Attributing Runoff and Non‐Point Source Pollution Changes to Climate and Human Drivers in the Weihe River Basin, China

Abstract Climate change and human activities jointly affect runoff generation and non‐point source pollutant transport in river basins. Quantifying their relative roles is essential for explaining pollutant‐load changes and informing water resources management. Here, this study developed an integrated framework combining Budyko runoff attribution, Soil and Water Assessment Tool hydrological and water‐quality simulations, dynamic time warping distance, and gray water footprint (GWF) assessment. We applied this framework to the Wei River Basin, China. Based on an abrupt precipitation change, 2001–2009 was defined as the reference period and 2010–2020 as the impact period. The contributions of precipitation, potential evapotranspiration, and basin‐characteristic parameters to runoff change were decomposed, and climate‐driven changes in ammonia nitrogen (NH 3 –N) loads and GWF were simulated under fixed land use and agricultural management. Results show that precipitation increased after 2009, but runoff responses, pollutant loads, and GWF showed pronounced spatial heterogeneity. Runoff changes in WuShan, YangJiaPing, and HeiYuKou were mainly controlled by meteorological drivers, whereas HuXian, JingCun, ZhuangTou, and MaDuWang were more strongly influenced by basin characteristics. During the impact period, multi‐year mean NH 3 –N load and GWF increased in most subbasins except ZhuangTou, but were not always synchronized with runoff changes. Subbasins were classified as high‐load background areas, meteorologically sensitive areas, and asynchronous water quantity‐water quality response areas. These findings indicate that increased runoff does not necessarily alleviate water resources pressure under pollution constraints, highlighting the need to jointly evaluate water quantity, pollution‐source background, and pollutant transport processes.