Glacier mass balance and its climatic and non-climatic drivers in the Ladakh region during 2000-2021 from remote sensing data

The Ladakh region in the western Himalaya relies directly on snow-glacier-fed first order streams for domestic and agricultural needs of the population. Despite the significant contribution of glacier meltwater towards community livelihood and its vulnerability in a warmer climate, glaciers in the Ladakh region have not been studied comprehensively. Previous studies, mostly at a poor spatial (~90 m) and temporal (10-15 years) scales, focused only on geodetic glacier mass balance estimation, hence their controlling climatic drivers remain unknown. In this study, we estimate the geodetic mass balance of the glaciers of the Ladakh region, using multiple digital elevation models of 30 m resolution acquired between 2000 (Shuttle Radar Topography Mission; SRTM) and 2021 (Advanced Spaceborne Thermal Emission and Reflection Radiometer; ASTER). Due to the large aerial coverage, we divided the whole Ladakh region into two sub-regions namely the eastern and western Ladakh. The primary climatic drivers of glacier mass balances were examined using the long-term ERA5-Land reanalysis data, complemented by available in-situ meteorological data. The role of non-climatic (morphological) variables on glacier mass balances was also investigated in detail. The results reveal a negative glacier mass balance over the Ladakh region during the last two decades, with significant spatial variability. Glaciers in western Ladakh lost higher mass (-0.35 ± 0.07 to -0.37 ± 0.07 m w.e. a^-1) compared to eastern Ladakh (-0.21 ± 0.07 to -0.33 ± 0.05 m w.e. a^-1). Although the widespread mass loss in Ladakh is primarily caused by warming, the variations in spatial mass loss are primarily caused by the morphological settings of the glaciers. The eastern Ladakh glaciers are located at higher elevations and small sized, whereas western Ladakh glaciers are large sized and their tongues are situated at lower elevations (low-elevation-hypsometry), therefore, the impact of temperature is much higher in them, leading to higher mass loss. The non-climatic factors (morphological control) exhibit a dominant role than climatic factors in governing the glacier mass balances, particularly in the EL. The comparison between ASTER-based and the Ice, Cloud and land Elevation Satellite (ICESat)-2 laser altimetry-based mass balances shows a good agreement, reaffirming the robustness of regional mass balance estimates. Overall, glaciers of the Ladakh region are losing mass and the western Ladakh glaciers are potentially more susceptible to warming climate compared to the eastern Ladakh.