Glaciers are among the best indicators of terrestrial climate variability, contribute importantly to water resources in many mountainous regions1,2 and are a major contributor to global sea level rise3,4. In the Hindu Kush–Karakoram–Himalaya region (HKKH), a paucity of appropriate glacier data has prevented a comprehensive assessment of current regional mass balance5. There is, however, indirect evidence of a complex pattern of glacial responses5,6,7,8 in reaction to heterogeneous climate change signals9. Here we use satellite laser altimetry and a global elevation model to show widespread glacier wastage in the eastern, central and south-western parts of the HKKH during 2003–08. Maximal regional thinning rates were 0.66 ± 0.09 metres per year in the Jammu–Kashmir region. Conversely, in the Karakoram, glaciers thinned only slightly by a few centimetres per year. Contrary to expectations, regionally averaged thinning rates under debris-mantled ice were similar to those of clean ice despite insulation by debris covers. The 2003–08 specific mass balance for our entire HKKH study region was −0.21 ± 0.05 m yr−1 water equivalent, significantly less negative than the estimated global average for glaciers and ice caps4,10. This difference is mainly an effect of the balanced glacier mass budget in the Karakoram. The HKKH sea level contribution amounts to one per cent of the present-day sea level rise11. Our 2003–08 mass budget of −12.8 ± 3.5 gigatonnes (Gt) per year is more negative than recent satellite-gravimetry-based estimates of −5 ± 3 Gt yr−1 over 2003–10 (ref. 12). For the mountain catchments of the Indus and Ganges basins13, the glacier imbalance contributed about 3.5% and about 2.0%, respectively, to the annual average river discharge13, and up to 10% for the Upper Indus basin14.
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We thank G. Cogley and A. Gardner for their exceptionally thorough and constructive comments. This study was supported by the European Space Agency (ESA) through the projects GlobGlacier (21088/07/I-EC) and Glaciers_cci (4000101778/10/I-AM). The study is further a contribution to the Global Land Ice Measurements from Space (GLIMS) initiative and the International Centre for Geohazards (ICG). NASA’s ICESat GLAS data were obtained from NSIDC, Landsat data are courtesy of NASA and USGS, and the SRTM elevation model version is courtesy of NASA JPL and was further processed by CGIAR. A number of glacier outlines were provided by GLIMS. E.B. and Y.A. acknowledge support from the Centre National d’Etudes Spatiales (CNES) through the TOSCA and ISIS programmes, from the French National Research Agency through ANR-09-CEP-005-01/PAPRIKA, and from the PNTS. J.G. was funded through CNES/CNRS.
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Assessing water resources under climate change in high-altitude catchments: a methodology and an application in the Italian Alps
Theoretical and Applied Climatology (2019)