| Using the observed data at 104 stations in the eastern part of northwest China during 1960-2000, spatial and temporal abnormity characteristics of summer precipitation days were analyzed by the means of EOF and REOF. The results showed that the summer precipitation days is more in the west regions than the east regions, and a precipitation center lies along Qilian mountain, where the days and amount of precipitation are higher. There are two types of spatial abnormity distribution: consistent abnormity and north-south reverse abnormity. The climate region can be divided into 5 sections, i.e., the middle-east part and Hetao of Gansu, Weihe river basin, Hexi Corridor, northern Qinghai, southern Qinghai and northern Sichuan. In 1980's the precipitation days decreased gradually. The summer precipitation days is influenced by the intensity of surface heat-field in Qing-Zang Plateau in winter and summer. |