Quantifying the Hydrological Impact of Ecological and Water Conservation Projects Within a Major Tributary Basin of the Middle Reaches of the Yellow River, China

ABSTRACT Anthropogenic activities, particularly ecological and water conservancy projects, have profoundly altered land surfaces. However, quantifying their basin‐scale hydrological impacts remains challenging. This study focused on the Qin River Basin (QRB), a major tributary in the ecologically sensitive middle reaches of the Yellow River where such projects are extensively implemented. Employing the Soil and Water Assessment Tool (SWAT) model, we quantified the impacts of the Returning Agricultural Land to Forest (RAF) and Returning Agricultural Land to River (RAR) projects on QRB hydrological processes from 2010 to 2018. Results indicated that the SWAT model performed robustly with Nash‐Sutcliffe efficiency coefficients ( NSE ) of 0.70 to 0.72, determination coefficients ( R 2 ) of 0.71 to 0.79 and percent bias ( PBIAS ) below 11%. RAF implementation reduced total basin runoff by 3.00%, driven by increased surface runoff up to 3.89%, decreased lateral flow by 11.46%, and significantly increased groundwater flow by 2366.67%. Spatially, surface runoff increases concentrated in the northern basin and eastern tributaries, while lateral flow reductions were most severe in central regions. For RAR projects, hydrological responses scaled positively with agricultural‐to‐waterbody conversion area, showing 2.5‐fold greater efficacy on slopes under 15° versus under 6°. Basin‐wide runoff components increased proportionally to buffer width expansion, though spatial tradeoffs emerged: upper reaches exhibited surface runoff reduction from 1.29% to 21.74%, while lower reaches experienced groundwater depletion from 1.99% to 36.96% decrease. These findings highlight that spatial planning informed by slope conditions is vital for effective water resource management in semi‐humid basins under intensive anthropogenic intervention.