Understanding the Gangotri glacier dynamics: Implications from a fully distributed inversion of equivalent water-volume change

Abstract. The Gangotri Glacier is scientifically controversial regarding its dynamics, ice thickness, volume, and mass balance due to the lack of field data. Evidence of rapidly increasing temperatures with climate change is clearly visible in the concerning mass changes of Himalayan glaciers. Subsequently, monitoring glacier volumes is critical for managing regional water resources and predicting glacier dynamics. The Gangotri glacier, a significant water resource for northern India, is experiencing significant changes due to climate change. This study emphasizes its dynamic nature from 2016 to 2023. Ice thickness distribution of Gangotri glacier estimated using velocity and shear stress-based approach. Sentinel-2 multi-spectral imagery is used to estimate glacier velocity with three different approaches for comparative assessment of the ice dynamics based on pixel-wise cross-correlation. A laminar flow-based approach is applied to determine the thickness of the Gangotri Glacier. The thickness change of the study period is used to estimate the mass balance and equivalent water volume change of the glacier. The observed velocity ranged from 31 ± 5.8 - 81 ± 15.12 ma^-1 in the accumulation area to 15 ± 2.8 - 28 ± 5.23 ma^-1 near the snout, and the thickness varied from 580 ± 74.47 m in the upper reaches to 70 ± 9 - 115 ± 14.77 m near the snout. Through this study, we found that the mass wastage of the glaciated ice during the study period was -1.01 ± 0.403 m w.e. a^-1 (meter water equivalent)^, and the mean glaciated ice volume was 19.70 ± 2.64 km³. We observed the volumetric change is a declining pattern of the study period 2017 to 2023 gradually. The climatic parameters observed an increasing trend over the last two decades. We also found that the Apparent Thermal Inertia (ATI) increased which determined the debris accumulation over the ablation zone significantly from the side wall of the glacier due to fluctuation of the temperature differences (Thaw-freezing). These changes denote a significant reduction in the water storage capacity of the Gangotri Glacier.