Quantification of Glacial Ice Mass Loss in the Himalaya since the Little Ice Age

Understanding glacier mass change over time is of critical importance, having both local and global implications, specifically those of water security and of sea-level rise. The Little Ice Age (LIA) was a period of cooler temperatures, causing the last general growth of glaciers globally. Within the Himalaya the LIA maximum occurred ~1300–1600 AD, following which there was a general recession of glacial mass in response to warming temperatures. This study aimed to quantify the magnitude and rate of this recession within the central and eastern Himalaya, using the newly released 8m HMA DEM. The interregional variability of this change was also considered in relation to topographic effects and glacier terminus conditions. Mass change estimates were derived using geomorphological mapping and the reconstruction of palaeo-glacier ablation zones through interpolation techniques. Cumulative area change within the east and central Himalaya was -4,957.9 km2 ± 118.5 km2 (30.7 ± 0.7%) with a volume change of -287.5 ± 58.9 km3, equivalent to a mass of 244.45 ± 67.17 Gt, accounting for 0.68 ± 0.19 mm SLE. Annually the total mass budget from 1450 AD to 2013 was estimated as 0.43 ± 0.12 Gt yr-1, equating to 0.0012 ± 0.0003 mm yr-1 from glacial melt. It was found that glacier area (during the LIA), maximum elevation, minimum elevation, elevation range, compactness and aspect could explain 42% of the mass change variability seen. Debris-covered glaciers contributed the most to absolute volume change due to their lower average minimum elevations, while lake-terminating glaciers incurred the most average glacier elevation lowering, likely due to thermal undercutting and calving processes. This is the first study of its kind to encompass a large spatial area within the Himalayas since the LIA, presenting a baseline for change within the Himalayas from their last period of growth.