Spatial–temporal variation and periodic change in streamflow and suspended sediment discharge along the mainstream of the Yellow River during 1950‐2013

Objectives: Under the background of global climate change, variations in stream fl ow and sediment discharge in the Yellow River would continue with intensi fi ed human activities and changes in the ecological environment. To harness the Yellow River, analyzing the degrees of change and the reasons for the stream fl ow and sediment discharge, as well as predicting the future trends, are urgently needed. Methods: In this paper, the non-parametric Mann – Kendall test, Sen's estimator of slope, Pettitt's test and wavelet transform were applied to detect the trends, the magnitude of the trends and the abrupt changes and periodic variation in stream fl ow and suspended sediment discharge at eight hydrological stations from 1950 to 2013 along the mainstream of the Yellow River. Results: Over the past 64 years (1950 – 2013), the spatial distribution of the annual average stream fl ow was of the “ M ” type, and the annual average suspended sediment discharge had a parabolic curve shape along the mainstream of the Yellow River. The temporal variation showed a distinct decreasing trend in stream fl ow since the 1990s and in suspended sediment discharge since the 1980s. Many cycles of oscillations occurred in the stream fl ow and suspended sediment discharge variation, leading to an alternate change in the wet/dry periods and the high/low sediment discharge periods. Conclusions: In various regions of the Yellow River Basin since the 1970s, climate changes contributed reductions of 17.0 – 45.0% and 12.2 – 50.3% for stream fl ow and suspended sediment discharge, respectively, whereas human activities contributed reductions of 55.0 – 83.0% and 49.7 – 87.8%. Therefore, human activities were the major causes of the signi fi cant decline in the stream fl ow and the suspended sediment discharge of the Yellow River over the past six decades. Reasonable and possible measures should be taken to achieve water resources optimization and con fi guration and to promote watershed management and sustainability in the regions of the Yellow River Basin.