Climate Variation Characteristics of Spring Precipitation and Its Impact upon Spring Drought in Qinghai Plateau
By using of the wavelet analysis method, the variation characteristics and its time-frequency characteristics of spring precipitation in the Qinghai Plateau are studied with the spring precipitation data from 1961 to 2003 at 38 weather stations. The results show that the spring precipitation appeared an increase trend, especially in Qinghai region. In 10 years time scales, the characteristics of dry/wet vicissitude is very significant. There are 6 dry/wet vicissitude period in the recent 43 years. In 4 periods of 1961—1962, 1980—1982, 1994—1996, 1999—2000, negative phases appear in the most cycles. The same phase superimposition of the various oscillation cause heavy drought stage in spring.