| As an important natural resource, water is the basic condition to support the social, economic and ecological environment for sustainable development. As one of the important links of water circulation, runoff is also an important part of water resources. Studying on the characteristics and laws of runoff can serve as a basis for the utilization, scientific management and scheduling optimization of water resources. Analyzing on the affecting factors of runoff has great significance to improve the understanding of climate change, guide the rational exploitation and utilization of watershed and maintain the ecological environment of river.The paper focus on the runoff series from 1956 to 2013 of Sihe River Basin, and it has carried on the following researches:(1) Analyze the monthly change characteristics of runoff in Sihe River Basin;(2) Analyze the inter-annual variations of runoff in Sihe River Basin;(3) Analyze the periodic change of runoff in Sihe River Basin;(4) Analyze the influencing factors of runoff in Sihe River Basin. On analyzing the change characteristics of runoff during the year, through mean monthly runoff for many years, uneven distribution coefficient during the year, completely distributive regulation coefficient, concentration, concentrated period, amplitude variation etc. are selected to study the distribution of runoff in the year. On analyzing the inter-annual variations of runoff, the linear regression, cumulative departure, smoothing mean of five years, five-spot duple smoothing, seven-spot duple smoothing, nine-spot duple smoothing and five-spot triple smoothing are selected to analyze the trend of runoff. Meanwhile, the Mann-Kendall method, Sliding t-test and Cramer method are adopted to detect breakpoints on runoff. And the wavelet analysis and the singular spectrum analysis are employed to extract and distinguish the cycle. The Pearson correlation coefficient test, statistical method and curve of double cumulate etc. are employed to analyze the impacts. Through above analysis, we can gets conclusions as following:(1)The runoff of Sihe River Basin is more in summer and less in spring, and the maximum annual runoff was usually appeared in July. In 1990 s the annual runoff distribution in the basin was uneven. Distribution of runoff in the year is relatively concentrated, and the maximum value occurs in advance. The distribution of runoff was extremely uneven, and the maximum and minimum flow months were varied considerably.(2) The runoff was decreased from 1956 to 2013, but there was a mutation in 1967. Since then the runoff was significantly decreased than before. The overall reduction trend was determined, although there was fluctuating rise.(3) The use of Morlet wavelet analysis to conduct period of runoff from 1956 to 2013, period of 2 years, 5 years, 12 years and 26 years can be obtained. But it obtained period of 5.5 years, 6.8 years, and 2.6 years by singular spectrum analysis. The two analysis methods were coherent in the short period of 2 to 3 years and 5 to 6 years. However, two methods of analyzing long period consistency was not ideal due to the restriction of sequence length.(4) A significant positive correlation was found between precipitation and runoff in Sihe River Basin. The negative correlation between air temperature and runoff was not significant. It was more prone to dry or special dry years in the year of El Nino. It was prone to wet or special wet years in the year or next year of La Nina. The runoff was generally small when there was more of sunspot number. The construction of water conservancy project, greenhouse effect and coal mining had exerted influences on the runoff of the Sihe River Basin. |
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