Climate change and human activities amplify runoff variability risks in lower reaches of large rivers

The contributions of climate change and human activities to runoff variation have been examined in multiple individual catchments, but upstream-downstream interaction relationships remain underexplored. Here, we propose a three-tiered attribution framework to investigate the spatiotemporal patterns, underlying drivers, and upstream-downstream relationships of runoff variations in the Yellow River Basin (1952-2021). The results indicate that the longitudinal cumulative effects of climatic (ranging from -8.6%upstream to 7.1% downstream relative to the whole basin) and anthropogenic disturbance (15.2%-92.9%) factors lead to higher risks of runoff variations in downstream regions, with more significant seasonal fluctuations (particularly in reservoir-regulated reaches). Glaciers, lakes, and reservoirs’ storage capacities cause lagged effects of climate change and human activities on runoff variations, while simultaneously serving as critical drivers for inter-basin water resource regulation. Integrating comprehensive understanding of multi-scale hydrological variability drivers and spatial interaction mechanisms is essential for advancing adaptive river basin management and sustainable water resources allocation.