Abstract: Located in the hinterland of east Asia and the edge of the Qinghai-Tibet Plateau, the east part of northwestern China is characterized by complex topography and various types of climate. It is a typical rain-fed agriculture area and also the most vulnerable areas in ecological environment. The complex climate makes the inter-annual precipitation show large inhomogeneity in the same period. During the growing seasons(from May to September, also the rainy seasons), the seasonal distribution characteristics of rainfall directly determine the grain yield. Therefore, it is of great importance to determine the seasonal distribution of precipitation during this time. Based on daily precipitation of 54 stations during rainy seasons from 1961 to 2013, this study analyzed the inter-seasonal distribution pattern of ten-day precipitation from May to September by using Precipitation Concentration Degree(PCD)and Precipitation Concentration Period(PCP). The results show that there were large spatial differences in the distribution of PCD and PCP. Compared with the northeast part including Ningxia, northern Shaanxi and western Inner Mongolia where the precipitation was relatively concentrating, the precipitation in the southwest part including eastern Qinghai, southern Gansu and Shaanxi was more scattering. The PCP was mainly in middle July and early August, while the PCP in Longdong region of Gansu was relatively late. The Empirical Orthogonal Function(EOF)analysis indicate that the first EOF mode of PCD and PCP in the whole east region was consistent. The second mode exhibited adverse variation characteristics between northwest and southeast, while the third mode of PCD exhibited adverse variation characteristics between northeast and southwest, and the third mode of PCP exhibited adverse variation characteristics between east and west. The trend analysis indicates that the PCP tended to scatter in the past 50 years, while the PCD tended to be earlier. In addition, positive correlations were found between the total precipitation and PCP as well as PCD, and areas of PCD significantly correlating to precipitation included western region of Inner Mongolia, northern Shaanxi and Ningxia, areas of PCP significantly correlating to precipitation included south of Shaanxi and Gansu. The prediction model based on previous atmospheric index is able to predict both the PCP and PCD, and can provide basis for the shortterm climate prediction of inter-seasonal precipitation distribution during rainy seasons in the east part of northwest China.

Key words: the east part of northwest China, rainfall, inter-seasonal, inhomogeneity