The Spatial and Temporal Structure of Precipitation in the Yellow River Basin
黄河流域上游降水时空结构特征

The Yellow River Basin is located in the semi-arid and semi-humid region in China, and there is 200~600 mm annual precipitation and 58 billions annual runoff. The basin is with seriously scarce water resources in China, even less in the world.The region upwards of Lanzhou has area of 222 552 km2, with 446 mm annual precipitation, 319 mm flood season precipitation and 127 mm non-flood season precipitation. But its runoff accounts for 57.5% of the runoff in the Yellow River. So the spatial and temporal changes of water resources in the region upwards of Lanzhou should have great impacts on water resources of whole basin. It is important to research the spatial and temporal structure of precipitation in the region upwards of Lanzhou.It is known that, climatic system has some typical characteristics of multi-scales space-time, multi-hierarchy structure and non-linearity nature, and that the relationships and actions among different hierarchies are intricate. In this paper, with 1959~1998 precipitation series at 19 precipitation stations of the region upwards of Lanzhou in the Yellow River basin, the spatial and temporal structure features and changes of precipitation are analyzed with Empirical Orthogonal Function (EOF) method. The results show that: (1) there are four types precipitation structures in the region, and they are "All- Consistency", "North-South", "West-East" and "Complex type"; (2)the first eigenvector is the dominant type, and its accumulation contribution rate is 42.10%. Its time coefficient has same change as precipitation. This shows that the precipitation in the region upwards of Lanzhou is controlled by large-scale climatic system of Qing-Zang Plateau and the precipitation has more or less consistency; (3) from time scale, the precipitation has downwards change with 3, 6, and 11 year periods, with two abrupt points happening in 1986 and 1991.