Glacier inventory and glacier changes (1994-2020) in the Upper Alaknanda Basin, Central Himalaya

Himalayan glaciers have been shrinking and losing mass rapidly since 1970s with an enhanced rate after 2000. The shrinkage is, however, quite heterogeneous and it is important to document individual glacier characteristics and their changes at the basin scale. We present an updated glacier inventory of the Upper Alaknanda Basin (UAB), Central Himalaya for the year 2020 and report area, debris cover and length changes for the periods 1994-2006 and 2006-2020 based on remote-sensing data. We identified 198 glaciers, comprising an area of 354.6 +/- 8.5 km(2), and classified them according to their size and morphology. The glaciers of the basin lost 4.2 +/- 2.9% (0.16 +/- 0.11% a(-1)) of their frontal area (from 368.6 +/- 9.2 to 353.0 +/- 5.3 km(2)) from 1994 to 2020. The average retreat rate was higher in the period 2006-2020 (13.3 +/- 1.8 m a(-1)) in comparison to 1994-2006 (9.3 +/- 1.9 m a(-1)). However, the area change rate was similar for the two periods (0.14 +/- 0.27% a(-1) for 1994-2006 and 0.16 +/- 0.19% a(-1) for 2006-2020). The debris-covered area has increased by 13.4 +/- 4.4% from 1994 to 2020. A comparison with previous studies in UAB indicates consistent area loss of similar to 0.15% a(-1) since the 1960s.