Quantifying the impacts of climate change and human activities on baseflow and direct runoff using a Budyko-based framework at annual and seasonal scales

Climate change and human activities significantly alter hydrological processes, and quantifying their respective impacts on runoff is critical for effective water resources management. However, previous studies have rarely distinguished between their effects on runoff components, particularly baseflow and direct runoff, resulting in limited understanding of their individual contributions.This study proposes a novel framework based on an extended Budyko approach to quantify the impacts of climate change and human activities on annual and seasonal variations in baseflow and direct runoff. Six representative basins across China, covering diverse climatic conditions and underlying surfaces, were selected to evaluate the framework’s performance.Results indicate that declines in direct runoff dominate total runoff reductions in the Luanhe and Dongjiang Rivers, whereas increased baseflow contributes positively to total runoff in the Ganjiang River. Human activities are identified as the primary driver of reductions in both baseflow and direct runoff in the source region of the Yellow River, Luanhe River, and Dongjiang River, accounting for 52.0–82.8 % of the total changes. In contrast, climate change exerts a greater influence on baseflow and direct runoff in the Jinghe River, upper reaches of the Huai River, and Ganjiang River, with contributions ranging from 53.6 % to 79.0 %. Across all basins, both climate change and human activities show more pronounced impacts during the rainy season than during the dry season. These findings demonstrate that the proposed framework provides an effective tool for disentangling the impacts of climate change and human activities on runoff components at multiple temporal scales.