The Astaneh–Kuchesfahan aquifer is a strategically important groundwater resource in northern Iran that has experienced progressive depletion due to climate variability, intensive abstraction, and hydrogeological heterogeneity. This study aimed to develop and calibrate a numerical groundwater flow model to assess aquifer behavior and evaluate management responses under future climate change scenarios. A three-layer MODFLOW model was constructed using drilling logs, hydrogeological surveys, and long-term observational data from 2000 to 2020, including groundwater levels, river discharge, precipitation, temperature, evapotranspiration, and hydrogeochemical records. Model calibration and sensitivity analysis were performed by adjusting key parameters such as horizontal and vertical hydraulic conductivity, storage coefficient, effective porosity, and recharge. Future simulations were conducted under RCP2.6, RCP4.5, and RCP8.5 climate pathways combined with management scenarios including abstraction reduction, optimized water allocation, artificial recharge, and integrated measures over 5-, 10-, and 20-year periods. The calibrated model reproduced groundwater-level dynamics with high accuracy (R² = 0.87–0.96, NSE = 0.89–0.96, RMSE < 0.30 m), while hydrogeochemical trends showed over 90% conformity with observed EC and TDS patterns. Results indicate that climate change is the dominant driver of long-term groundwater decline, with projected drawdown reaching 0.95 m and water-balance deficits increasing to 26.3 MCM under RCP8.5. Among management options, the integrated scenario performed best, reducing drawdown to 0.35 m and decreasing the deficit by more than 70%. The findings demonstrate that long-term integrated management is essential to enhance aquifer resilience and ensure sustainable groundwater use under increasing climatic stress.