Most Asian Glaciers Will Deplete After Mid-Century: Linking Mass Loss to Peak Water Runoff

Glacier runoff in High Mountain Asia (HMA) is approaching peak water in many regions, with asynchronous timing across basins due to differences in glacier size, elevation, and climate forcing. Using the Open Global Glacier Model (OGGM v1.6.1), we simulate glacier mass balance (1940–2019), glacier dynamics and runoff (1940–2100) across 17 major basins, driven by bias-corrected GSWP–W5E5 historical forcing and an ensemble of 13 CMIP6 GCMs and four SSP scenarios. Small, low-elevation glaciers have already surpassed their peak runoff and are rapidly vanishing, whereas large, high-elevation glaciers continue to buffer downstream flows into the late 21st century particularly in glacier-rich basins such as the Indus and Tarim. HMA-wide glacier mass is projected to decline by 57–82% between 2001-2100, accompanied by an overall 10 ± 6.5% reduction in glacier runoff. Crucially, basin-scale hydrological shifts are not dictated by average glacier behavior, but by the composition and distribution of glacier classes. Clustering analysis reveals three distinct peak-runoff regimes, early, transitional, and delayed primarily controlled by glacier size, elevation, and regional climate. These staggered peak-runoff patterns highlight pronounced spatial heterogeneity in HMA’s hydrological response and underscore the urgency of basin-specific adaptation strategies in one of Earth’s most densely populated and climate-sensitive mountain regions.