Rain-on-snow (ROS) events significantly influence hydrological extremes, while their future dynamics across the Tianshan and Pamir regions remain insufficiently assessed. This study utilized WRF dynamically downscaling simulations driven by bias-corrected CMIP6 data to investigate changes in ROS characteristics and water available for runoff contributions during the historical (1995-2014) and mid-century (2041-2060) periods under SSP245 and SSP585 scenarios. Results showed that the historical average annual ROS frequency, daily maximum ROS intensity, and total annual ROS intensity were 1.86 days, 13.52 mm, and 46.02 mm, respectively, with the highest ROS frequency occurring at elevations between 2250 and 2500 m. Regionally, ROS activity was most intense along the windward slopes of the Western Tianshan, Northern Tianshan, and Western Pamir. Seasonally, events peaked in spring, comprising 50.64 % of annual occurrences, with higher contributions in the Pamir (57.09 %) and Western Tianshan (52.65 %). The above indices were projected to increase by 49.57 %, 43.39 %, and 65.67 % under SSP245 and by 49.33 %, 45.44 %, and 66.63 % under SSP585. The annual contribution of snowmelt to total water available for runoff declined by 11.97 percentage points (pp) and 11.39 pp under SSP245 and SSP585 scenarios, respectively, indicating a reduced role of snow-driven runoff processes. In contrast, ROS-induced snowmelt contributions to total snowmelt climbed by 1.42 pp and 1.46 pp; consequently, the ROS intensity's contribution to water available for runoff increased by 1.32 pp and 1.35 pp under the respective scenarios. These shifts were primarily driven by increased annual precipitation (295 and 288 mm), decreased snowfall/precipitation ratio (-8.53 pp and -8.30 pp), and increased all intense rainfall events (11.63 and 11.36 days) under warming (2.49 and 2.51 degrees C). Consequently, the hydrological system became more susceptible to ROS-driven extreme events. These findings revealed an increased risk of ROS-induced flooding potential under climate warming and underscored a potential seasonal mismatch between runoff supply and water demand in arid alpine regions.