Hydrological and dynamical response of glaciers to climate change based on their dimensions in the Hunza Basin, Karakoram

Abstract

Glaciers of different dimensions respond differently to climate change, resulting in variations in glacier dynamics and runoff. Differentiation of these responses is critical for the Karakoram region (in context to Karakoram anomalies) where glaciers contribute significantly to runoff. Herein, the Open Global Glacier Model is used to quantify these variabilities in the Hunza basin, and thereby develop a comprehensive understanding of how glaciers respond to past and future climate change. Basin glaciers were classified into six classes based on their terminus elevation and area (Z1-Z6). Annual mass balance (MB) time series were reconstructed from 1960 to 2019. The results indicate that the average MB is −0.09 ± 0.21 m w.e.a−1, which has been accelerated in 2000 s (average: −0.16 ± 0.20 m w.e.a−1). Cumulative MB between classes varies from −4.55 m w.e. (Z1) to −5.92 m w.e. (Z3), indicating that the medium classes (Z3, Z4) glaciers MB is comparatively more negative. Monthly glacier runoff explains the sensitivity of small glaciers to summer temperature, as they only contribute to runoff in the summer season. However, glacier runoff per unit area per year remains almost the same across these groups. Future climate change scenarios under CMIP6 illustrate that small (Z5/Z6) and large (Z1) glaciers will lose up to 90 % and 10 % of their volume, area, and length, respectively. The results identified that basin glacier runoff will increase till the year 2060 and will start decreasing after that to 2100. Projected glacier runoff suggests that the Basin runoff is mediated by Z4 glaciers. Whereas, the peak water supply from small size glaciers has occurred in past (Z6) or would occur in near future (Z5) while large size glaciers (Z1-Z3) runoff keeps on increasing till 2100. These findings indicate that immediate mitigation measures are required to deal with glacier change and ensure long-term water security in this region.