Multi-time scale analysis of precipitation variation in Guyuan, China： 1957-2005

Morlet wavelet transformation is used in this paper to analyze the multi-time scale characteristics of precipitation data series from 1957 to 2005 in Guyuan region. The results showed that （1） the annual precipitation evolution process had obvious multi-time scale variation characteristics of 15-25 years. 7-12 years and 3-6 years, and different time scales had different oscillation energy densities; （2） the periods at smaller time scales changed more frequently, which often nested in a biggish quasi periodic oscillations, so the concrete time domain should be analyzed if necessary; （3） the precipitation had three main periods （22-year, 9-year and 4-year） and the 22-year period was especially outstanding, and the analysis of this main period reveals that the precipitation would be in a relative high water period until about 2012.