Geodetic glacier mass balance and its hydrological implications in the Upper Indus Basin: Insights into the Karakoram Anomaly

Study Region The Upper Indus River Basin (UIB) is the most vulnerable water tower in High Mountain Asia (HMA), yet its glacier-hydrology interactions remain poorly understood. Study Focus To assess the glacier imprint on streamflow trends and quantify the depletion of non-renewable meltwater, we reconstructed multi-decadal geodetic glacier mass balance ( MB Geodetic ) for 1973–2018 from KH-9 Hexagon imagery, DEMs, and d h products using a photogrammetric-geodetic approach; the resulting fluxes ( ∆ S ) were compared with discharge ( Q ) within a simplified water balance framework. New Hydrological Insights for the Region UIB glaciers remained near equilibrium (−0.06 ± 0.02 m w.e. yr −1 ) yet exhibited pronounced spatiotemporal heterogeneity. Severe ice loss persisted in the Hindu Kush and western Himalaya, where negative Δ S coupled with increasing Q indicates sustained glacier overdraft and high vulnerability. By contrast, the southern Karakoram shifted from a slight gain (+0.82 ± 0.01 Gt yr −1 ) to a moderate deficit (−0.63 ± 0.01 Gt yr −1 ) around 2000, indicating that the "Karakoram Anomaly" has weakened and its core has migrated westward. Within the Karakoram, Δ S is decoupled from runoff trends ( Δ S > 0 with increasing Q ; Δ S < 0 with decreasing Q ); streamflow variability therefore stems mainly from non-glacial sources, and vulnerability is correspondingly lower. Non-renewable ice meltwater supplied < 5% of discharge in most sub-basins, and this share fell to ~2% at the UIB outlet, suggesting that glaciers modulate rather than dominate runoff, with the Karakoram buffering glacial overdraft elsewhere.