Investigating Effects of Dynamic Debris Cover Variations on Glacio-Hydrology under Projected Climate Change in High Mountain Asia

Abstract Debris cover on glaciers in High Mountain Asia (HMA) plays a critical role in shaping glacier evolution and downstream freshwater availability. In Karakoram, glacier melt significantly influences river discharge, yet the interplay of climate change and supraglacial debris cover remains insufficiently quantified. We developed a dynamic debris cover framework using the Spatial Processes in HYdrology (SPHY) model to investigate debris-glacier interactions in the Shigar Basin, Karakoram, Pakistan. Three scenarios (no debris, static debris, process-based dynamic debris) were assessed under four CMIP6 climate projections and emission pathways (SSP-1.26 to SSP-5.85) until 2100. Debris-covered ice accounted for 11% of total glaciated area by 2020 and will expand dramatically to 39% by 2100. Neglecting debris dynamics leads to significant overestimation of glacier retreat (18–25%) and meltwater contributions (40–52%). By 2091–2100, glacier area retains 94% of its 2020 extent under dynamic debris conditions versus only 75% without debris cover. Dynamic debris mitigates mass loss, reducing glacier-derived runoff from 57% to 51% while increasing snowmelt contributions from 25% to 27%. Under SSP-5.85, debris preserves ~ 24–25% more glacier area compared to no-debris scenarios. These findings demonstrate that current glacier models systematically tend to overestimate ice loss, requiring immediate integration of debris dynamics for accurate water security assessments across HMA as nearly 2 billion people are reliant on HMA water resources. Graphical Abstract This study presents an integrated framework to evaluate supraglacial debris cover (DC) impacts on glacier hydrology under climate change in the Shigar Basin, Karakoram. Satellite imagery processed through Google Earth Engine and the GERALDINE algorithm classified debris cover using the Normalized Difference Snow Index (NDSI). Dynamic debris cover evolution framework was developed and three debris scenarios (no debris, static debris, dynamic debris) were implemented in the SPHY glacio-hydrological model, calibrated with observed data and forced with bias-corrected ERA5-Land climate data. CMIP6 climate models under four SSPs were grouped into dry-cold, dry-warm, wet-cold, and wet-warm scenarios for 2021–2100 projections. Results show debris cover will expand from 11% to 39% by 2100, with dynamic debris scenarios preventing 18–25% overestimation of glacier retreat and retaining 94% of glacier area compared to 75% without debris cover. Uncertainty analysis confirms robust model performance, highlighting the critical importance of incorporating evolving debris dynamics in glacio-hydrological projections for accurate water resource assessments across High Mountain Asia.