Large glaciers sustaining the Upper Indus Basin glacier runoff in the future

Abstract

Hydrology and water resources are global concerns in basins where glacial melt contributes to water availability and are vulnerable to changes in climate and glacier dynamics. Investigating how glaciers of different dimensions respond to climate change and affect hydrological processes is crucial. This study addresses these issues in the Upper Indus Basin (UIB), which has extensive coverage of glaciers with diverse dimensions. We used a physically calibrated and evaluated Open Global Glacier Model (OGGM) model in eight sub-basins within the UIB to simulate glacier dynamics under CMIP6 climate change scenarios and investigate their dimensional effects. The average annual mass balance (MB) of the UIB was −0.16 ± 0.15 m w.e. a⁻¹, with substantial changes observed in the Zanskar sub-basin (−0.55 ± 0.11 m w.e. a⁻¹) over the last six decades. Our findings indicate that large glaciers are becoming narrower and thinner, while small glaciers are disappearing, driven by changes in their length, area, and volume. By 2100, the ice volume is projected to decrease to 60.53 % and the area to 63.26 % in the UIB. Tipping points (peak runoffs) for glacial runoff are anticipated to occur early this century for small glaciers, in the mid-century for medium-sized glaciers, and in the late century for large glaciers. Glacial runoff will increase by 132.2 % in UIB, and this increase is mediated by Karakoram sub-basins glacier runoff. Specifically, UIB small, medium, and large glaciers are expected to contribute 18.33 %, 18.84 %, and 62.82 % of the total glacier runoff, respectively. Further investigation revealed that the in Karakoram sub-basins (Hunza, Shigar, and Shyok) large glaciers contribute 52.63 % to the UIB’s total glacier runoff, while the contributions from large glaciers in the Himalayas and Hindukush are only 5.82 % and 4.37 %, respectively, in the 2090s.