Characteristics of Precipitation Concentration Index (PCI) Variations and Monthly Distribution of Annual Precipitation in China

Seasonal variability of precipitation is an important part of the hydrological cycle, and monthly distribution of annual precipitation strongly influences agriculture and water resources. The Precipitation Concentration Index (PCI) is an effective measure of the temporal inhomogeneity of annual precipitation and is widely used in many studies. Using rain-gauge data from 583 stations in China for the period 1961-2010, this paper documents the spatial characteristics of PCIs over the entire country and their long term variability. The relationship between PCI and seasonal temperature difference is also investigated. Our results show that in the arid northwestern China, PCIs are larger than 27; in the semiarid and sub-humid regions, PCIs are 24-27 and 17-24, respectively, whereas in the humid southeastern China the values are smaller than 17. Negative trends of PCIs are found in nearly the entire country during this 50-year period, expect for the southern part of China, where PCIs show a weak decreasing trend before 2003 but a reversal afterward. In approximately 1980, an abrupt change in PCI value occurred. Over the arid/semiarid regions and the Tibetan Plateau, PCIs decreased sharply due mainly to the reduction of the contribution of summer precipitation. Over the humid regions, large regional differences are apparent. In the middle-lower reaches of the Yangtze River and South China, the contribution of summer and winter precipitation increased, whereas the contribution of spring and autumn precipitation decreased.