Analysis on Spatial-temporal Variation Characteristics of the Precipitation in Four Provinces of Northwest China

[ Objective] The research aimed to analyze temporal-spatial change characteristics of the precipitation in the four provinces of northwest China. [Method] Based on precipitation data at 113 ground observation stations in the four provinces （Shaanxi, Gansu, Qinghai and Ningxia） of northwest China from 1961 to 2008, by using linear regression and Morlet wavelet transformation, spatial pattern, change trend and periodic charac- teristics of the precipitation in the zone in 48 years were analyzed. [ Result] Rainfall in the four provinces of northwest China had obvious interannual and seasonal change characteristics. Annual, spring and autumn rainfalls all presented decline trends. Summer and winter rainfalls both had slight increase trends, but change trend wasn＇t obvious. Precipitation change in the four provinces of northwest China had obvious regional difference. In- crease amplitudes in Tanggula Mountains, Tsaidam Basin and east Qilian Mountains were obvious. Obvious decrease amplitude existed in east Gansu, south and north Shaanxi. Precipitation in east and west areas of the four provinces in northwest China presented reverse phase change characteristics. Precipitation presented decrease trend in east and increase trend in most areas of west. Precipitation in the whole district, east dis- trict and west district generally had 3-5-year short period, which was main period. Precipitation also had 8-year and t5-year medium periods in some areas. Under different time scales, dry-wet alternation and mutation point had difference. [ Conclusion] The research provided theoretical basis for studying climate change in northwest China.