVT), 925-hPa wind speed, freezing level height, and precipitation, while extreme snow water equivalent (SWE) is expected to decrease. More frequent above-freezing temperatures indicate a shift toward less snow and more rain during ARs, increasing the likelihood of rain-on-snow (ROS) related hazards. ROS events are projected to become more frequent (+3 d yr-1) and intense (+40–60 mm d-1), consistent with regional warming and rising freezing levels. The combined increases in AR strength, precipitation intensity, and reduced SWE suggest growing potential for landslide-triggering conditions, underscoring the need for improved hazard forecasting and preparedness in Southeast Alaska.