Contrasting roles of human water use in soil and hydrological drought propagation in the mid-upper Huaihe River Basin

Study region The mid-upper Huaihe River Basin (MU-HRB) in China is a region characterized by strong climate variability and intensive human water use. Study focus This study examines how irrigation and reservoir regulation influence drought propagation (DP) from meteorological drought (MD) to soil drought (SD) and hydrological drought (HD) over the MU-HRB. The newly developed Conjunctive Surface Subsurface Process model version 3 (CSSPv3) with explicit representation of irrigation water source constraints, is applied to quantify the impacts of human water use on DP. The CSSPv3 model outperforms global hydrological models in terms of streamflow and soil moisture simulations over the MU-HRB. New hydrological insights for the region Human water use alters DP by modifying both pathways and thresholds. Irrigation suppresses SD, reducing its frequency by 58.8% and prolonging propagation time by 101.7%, while intensifying HD, increasing its frequency by 48.6% and accelerating propagation from MD. Reservoir regulation partly offsets streamflow depletion but does not reverse the enhanced propagation toward HD. Consequently, propagation shifts from pathways toward SD to HD. Human water use weakens the propagation of low severity MD events to SD, while lowering the threshold for propagation to HD, indicating increased sensitivity of streamflow systems. These effects are strongest in sub-basins with intensive human water use, particularly in the Huaibin-Bengbu region, and are driven by soil moisture replenishment, enhanced evapotranspiration, and streamflow depletion.