Examining the impact of climatic and non-climatic attributes on glacier mass budget and surging in Alaknanda Basin, India

 Glacier meltwater is a significant component of the regional runoff In High Mountain Asia (HMA),. However, the majority of the HMA's glaciers are rapidly losing their mass, putting the long-term viability of meltwater as a component of river flow at risk. It is, hence, crucial to comprehend the long-term glacier response to climate change at the regional scale as well as the impact of non-climatic characteristics like morpho-topographic factors on ice loss. We estimate changes for 445 glaciers in the upper Alaknanda basin and neighboring transboundary glaciers using multi-temporal optical satellite images from 1973 to2020. Our measurements indicate a mean annual area change of −1.14 ± 0.07 m a^–1 and a geodetic glacier mass balance of −0.34 ± 0.08 m w.e.a^–1 for the whole period. Before 2000 (1973-2000), the mean regional glacier mass loss rate was -0.30 ± 0.07 m w.e.a^-1, which increased to -0.43 ± 0.06 m w.e.a^-1 during 2000-2020. The mass loss increased further (-0.68 ± 0.09 m w.e.a^-1) in the recent period (2015-2020) and we observed heterogeneous mass loss both in spatial and temporal scales. Our analysis revealed that the current significant glacier imbalance is probably a result of the rising temperature trend as revealed from the ERA5 Land reanalysis data. An extended ablation season due to the strong seasonal temperature increase has further accelerated glacial mass loss. Steep and higher elevation glaciers were less affected by negative mass budget. This can be explained beside the lower average temperatures at higher elevation by a rapid transfer of snow and ice that helped them to readjust their geometry compared to glaciers at lower elevation, having more gentle slopes and lower dynamics. Such low elevation glaciers are unlikely to recover in coming decades if the current trend of warming continues. We also identified a surging glacier draining onto the Tibetan Plateau that advanced rapidly by around 800 m within three months in Sep-Dec 2019. The advance is still ongoing, though at a much-reduced rate. Our temporally detailed measurements of glacier change provide an in-depth view of glacier evolution in the Alaknanda Basin and will improve the estimation of meltwater run-off component of the hydrological cycle.