Runoff characteristics of the Nen River Basin and its cause

Based on annual runoff data collected from several hydrological stations in the Nen River Basin from 1956 to 2004, the cumulative filter method, Mann-Kendall method and Morlet wavelet analysis were used to analyze variations in the characteristics and factors influencing runoff. Specifically, the general characteristics list as: The distribution of runoff was found to be uneven within a year, and the annual variation showed an overall decreasing trend. The abrupt change points of runoff were found to be in the early 1960s, middle 1980s and late 1990s. Multiple time scales analysis revealed three time-scale cycles, a long-term cycle of about 20–35 years with a scale center of 25 years, another cycle of about 8–15 years with a scale center of 11 years and a short-term cycle of about 5 years. Based on the Morlet wavelet transform coefficients figure of the 25-year time scale, it is preliminarily estimated that the Nen River Basin will enter a high flow period in 2013. The results obtained using various methods were consistent with each other. The physical causes of the results were also analyzed to confirm their accuracy.