Background Rivers are the primary agent to provide water resources for sustaining regional economy and society development, and conveyor belts between land and ocean which transports large amount of sediment and nutrients to the oceans. The runoff and sediment load in the Yellow River basin have been dramatically altered by climate change, vegetation restoration, soil and water conservation measures and hydraulic projects during the past decades. Thus, assessing the spatial-temporal variation in runoff and sediment load and their relationship in the upper stream of the Yellow River is desirable, and may provide valuable insights of watershed management and soil and water conservation.

Methods In this study, the Mann-Kendall test, Sen's slope estimation, and BFAST model were employed to investigate the temporal trends and abrupt changes of the annual runoff and sediment load at 4 hydrological stations (including Tangnaihai, Guide, Xunhua and Lanzhou stations) in the upper stream of the Yellow River from 1956 to 2017. Then the sediment rating curves were applied to analyze the relationship of flow-sediment during different periods, and double mass curves were used to separate the impacts of climate change and human activities on the mean discharge changes and to quantify the drivers of variation of runoff and sediment load.

Results The annual runoff and sediment load presented decreasing trends from 1956 to 2017 at 4 stations, and decreasing trend in the most stations was significant (P < 0.05) except Tangnaihai station. The most dramatic decrease in annual sediment load was observed at Xunhua station. Annual average sediment load at Xunhua station in 2010—2017 accounted for 4% of that in 1956—1968. Abrupt changing points of annual runoff and sediment load occurred in 1968 and 1986, confirming the significant alternation effects of large hydraulic projects. The variation in annual runoff was more moderate, with a maximum reduction of 20%. Compared with annual runoff, annual sediment load showed extraordinarily significant reduction of 70% at Guide, Xunhua and Lanzhou stations from 1987 to 2017. The relationship between monthly runoff and sediment load in the upper stream of the Yellow River changed significantly since 1986, with significant changes in the sediment load capacity and significant reduction in the amount of sediment load. In different periods, human activities contributed > 63% and > 98 % to the reduction of runoff and sediment load, respectively.

Conclusions Human activities are the main driving factor of variation of runoff and sediment load in the upper reaches of the Yellow River basin. This indicates that large-scale soil and water conservation measures and hydraulic projects may effectively trap upstream incoming sediment and regulate the relationship between runoff and sediment load.