Diagnose of precipitation evolution trend in China and new facts

Using dynamic segmentation and the Thiessen polygon method, precipitation amounts can be estimated for different spatial and temporal resolutions over the period 1951-2006. The resulting monthly, seasonal, flooding season and annual time series for both regional and national average precipitation are then analyzed. The spatial distributions, regional characteristics, variabilities, trends, abrupt changes, oscillation periods of monthly, flooding season and annual precipitation are examined. The temporal analysis is done for the three periods 1961-2006, 1980-2006 and 1961-1979, which represents the precipitation variabilities in long term, recent years and earlier term (or baseline). Compared to the earlier term values, the result shows that a recent southward trend is detected in the 600 mm of annual precipitation isoline in Bohai Bay. The annual amount of precipitation is on the rise recently in the west area of 110° E. The mean annual precipitation is down 10% in the mid-western part of Inner Mongolia, the coastal areas of the Haihe River, the middle part of the Yellow River and the northern part of the Huaihe River. In contrast, the mean annual precipitation is up 10% in the middle part of the Nenjiang River, the lower reach region of the Yangtse River, the coastal areas of South Fujian, the mid-northern part of Tibet and the middle part of Xinjiang. In particular, the mean annual precipitation is up 30% in the area of the Talimu River and the upper reach region of the Yili River.