Contrasting patterns of early 21st century glacier mass change in the Himalaya

International audienceGlaciers are among the best terrestrial climate indicators, an important water resource in mountains1,2 and 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. However, there are indirect evidences of a complex pattern of glacial responses5-8 in reaction to heterogeneous climate change signals9. Here, we provide the first coherent data set of detailed glacier thickness changes over the HKKH during 2003-2009 by combining satellite laser altimetry and a global elevation model. In the eastern, central and south-western parts of the HKKH, glacier wastage is widespread with regional thinning rates up to 0.66 ± 0.09 m a-1 in the Jammu-Kashmir region. Conversely, in the Karakoram, glaciers are close to balance with only a slight thinning of 0.07 ± 0.04 m a-1. Regionally averaged thinning rates under debris-mantled ice are similar to those of clean ice despite insulation by debris covers. The 2003-2008 specific mass balance for our HKKH study region is -0.21 ± 0.05 m a-1 water equivalent (WE), significantly less negative than the global average of ~ -0.7 m a-1 WE for glaciers and ice caps4,10. This difference is mainly an effect of the balanced glacier mass budget in the Karakoram. The corresponding HKKH sea level contribution is +0.035 ± 0.009 mm a-1 amounting to 1% of the present-day sea level rise11. Our 2003-2008 mass budget of -12.8 ± 3.5 Gt a-1 is more negative than recent satellite gravimetry based estimates of -5 ± 6 Gt a-1 over 2003-2010 (ref. 12). For the mountain catchments of the Indus and Ganges basins13, the glacier imbalance contributes ~3.5% and ~2.0%, respectively, to the annual average river discharge13, and up to ~10% for the Upper Indus basin14