Attribution of runoff changes in the main tributaries of the middle Yellow River, China, based on the Budyko model with a time-varying parameter

Discerning the controlling factors of spatial and temporal changes in runoff is critical for water resources management. This study investigated runoff changes and related them to climate change and human activities in 14 sub-catchments of the middle Yellow River basin, China. The spatio-temporal variations in contributions of factors to runoff change were examined using a Budyko-based framework with a time-varying catchment characteristic parameter n in a 9-year moving window and by a comparison of northern and southern sub�catchments. The results show that runoff changes induced by climate change had an increasing trend firstly and then gradually decreased over the period 1982–2015, whereas human activities associated with soil and water conservation measures had a greater impact in the northern parts of the study area. We found that the parameter n in Choudhury-Yang’s equation is significantly correlated to climatic and artificial factors. The in�fluence of climatic factors on runoff includes changes both in hydrological inputs and catchment characteristics while the impacts of artificial factors are mainly achieved by the alteration of catchment characteristics. In addition to vegetation cover, the engineering measures for soil and water conservation, mainly including terraces and check-dams, played an important role in runoff reduction in the middle Yellow River basin. Inclusion of such features is therefore important when undertaking runoff attribution analysis.