Human-induced flow regulation exacerbates evaporative depletion in arid endorheic basins: Evidence from stable isotopes

Human-engineered hydraulic facilities alter hydrological regimes, but their quantitative impact on surface water residence time and evaporative loss in arid regions remains unclear. This study aims to explicitly quantify these impacts in a highly regulated endorheic basin. We established a continuous stable isotope (δD and δ 18 O) observation network in the Shiyang River Basin. Using sinusoidal regression and Craig-Gordon models, we analyzed surface water retention and evaporative fractionation under a cascade of water conservation facilities. Cascading facilities severely reduced river connectivity, extending surface water residence time by 39.1%. This prolonged retention intensified kinetic isotopic fractionation, driving non-functional evaporative losses equivalent to 14.66% of the basin's total surface runoff, with losses peaking in downstream open water bodies. This “facility-induced evaporation” constitutes a massive hidden water deficit. Integrating this quantitative toll into basin-wide water accounting is essential for the sustainable management and ecological restoration of endorheic watersheds.