Flow-Complexity Analysis of the Upper Reaches of the Yangtze River, China

Abstract

Flow complexity, which means the degree of uncertainty or the rate of information production of a flow series, is analyzed for the upper reaches of the Yangtze River. Sample entropy (SampEn) is applied to measure flow complexity, and the Mann-Kendall method is applied to analyze the trend of flow-complexity change. Except for the flow complexity of the Jinsha River, which is increasing, the flow complexity of the upper reaches of the Yangtze River is decreasing. The influencing factor of the flow-complexity change is analyzed. On the basis of analysis of the rainfall complexity, which is also measured by SampEn, it is considered that the flow-complexity increase of the Jinsha River may be attributed to the rainfall-complexity increase, while the flow-complexity loss of the upper reaches of the Yangtze River may be attributed to the underlying surface-condition change influenced by human activities, especially reservoir construction. The reservoir operation makes the flow series more regular and self-similar, and leads to the flow-complexity loss.