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Abstract

The multi-methods were used to analyze the factors affecting the change of water and sediment, and the contribution rate of human activities and climate change to the impact of water and sediment using the data of water and sediment and remote sensing images from five hydrological stations in the upper reaches of the Yellow River from 1964 to 2019. Both runoff and sediment load in the upper reaches of the mainstem Yellow River showed a decreasing trend, with a small decrease in runoff and a significant decrease in sand transport in the last decade. The multi-year average sand transport at Guide, Xunhua and Xiaochuan stations greatly reduced. The runoff of the upper Yellow River changed significantly since 1986, and the sediment load were mostly changed significantly in 1969, 1986 and 2004, which coincide with the operation time of the large cascade reservoirs. Moreover, there is a cyclical pattern of runoff and sediment load in the upper reaches of the Yellow River, with 8a, 16a, 22a and 36a cycles in runoff and 4-8a, 18-21a, 27a and 35-39a cycles in sediment load. The construction of cascade reservoirs had an impact on the peak flood pattern, which reduced the annual runoff by 36% in the five years before and after the construction of Longyangxia Reservoir and Lijiaxia Reservoir. In general, water and sediment in the upper reaches of the Yellow River were affected by cascade reservoir construction, conversion of farmland to grassland and climate change.