Intensified snowmelt on Karakoram glaciers Revealed by Sentinel-1 Backscatter-Derived wet snow dynamics

Glacier surface melting critically drives glacier mass balance in the Karakoram, yet how wet snow evolves seasonally, altitudinally, and across glacier types remains poorly constrained, as optical observations are often limited by persistent cloud cover and complex topography. We developed a Sentinel-1 Synthetic Aperture Radar (SAR) time-series approach, optimized for complex high-mountain terrain to identify wet snow dynamics across Karakoram glaciers from 2017 to 2023. The results reveal a clear seasonal cycle, with wet snow generally peaking in July and occurring predominantly around 5,500 m a.s.l. The spatial evolution of wet snow shows a pronounced southwest–northeast melt gradient, closely linked to the seasonal migration of the 0 °C isotherm (R 2 > 0.95). Furthermore, glacier morphology significantly modulates these patterns: avalanche-fed Turkestan-type glaciers show earlier wet snow peaks and enhanced wet snow concentration in their middle-to-lower reaches, suggesting an important role of gravitational mass redistribution in altering local melt timing and surface hydrology. In addition, the upward migration of both wet snow boundaries over the study period indicates intensified surface melting. This trend provides a new surface-process perspective for understanding the recently reported transition or possible end of the Karakoram Anomaly. Our findings demonstrate the value of regionally adapted Sentinel-1 SAR observations for constraining heterogeneous glacier melt processes and high-mountain water-resource changes under a warming climate.