Scenario-Based Assessment and Modeling in the Ili–Balkhash River Basin

Water scarcity in transboundary river basins is increasingly driven by interacting climatic, hydrological, and anthropogenic pressures. The Ili–Balkhash River Basin, a vulnerable endorheic system in Central Asia, is particularly sensitive to changes in transboundary Ili River inflow, which directly affects downstream water availability and the hydrological condition of Lake Balkhash. Although previous studies have advanced understanding of basin hydrology, the combined effects of multiple drivers and associated uncertainties remain insufficiently assessed within integrated scenario-based frameworks. This study develops a dynamic–stochastic modeling framework for assessing future water availability, allocation, and system response through 2050. Historical hydrological observations, climate conditions, sectoral water demand, transboundary inflow, reservoir operation, and management assumptions are combined within a unified simulation environment. Four transboundary-inflow stress scenarios (S1–S4) are evaluated through 2050. Stochastic hydrological simulations represent runoff variability, while the scenarios impose progressively stronger levels of transboundary-inflow stress. Scenario comparison shows a progressive deterioration from comparatively resilient conditions under S1 to increasing water stress under S2 and S3 and persistent system-wide scarcity under S4. Transboundary Ili River inflow emerges as the principal quantitatively perturbed driver of basin performance, while water demand, evaporative losses, and reservoir regulation provide contextual controls on system response. Increasing inflow stress is associated with greater pressure on sectoral water availability, environmental flows to the Ili Delta, and inflow to Lake Balkhash. The results indicate that basin vulnerability is strongly influenced by transboundary water availability and its interaction with water-management conditions. The findings also highlight the potential importance of water-management efficiency, environmental-flow protection, and transboundary water management. The framework provides a basis for comparing alternative transboundary-inflow conditions under uncertainty and supporting long-term water-resource planning in the Ili–Balkhash Basin.