Glacier Mass Balance Trends in High-Mountain Asia Over the Past Three Decades
DOI:
https://doi.org/10.5281/zenodo.22801910Keywords:
High Mountain Asia, glacier mass balance, geodetic method, satellite gravimetry, Karakoram anomaly, digital elevation model differencing, GRACE, Himalaya-Karakoram-Tibetan PlateauAbstract
High-Mountain Asia stores more ice than any region outside the polar ice sheets, and its glaciers regulate
downstream water supply for roughly a quarter of the world's population, yet the sub-regional pattern of ice loss
across the Himalaya, Karakoram and Tibetan Plateau ranges remains unevenly characterised because the region's
extreme relief, debris cover and sparse in-situ record have historically limited direct observation. We reconstructed
glacier mass balance for eleven sub-regions of High-Mountain Asia over three intervals spanning 1991-2020 by
combining declassified Hexagon KH-9 and ASTER/WorldView stereo digital elevation model differencing with
ICESat, ICESat-2 and CryoSat-2 altimetry, cross-validated against GRACE and GRACE-FO satellite gravimetry for
the overlapping 2003-2020 window, covering 87,000 square kilometres of glacierised area drawn from the
Randolph Glacier Inventory. Region-wide mass balance was -0.19 +/- 0.06 m water equivalent per year (m w.e.
yr-1) in 1991-2000, steepening to -0.31 +/- 0.05 m w.e. yr-1 in 2000-2011 and -0.44 +/- 0.06 m w.e. yr-1 in
2011-2020, a more than doubling of the region-wide loss rate over three decades that mirrors, but lags in
magnitude, the acceleration reported for glaciers globally. This aggregate trend concealed sharp sub-regional
divergence: the eastern and central Himalaya and Nyainqentanglha lost mass at up to -0.68 m w.e. yr-1 by the final
decade, while the Karakoram and West Kunlun remained close to balance throughout, at -0.04 +/- 0.07 and +0.03
+/- 0.08 m w.e. yr-1 respectively in 2011-2020, reaffirming the Karakoram anomaly first documented two decades
ago. GRACE-derived basin-scale trends agreed with the geodetic estimates to within their combined uncertainty for
nine of eleven sub-regions but diverged over the Karakoram and West Kunlun, where gravimetric signal leakage
from adjacent, more negative catchments likely biases the coarser-resolution gravity estimate. We attribute the
persistence of the Karakoram anomaly primarily to a muted summer warming trend and sustained
winter-accumulation-dominated mass turnover, though disentangling this from debris-cover and hypsometric effects
remains an open problem that geodetic methods alone cannot resolve.
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