Abstract Rain-on-snow (ROS) events can trigger severe floods in mountain regions. There is high uncertainty about how the frequency of ROS events (ROS) and associated floods will change as climate warms. Previous research has found considerable spatial variability in ROS responses to climate change. Detailed global assessments have not been conducted. Here, atmospheric reanalysis data was used to drive a physically based snow hydrology model to simulate the snowpack and the streamflow response to climate warming of a 5.25 km 2 virtual basin (VB) applied to different high mountain climates around the world. Results confirm that the sensitivity of ROS to climate warming is highly variable among sites, and also with different elevations, aspects and slopes in each basin. The hydrological model predicts a decrease in the frequency of ROS with warming in 30 out 40 of the VBs analyzed; the rest have increasing ROS. The dominant phase of precipitation, duration of snow cover and average temperature of each basin are the main factors that explain this variation in the sensitivity of ROS to climate warming. Within each basin, the largest decreases in ROS were predicted to be at lower elevations and on slopes with sunward aspects. Although the overall frequency of ROS drops, the hydrological importance of ROS is not expected to decline. Peak streamflows due to ROS are predicted to increase due to more rapid melting from enhanced energy inputs, and warmer snowpacks during future ROS.

Abstract Rain-on-snow (ROS) events can trigger severe floods in mountain regions. There is high uncertainty about how the frequency of ROS events (ROS) and associated floods will change as climate warms. Previous research has found considerable spatial variability in ROS responses to climate change. Detailed global assessments have not been conducted. Here, atmospheric reanalysis data was used to drive a physically based snow hydrology model to simulate the snowpack and the streamflow response to climate warming of a 5.25 km 2 virtual basin (VB) applied to different high mountain climates around the world. Results confirm that the sensitivity of ROS to climate warming is highly variable among sites, and also with different elevations, aspects and slopes in each basin. The hydrological model predicts a decrease in the frequency of ROS with warming in 30 out 40 of the VBs analyzed; the rest have increasing ROS. The dominant phase of precipitation, duration of snow cover and average temperature of each basin are the main factors that explain this variation in the sensitivity of ROS to climate warming. Within each basin, the largest decreases in ROS were predicted to be at lower elevations and on slopes with sunward aspects. Although the overall frequency of ROS drops, the hydrological importance of ROS is not expected to decline. Peak streamflows due to ROS are predicted to increase due to more rapid melting from enhanced energy inputs, and warmer snowpacks during future ROS.

Abstract In this study we investigated the sensitivity of the snowpack to increased temperature and short-wave radiation, and precipitation change along an elevation gradient (1500–2500 m a.s.l.) over the main mountain ranges of the Iberian Peninsula (Cantabrian Range, Central Range, Iberian Range, Pyrenees, and the Sierra Nevada). The output of a meso-atmospheric model (WRF) was used as forcing data in a physically-based energy and mass balance snowpack model (FSM2). A cluster analyses was applied to the input data of the FSM2 model to identify a total of 12 cells that summarized the climatic variability of the mountain ranges. The WRF output was then rescaled to various elevation bands using an array of psychrometric and radiative formulae and air temperature lapse rates. A factorial experiment was performed to generate synthetic meteorological series involving gradual alteration of the temperature (0–4 °C increases), short-wave radiation (0–40 Wm-2 increases), and precipitation (variations of ±20%) to force the FSM2. We found differing sensitivities across the various mountainous areas as a consequence of differences in their energy and mass balances. The results showed a generally negative impact of climate warming on the magnitude, duration, and melt rates of the snowpack over all elevation bands, even under scenarios of greater precipitation. The average effect of warming on the duration of the snowpack ranged from −23% per °C at 1500 m a.s.l. to −13% per °C at 2500 m a.s.l., on the peak snow water equivalent ranged from −20% per °C at 1500 m a.s.l. to −15% per °C at 2500 m a.s.l., and on melt rates ranged from −9% to −6% per °C. The effect of increasing short-wave radiation on the snowpack ranged from approximately −2% per 10 Wm−2 at 1500 m a.s.l. to −1% per 10 Wm−2 at 2500 m a.s.l. for both the snowpack duration and peak SWE indices. The effect on the snowpack caused by precipitation changes reduced gradually with increasing elevation, especially in the colder areas. The response of the melt rates to warming was negative in most of the areas at all elevations, suggesting less intense but longer melt seasons.