Rain‐on‐Snow Events Frequently Drive Peak Streamflow Across the Contiguous United States

Abstract Rain‐on‐snow events occur when rain falls on a ripe snowpack, initiating rapid snowmelt that can produce extreme flooding in watersheds throughout the world. Rapid snowmelt during rain‐on‐snow flooding is primarily caused by the increase of net radiation (longwave) and turbulent fluxes during the event. The antecedent soil moisture can also limit infiltration of rain and snowmelt into the ground, resulting in increased runoff. Currently, the frequency and effect of rain‐on‐snow driven annual peak streamflows is not well defined for the Contiguous United States (CONUS). Our results highlight that rain‐on‐snow events regularly cause large floods across the CONUS. We show that rain‐on‐snow events contributed to ∼16% of all annual peak streamflows in snow‐affected watersheds throughout CONUS between 1982 and 2023. There is substantial regional variability in the number and magnitude of rain‐on‐snow‐influenced annual peak streamflows. However, in 57% of the watersheds included in the study, at least one top five annual peak flow event was rain‐on‐snow‐influenced. Changes in initial snowpack state (e.g., internal temperature) and precipitation timing and phase can increase the potential for rain‐on‐snow‐influenced flood events. Increasing the occurrence of these events adds uncertainty to both hydrologic and water management processes including flood risk management, groundwater recharge rates, and snowmelt runoff duration which are important for water supply and ecosystem functions.