Abrupt Changes of Runoff and Sediment Load in the Lower Reaches of the Yellow River, China

Determining abrupt changes in runoff and sediment load may not only enhance identification of the principal driving factors for such changes but also help establish effective countermeasures for serious water deficit by managers in the Yellow River basin. We used the Mann-Kendall trend test and linear regression to determine trends and abrupt changes of runoff and sediment load during the period between 1950 and 2005, based on monthly hydrological data. Results show that runoff and sediment load decreased from 1950 to 2005, on annual or monthly time scales. Their changes are divided into three stages: fluctuating stage (1950-1970), slowly decreasing stage (1970-1980) and accelerated decreasing stage (1980-2005). The relationship between runoff and sediment load was most significant, and it can be expressed as a linear regression function. Precipitation was one of the most important climate factors affecting runoff before 1985, and the impact of human activities on runoff decrease grew strongly after 1985. Water balance analysis of the Yellow River basin indicates that natural climate change contributed about 55.3% and human activities about 44.7% to the runoff decrease after 1986.