A spatially resolved estimate of High Mountain Asia glacier mass balances, 2000-2016

Abstract

High Mountain Asia hosts the largest glacier concentration outside the polar regions. These glaciers are important contributors to streamflow in one of the most populated areas of the world. Past studies have used methods that can only provide regionally-averaged glacier mass balances to assess the High Mountain Asia glacier contribution to rivers and sea level rise. Here we compute the mass balance for about 92 % of the glacierized area of High Mountain Asia using time series of digital elevation models derived from satellite stereo-imagery. We calculate an average region-wide mass balance of -16.3 ± 3.5 Gt yr^-1 (-0.18 ± 0.04 m w.e. yr^-1) between 2000 and 2016, which is less negative than most previous estimates. Region-wide mass balances vary from -4.0 ± 1.5 Gt yr^-1 (-0.62 ± 0.23 m w.e. yr^-1) in Nyainqentanglha to +1.4 ± 0.8 Gt yr^-1 (+0.14 ± 0.08 m w.e. yr^-1) in Kunlun, with large intra-regional variability of individual glacier mass balances (standard deviation within a region ˜0.20 m w.e. yr^-1). Specifically, our results shed light on the Nyainqentanglha and Pamir glacier mass changes, for which contradictory estimates exist in the literature. They provide crucial information for the calibration of the models used for projections of future glacier response to climatic changes, models that presently do not capture the pattern, magnitude and intra-regional variability of glacier changes in High Mountain Asia.

Figure 1. High Mountain Asia major drainage basins.

The endorheic basins are in blue and the exorheic basins in red. The yellow triangles show the validation sites (named after the region or a summit) where we evaluated the glacier mass balance obtained with the ASTER method (see Supplementary Information and Fig. S4-7). The glaciers from the GAMDAM glacier inventory are shown in black.

Figure 2. Glacier elevation changes and mass balance for High Mountain Asia (2000-2016).

a- map of glacier mean elevation change on a 1°×1° grid. b- For each region in ref. , the distribution of glacier-wide mass balance for every individual glacier (> 2 km²) is represented in histograms of the number of glaciers (y-axis) as a function of MB (x-axis in m w.e. yr^-1). The black dashed line represents the area-weighted mean. The numbers denote the total number of individual glaciers (first), the corresponding total area (in km², second), the standard deviation of their mass balances (in m w.e. yr^-1, third) and the area weighted average mass balance (in m w.e. yr^-1, fourth). Initials of the respective regions are repeated in bold in the graphs.

Figure 3. Altitudinal distribution of glacier elevation change.

a- Rate of elevation change for the period 2000-2016 as a function of normalized elevation, which is defined as (z - z_2.5)/(z_97.5-z_2.5), where z is the elevation and z_2.5 and z_97.5 are the elevation of the 2.5 and 97.5 percentile of area, respectively. b- Rate of elevation change for the period 2000-2016 as a function of elevation (in m a.s.l.).