Assessing Glacier Mass Loss in the Alaknanda Basin of Garhwal Himalaya, during 2000-2017

Glaciers are an important indicator of climate change and also contribute significantly towards global mean sea-level rise. Himalayan glaciers in particular, are also an important source of freshwater to major river systems like Indus, Ganga and Brahmaputra. Hence, glacier mass loss has cascading effect on the heavily populated downstream regions of these rivers. Here, we estimate the mass budget of 61 glaciers (~316 ± 16 km²) in the Alaknanda basin of Garhwal Himalaya, for the period of 2000-2017, using satellite-based geodetic technique. We have utilized 5 Cartosat-1 stereo pairs to compute high resolution DEMs of the basin for 2011, 2014 and 2017 and differenced them with the global SRTM DEM of 2000, in order to estimate time variations of elevation change and glacier mass budget. The accuracy of the computed DEMs were improved utilizing DGPS data available in the two benchmark glaciers (Sathopanth (SPG) and Bhagirath Karakh (BGK)) in the basin. Results reveal significant mass loss in both SPG (-0.57 ± 0.06 m w.e/a) and BGK (-0.56 ±0.06 m w.e/a) during the years 2000-2017, which may be influenced by the presence of extended debris cover and supraglacial lakes in the ablation zone of these glaciers. Our results also compare well with an earlier estimate of glaciologic mass budget (-0.5 ± 0.6 m w.e/a) for SPG. The basin-wide mean mass budget for the period of 2000-2011 (with 11 glaciers) varies from 0.03 ± 0.07 m w.e/a to -0.56 ± 0.08 m w.e/a, while those for 2000-2014 (with 19 glaciers) and 2000-2017 (with 31 galciers) ranges from 0 ± 0.06 m w.e/a to -0.44 ± 0.06 m w.e/a and -0.02 ± 0.05 m w.e/a to -0.81 ±0.07 m w.e/a respectively. The present study reveals sustained mass loss of the glaciers in the Alakanda basin. The results presented here have important implications for improved understanding of the glacier dynamics, that would help to identify the behaviour of Himalayan glaciers in response to climate change.