Diagnosis of Change in Structural Characteristics of Streamflow Series Based on Selection of Complexity Measurement Methods: Fenhe River Basin, China

Abstract

The analysis of the effects of human activities and climate variability on the structural characteristics of streamflow series facilitates further exploring the regularity of streamflow change and revealing the process of hydrological cycle response. The principal goal of this study is to establish an analysis system to diagnose the change in structural characteristics of streamflow series via employing suitable complexity measurement methods for specific cases. Meanwhile, an application scope table has been built based on testing and comparing the logicality and antinoise robustness through using logistic mapping series, random series, white noise, and 1/f noise for five commonly used complexity measurement methods (approximate entropy, permutation entropy, sample entropy, fractal, and Lempel-Ziv). According to the application scope table, sample entropy is the most suitable method for this specific case. Moreover, the results illustrate that in the prechange period, the complexity of the streamflow series is 0.5176; in the postchange period, the complexity value is 0.3722 if the streamflow is only impacted by climate variability; and its value is 0.2571 if it is impacted by both human activities and climate variability. Climate variability reduces the complexity of streamflow series, and human activities intensify this reduction. A decrease of complexity indicates that the streamflow series becomes more stable and regular.