Rainfall-Driven Extreme Snowmelt Will Increase in the Tianshan and Pamir Regions Under Future Climate Projection

Abstract

Snowmelt and related extreme events can have profound natural and societal impacts. However, the studies on projected changes in snow-related extremes across the Tianshan Mountains (TS) and Pamir regions have been underexplored. Utilizing regional climate model downscaling and bias-corrected CMIP6 data, this study examined the changes in snowmelt and water available for runoff (SM_ROS, rainfall plus snowmelt) during the cold seasons across these regions for historical (1994–2014) and future (2040–2060) periods under shared socioeconomic pathway (SSP) scenarios (SSP245 and SSP585). The results demonstrated that accumulated snowmelt was projected to rise by 17.98% and 20.36%, whereas SM_ROS could increase by 26.97% and 28.95%, respectively, under SSP245 and SSP585 scenarios. Despite relatively minimal changes in extreme snowmelt, the magnitude of the historical daily maximum extreme SM_ROS (10-year return level) was 28.04 mm and was expected to increase by 15.32% and 15.31% under the SSP245 and SSP585 scenarios, respectively, especially in western TS exceeding 26%. Meanwhile, areas with a daily extreme SM_ROS exceeding 50 mm could rise by over 13.5%. A notable rise in daily extreme SM_ROS and its area occupation in high intensity highlighted an increased risk of rainfall-driven extreme snowmelt events. The absolute increase in snowfall and frequent snow-rain phase transitions during the cold season under climate warming (SSP245: 2.19°C and SSP585: 2.22°C) benefits the increase in high-intensity rain-on-snow events, leading to extreme SM_ROS augmentation. The findings emphasize the significant role of rainfall-trigger snowmelt events in exacerbating extreme snowmelt in a warming climate.