Climate Sensitivity of River Runoff in the Shu–Talas Basin: A Scenario-Based Assessment

Changes in climatic conditions are accompanied by a transformation of river runoff formation processes, while the direction and intensity of the hydrological response can differ significantly even between geographically adjacent river basins. The study aimed to conduct a comparative evaluation of the climate sensitivity of river runoff for six main rivers in the Shu–Talas water management basin to changes in air temperature and atmospheric precipitation. The study was based on long-term time series of monthly mean water discharge, air temperature, and atmospheric precipitation using correlation, lag, regression, and scenario analyses. Scenario modeling was performed for air temperature changes ranging from +0.5 °C to +3.0 °C and atmospheric precipitation changes from −30% to +30%. A pronounced spatial and seasonal heterogeneity of the climate response of the studied rivers was identified. Under the combination of ΔT = 3 °C and ΔP = +30%, the average relative change in calculated river runoff ranges from +2% for the Teris River to +49% for the Merke River. Under the combination of ΔT = 3 °C and ΔP = −30%, the most substantial decrease in average calculated river runoff was obtained for the Merke River (−43%), the Teris River (−40%), and the Koragaty River (−34%). Seasonal analysis revealed a significantly larger response amplitude in individual months. The maximum positive change reaches +93% for the Merke River in November and +52% for the Yrgayty River in October. For quantitative inter-basin comparison, integral climate sensitivity coefficients εT and εP were proposed. The highest absolute temperature sensitivity was established for the Teris River (εT = −6.31%Q/°C) and the Talas River (εT = +4.54%Q/°C). The maximum sensitivity to changes in atmospheric precipitation is characteristic of the Merke River (εP = 1.54% Q/1% P). These scenarios constitute a standardized climate sensitivity experiment designed for inter-basin comparison and should not be interpreted as projections of specific future changes in river discharge. The results reveal substantial inter-basin and intra-annual differences in the statistical sensitivity of river discharge to air temperature and precipitation, providing a comparative basis for identifying priority basins and seasons for further hydrological modeling and for informing the development of water management adaptation measures in the Shu–Talas basin.