Decadal Spatiotemporal Trends in Stable Isotopes and Hydrochemistry of Surface Water and Groundwater in Guanzhong Basin, China

ABSTRACT In arid regions, water scarcity poses a critical challenge to sustainable development, underscoring the need to comprehensively assess hydrological processes, hydrochemical dynamics, and their drivers under changing climatic conditions. This study aims to reveal the decadal spatiotemporal evolution of water isotopes and hydrochemical characteristics in the Guanzhong Basin, quantify long‐term variations in surface water–groundwater recharge patterns under climate change and anthropogenic water regulation, and clarify the natural and anthropogenic mechanisms governing water geochemical evolution. Results show consistent hydrochemical patterns across both surface water and groundwater, with dominant cations in the order Na + > Ca 2+ > Mg 2+ > K + and dominant anions in the order HCO 3 − > SO 4 2− > Cl − . The prevalence of HCO 3 − , SO 4 2− , Na + , and Ca 2+ reflects combined controls of rock weathering and evaporation–crystallization processes, with Gibbs diagrams confirming mineral weathering as the primary mechanism governing water chemistry. Groundwater samples were predominantly of the HCO 3 –Ca•Mg type, whereas surface water showed more diverse hydrochemical facies, including SO 4 •Cl–Ca•Mg and HCO 3 –Na types. A shift from Cl − dominance in 2014 to HCO 3 − dominance in 2024 indicates enhanced weathering processes. Stable isotope analyses (δ 18 O, δ 2 H) reveal a transition from arid conditions toward increased humidity in 2024, whereas rising d‐excess values suggest expanded recharge sources and recycled moisture contributions. Isotopic evidence indicates a marked reversal in recharge dynamics: Surface water predominantly recharged groundwater in 2014 (56.76%), whereas groundwater became the dominant contributor to surface water in 2024 (90.87%), particularly in the midstream basin. Although carbonate and silicate weathering remain the principal hydrochemical controls, increasing anthropogenic activities and climatic pressures are reshaping groundwater geochemistry. These findings highlight the necessity of integrated water resource management and provide valuable insights for semiarid basins facing similar hydrological transitions.