Impact of Climate Change and Human Activities on Runoff Variability in the Yellow River Basin: Its Responses to Multi-Year Droughts

The intensification of global climate change and human activities has made drought one of the most severe global challenges, bringing unprecedented challenges to the hydrological and water resource system. Although several studies have been conducted on hydrological droughts, few have examined the response relationship between hydrological droughts and water and energy balance. This study uses multi-year drought detection and the Budyko framework to investigate the impact of climate change and human activities on runoff changes, with a focus on the differences between drought and non-drought conditions. The results indicate that (1) the sensitivity of runoff to precipitation (εPR), potential evapotranspiration (PET) (εPET), and the watershed characteristic parameter n (εn) varies over time, initially increasing and then decreasing, and peaking between 1995 and 2006. Runoff is most sensitive to precipitation (PR) and least sensitive to potential evapotranspiration (PET). (2) The dominant contribution shifted from climate change during 1977–1985 to human activities during 1986–2014. (3) Multi-year drought in the Yellow River Basin (YRB) significantly altered n, εPR, εPET, and εn, changing from (1.50, 2.19, −1.19, −5.66) in non-drought periods to (1.84, 2.57, −1.57, −9.93) in drought periods, with greater absolute values during drought periods. (4) Compared to non-drought periods, the contribution scores of human activities (δh) are significantly higher. The growing contribution of human activities to runoff can exacerbate the occurrence of hydrological droughts.