Study on the periodic fluctuations of runoff with multi-time scales based on set pair analysis

Knowledge of the complex characteristics of runoff is required to regulate water resources. To determine the complex characteristics of runoff, the natural annual runoff data from 1956 to 2005, taken from the Zhangjiashan hydrological station on the Jinghe River, China, were decomposed into multiple time scales using the empirical mode decomposition method. The results show that the natural runoff of Jinghe River has complex periodic fluctuations with multiple time scales; the short-, middle-, and long-term periodic fluctuations have periods of 2-4, 4-8, and 11-13 years, respectively. These fluctuations are consistent with the periodic variations of El Nino, air-sea interactions, and solar activity. A set pair analysis (SPA) shows that the relationships between the natural runoff of Jinghe River and its intrinsic mode function components predominantly fall into the "identity" aspect for the short-period fluctuations, the "contrary" aspect for middle-period fluctuations, and the "discrepancy" aspect for long-period fluctuations. Moreover, the SPA reveals that the short-period runoff fluctuations can adequately reflect the average state of the Jinghe River.