Characterization of rain-on-snow events in the Cantabrian Mountains (1985–2020)

Abstract Rain-on-snow (ROS) events represent a key hydrometeorological process in mountainous regions, where liquid precipitation falling onto an existing snowpack can strongly enhance runoff generation and flood risk. Despite their relevance, ROS dynamics remain poorly documented in many mid-latitude mountain ranges. This study provides the first characterization of ROS events in the Cantabrian Mountains (northwestern Iberian Peninsula) over the period 1985–2020. Using CERRA-Land reanalysis data, ROS events were identified based on liquid precipitation thresholds and snowpack depletion. A total of 501 ROS episodes were detected, exhibiting pronounced interannual variability and a clear linkage with elevation, with maximum frequencies concentrated on high-altitude central massifs. Seasonal patterns reveal widespread ROS occurrence during winter, whereas autumn and spring events are increasingly restricted to elevations above ~ 1200 m. Synoptic classification using geopotential height, temperature, and sea-level pressure fields identified five dominant weather types, primarily associated with Atlantic air-mass advection. Trend analysis indicates weak but spatially coherent increases in ROS frequency at elevations above ~ 1000 m, particularly in winter, contrasted by neutral or negative tendencies at lower elevations. These findings highlight links between ROS occurrence and elevation, atmospheric circulation and ongoing changes in temperature and precipitation phase, with important implications for future hydrological management in temperate mountain areas.