Global shifts in the intensity spectrum of rain-on-snow events under climate warming

Rain-on-snow (ROS) events are increasingly recognized as a major cold-region hydrological hazard, yet global-scale assessments have largely focused on their overall frequency and have seldom distinguished event intensity or its drivers. Here, we use 1950-2024 ERA5-Land data to construct the first global ROS events identification framework with a physically informed, five-level intensity classification (Minor-Weak-Moderate-Severe-Extreme). By systematically analysis of global ROS events over the past 75 years, we reveal a robust intensity-dependent response to warming: Minor events exhibit the highest annual frequency, with a median of approximately 30 d/yr. Weak and Moderate events with medians of roughly 4.75 and 3.97 d/yr. Severe and Extreme events exhibit pronounced spatial polarization, intensifying across snow-dominated regions of western North America, Alaska, northern Europe, and Siberia. Minor and Weak events are primarily driven by enhanced rainfall, Moderate events by combined warming and rainfall-phase increases, whereas Severe and Extreme events require the concurrence of anomalously warm conditions, deep antecedent snowpacks, and intense liquid precipitation. Moreover, Severe and Extreme ROS events display stronger seasonal concentration, with March-May emerging as the global hot spot of Extreme ROS events. This study offers a new perspective for improving ROS flood risk prediction and water resource management.