Observed heterogeneous glacier mass loss for last two decades with a recent surge activity in Alaknanda Basin, Garhwal Himalaya, and its surroundings

Ongoing climate warming has given glacier thinning and recession over the last few decades along the Himalayan Arc, which has in turn led to severe glacier related hazards and affect glacier run-off in the downstream. The rapid melting of these mountain glaciers in the present climatic setting may cause large contributions not only to rising sea level but also the glacier run-off is important source for eco-system, agriculture, domestic and industrial water usage etc. in the downstream. Therefore, understanding of ice mass loss mechanisms in the region needs detailed observation. In this study we employ geodetic methods to estimate glacier mass balance of more than 200 glaciers, with 750 sq. km of glacier area and elevation varies from 3580 m to 7690 m, in the Alaknanda Basin, Garhwal Himalaya, and its surroundings for last two decades (2000-2020) using stereo satellite data, such as ASTER, SPOT-7, Pléiades. ASTER imageries of 2000 revealed that nearly 77% of the 222 investigated glaciers in Alaknanda Basin had debris covered tongues and overall glacier lost 7.6 sq. km area during 2000-2020. Our results showed a sustained mass loss of -0.55 0.12 m w.e.a-1 (8.3 2.1 Gt) for 222 glaciers from 2000-2020. The maximum mass loss occurred during 2015-2020 (-0.67 0.14 m w.e.a-1) when compared to previous time spans (-0.54 0.13 m w.e.a-1 for 2006-2015 & -0.39 0.14 m w.e.a-1 for 2000-2006). The Satopanth and Bhagirath Kharak glaciers, one of the well documented glaciers in this region, lost considerably more mass (-0.67 0.12 m w.e.a-1) as compared to the mean mass loss of this region during the entire observation period. We also highlight anomalous surge activity of a glacier (RGI60-14.26971) since 2017- the first example of surge activity in the region. The glacier advanced 838 56 m and thickening by a mean value of 13.1 2.2 m a-1, approximately 3.5 kilometers from its snout position, during 2017-2020. Further investigation is needed to confirm the anomalous behavior of the surging activity.