Finding the turning point and main driver of a disappearing Himalayan glacier

Glacier AX010 in the Shorong region is an iconic glacier in the Nepal Himalaya, observed since 1978. We conducted a drone photogrammetry survey in November 2023 and evaluated its volume change since 2008 as –1.3 m yr^–1, one of the fastest (and accelerating) shrinking rates in the Himalayas. We reconstructed the annual mass balance using the ERA5 reanalysis climate data and a glacier mass balance model, GLIMB. We first evaluated the ERA5 meteorological variables with our recent in-situ observational data of a nearby site (2022-2023). Secondly, we calibrated the ERA5 precipitation to yield the observed geodetic mass balance and reconstructed the annual mass balance over the past 83 years (1940-2023). The estimated mass balance and calibrated temperature were validated with the observational data in the 1970s and 1990s. We also estimated the ideal temperature by which the glacier could maintain equilibrium states. Trend and breakpoint analyses revealed that the temperature warming and glacier shrinkage started in the mid-1970s while precipitation has been rather stable throughout the entire period. These results suggest that temperature warming is the main driver for the glacier shrinkage.