Reassessing Future Runoff Changes in the Ala-Archa Basin, Central Asia

Central Asia is a global climate-change hotspot where future water availability remains uncertain, as hydrological forcing data are ambiguous and observations provide limited constraints on model parameters. We reassessed future runoff changes in the glacierized Ala-Archa basin by reducing model equifinality with a multi-objective calibration strategy that explicitly incorporates winter low-flow runoff, total runoff, snow cover fraction, and glacier mass balance. The calibrated model was used to project annual and seasonal river discharge under four Shared Socioeconomic Pathways. Results indicate a transition from a nival–glacial to a more pluvial-driven runoff regime. Rising temperatures advance the melt season, increase the proportion of liquid precipitation, and shift peak runoff from July to June. Although glacier and snowmelt contributions decline substantially as cryospheric storage shrinks, total annual runoff decreases only modestly by the late 21st century. This muted annual response reflects compensating effects from increased rainfall and a sustained rise in summer baseflow. Improved low-flow calibration suggests that increased groundwater recharge can partly offset meltwater losses, leading to a less severe summer discharge reduction than previously reported. Neglecting low-flow constraints may therefore overestimate future water scarcity in glacier-fed catchments.