CONICET | Buscador de Institutos y Recursos Humanos

Glaciers are important sources of fresh water in particular for the arid lowlands surrounding High Mountain Asia (HMA). However, glaciers are shrinking and losing mass at an on average accelerated rate. There is strong heterogeneity of mass loss with glaciers in the Western Kunlun, Eastern Pamir and Central Karakoram glaciers having lost only little mass. But even in these regions mass loss is now prevailing. Previous studies have shown that the heterogeneity may be caused by different climatic and accumulation regimes, debris cover, glacial lakes and glacier surging. Within this project we used multi-source satellite data to investigate the glacier changes and its causes in entire HMA in general and in some specific regions in detail.Frist, we propose a new index entirely based on glacier surface wet snow and firn observations from Sentinel-1 to characterizes the accumulation type. The index is based on the assumption that for summer-accumulation-type glaciers wet snow area ratio is high (normally higher than firn area ratio) in summer during frequent SAR observation, or it is prone to be winter-accumulation type. We show that this index is a powerful indicator of accumulation type and correlates well with specific glacier mass balance (i.e. mass change per unit area). We find that the glaciers in the subregions which accumulate mainly from winter snow are close to equilibrium, while the glacier subregions which mainly accumulate in summer are substantially losing mass.Then, we used different stereo satellite data including ASTER, SPOT and Pléiades data to assess the mass balance variability and trends in various subregions with different accumulation conditions since about 2000. We found accelerated mass loss in all regions with the highest mass loss in the Langtang valley in Central Himalaya (which is of transitional accumulation type) and western Nyainqêntanglha (summer-accumulation type) with mass loss rates after 2000 between about -0.4 to 0.5 m w.e. a-1. Glaciers in Muztagh Ata in Eastern Pamir, which are of winter-accumulation type, showed on average balanced mass budgets. But even there mass loss prevailed in recent years. Finally, we investigated the potential of very-high resolution Pléiades data for to measure glacier-wide mass balance at annual and seasonal scales in the two contrasting regions western Nyainqêntanglha and Muztagh Ata. Annual mass balance in the Muztagh Ata massif between 2019-2020 and 2020-2021 were again negative (-0.24 ±0.19 m w.e. a-1 and +0.17 ±0.35 m w.e. a-1, respectively). The 2022 winter (+0.17 ±0.64 m w.e. a-1) balance provides provisional evidence for a winter accumulation regime, though mass balance uncertainties remain high in some cases due to the short temporal baseline. On the contrary, annual mass balances in the Western Nyainqentanglha Range for similar periods show highly negative conditions (-0.87 ±0.22 m w.e. a-1 and -0.52 ±0.11 m w.e. a-1), suggesting much higher mass losses after the year 2019 compared to the previous six decades. With some limitations due to the high uncertainty, the winter (-0.05 ±0.70 m w.e. a-1) mass balance estimate does not show any mass recovery.Future work will focus on combining seasonal snow-line observations derived from Sentinel-1 and -2, with geodetic mass balance derived from the high-resolution data, ICESat-2 and velocity calculations to further improve the understanding of the mass balance heterogeneity and its drivers.

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