Two decades of glacier slowdown driven by mass loss in High Mountain Asia
Amaury Dehecq  1, *@  , Noel Gourmelen  2@  , Alex Gardner  1@  , Fanny Brun  3@  
1 : NASA Jet Propulsion Laboratory, California Institute of Technology
2 : School of GeoSciences, University of Edinburgh
3 : Institut des Geosciences de l'Environnement
Université Grenoble Alpes
* : Corresponding author

Glaciers in High Mountain Asia have thinned over the past decades with regionally-contrasted rates of loss. However, the associated changes in ice flow that drive mass redistribution and modify the glaciers sensitivity to climate are poorly constrained. Here we resolve changes in ice flow for glaciers in High Mountain Asia for 53% of the regions glacierized area (95,000 km2), over the period 2000-2017, from feature-tracking of a million optical satellite images. A thorough consideration of uncertainties and propagation as well as identified biases between the Landsat missions were necessary to resolve velocity trends less than a few meters per year per decade.

Of the eleven regions surveyed, nine experience sustained glacier slowdown concomitant with ice thinning. The Karakoram and Kunlun regions show stable and slightly accelerated glacier flow associated with stable or thickening conditions. Comparison with observed changes in glacier thickness show that up to 94% of the inter-regional variability in velocity change can be explained by changes in gravitational driving stress. This result suggests that, despite the complexities of individual glacier behaviour, the regional dynamic response of glaciers to external environmental forcing can be well represented with a simple parameterisation, providing critical information for models attempting to project the glacier contribution to water resources and sea level change.

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