Unveiling the Future Water Pulse of Central Asia: A Comprehensive 21st Century Hydrological Forecast from Stochastic Water Balance Modeling

Abstract

Using a novel dataset, this study assesses the impact of 21st-century climate change on the hydrology of 221 high-mountain catchments in Central Asia. We employed a parsimonious, steady-state stochastic soil moisture water balance model to project changes in runoff and evaporation across three future timeframes: 2011–2040, 2041–2070, and 2071– 2100, compared to the baseline period of 1979–2011. Baseline climate data were sourced from CHELSA V21 climatology, providing daily temperature and precipitation for each subcatchment. Future projections utilized bias-corrected CMIP6 outputs from four General Circulation Models under four scenarios. Global datasets informed the spatial soil parameter distribution, and glacier imbalance ablation data were integrated to refine discharge modeling, which was validated against long-term catchment norm data. The results indicate an upward trend in precipitation (+4.5%, +5.8%, and +8.4% for the three future periods) and median temperature increases of +1.3°C, +2.4°C, and +3.6°C, respectively. Modeling results predict an initial discharge increase of +4.1% in the first period, tapering off to +1.4% by the third, with glacier wastage in the Tien Shan impacting runoff zones and reducing discharge there. In contrast, the Gissar-Alay and Pamir ranges are projected to experience discharge increases throughout the century due to delayed peak water and enhanced glacier ablation. Shifts in precipitation patterns suggest potential alterations in hydrological extremes, a topic that warrants further investigation in the region. Our findings highlight the differentiated hydrological responses to climate change within Central Asian high-mountain catchments and underscore the critical role of glaciers in future water availability, with implications for local and regional water resource management.