Effects of Agricultural Large‐And Medium‐Sized Reservoirs on Hydrologic Processes in the Arid Shiyang River Basin, Northwest China

Abstract Agricultural large and medium‐sized reservoirs in arid regions increase the water stresses within local hydrologic systems, adding to pressures on aquatic ecosystems and also threatening the sustainability of water resources. Yet, there is limited research concerning how agricultural reservoirs affect the hydrology of inland river basins, which has hampered a comprehensive assessment of sustainable water use in these systems. We explore the use of stable isotopes of water to evaluate the effects of agricultural reservoirs on hydrology and the sustainable use of water in the arid Shiyang River basin. Results show that agricultural large‐ and medium‐sized reservoirs in this arid region alter local isotopic hydrologic patterns increasing water‐body evaporation and enriching the isotopic composition of water near the reservoir. As a result, evaporation losses of reservoir water can be as high as 30.7% in downstream desert reservoirs. Reservoir water also exchanges with surrounding groundwater and contributes 22% to local precipitation due to reservoir evaporation. Detailed studies of individual reservoirs show that the isotopic composition is most enriched at the surface of the reservoir and then gradually depletes toward the bottom. The cumulative effect of multiple large and medium sized reservoirs profoundly alters hydrologic processes in inland river basins, leading to an evaporation‐led water loss in these systems.