Spatial variability in mass loss of glaciers in the Everest region, central Himalaya, between 2000 and 2015

The mass balance of most Himalayan glaciers is currently negative, and has been for several decades. Region wide averaging of mass change estimates masks any catchment or glacier scale variability in glacier recession, thus the role of a number of glaciological processes in glacier wastage remain poorly understood. We quantify mass loss rates between 2000 and 2015 for 32 glaciers in different catchments across the Everest region, and examine the role of 7 proglacial and 2 supraglacial glacial lakes in glacier mass loss. We also assess how future ice loss is likely to differ depending on glacier hypsometry. Spatially variable ice loss occurred within and between the Dudh Koshi (DK) and Tama Koshi (TK) catchments and on the Tibetan Plateau (TP) over the study period. The mean mass balance of the 32 glaciers was -0.53 ± 0.42 m w.e.a-1. The mean mass balance of the 9 lacustrine terminating glaciers (-0.70 ± 0.44 m w.e.a-1) was 32 % more negative than land-terminating glaciers in our sample. The mass balance of lacustrine-terminating glaciers is highly variable (-0.47 ± 0.35 m w.e. a-1 to -0.95 ± 0.52 m w.e. a-1) and we suggest that such a range reflects glacial lakes at different stages of expansion. Rates of mass loss are likely to increase as glacial lakes expand and calving can occur in deeper water. Using predicted IPCC AR5 warming scenarios, and considering variable glacier hypsometry in each catchment, we assess the effect of temperature increases on current glacier accumulation-area ratios (AARs; DK- 0.37, TK- 0.36, TP- 0.40). RCP 4.5 warming (0.9-2.3 oC by 2100) would reduce these AARs to between 0.25 and 0.03 in the TK, 0.26 and 0.18 in the DK, and 0.30 and 0.17 on the TP, respectively. Our results suggest that further glacial lake growth and/or expansion across the Himalaya is likely to be accompanied by increased ice mass loss. Further, the influence of temperature increases may be highly variable between catchments, complicating the prediction of the future contribution of glacial meltwater to river flow.