The Evolutionary Law of Autumn Rain in the Three Gorges Reservoir Area
2000, 55 (s1):
Based on the data of daily precipitation from October to November from 1960 to 1996 at 28 stations including Yichang, Wufeng, Lvchongpo, Enshi, Fengjie, Wanxian, Liangping, Fuling, Chongqing, Daxian, Liangzhong, Mianyang, Chengdu, Doujiangyan, Yaan, Emeishan, Leshan, Leibo, Yibin, Nanchong, Shuining, Neijiang, Luzhou, Xuyong, Jinfoshan, Tongzi, Zunyi, Sinan in the Three Gorges reservoir area, the status of autumn rain was analyzed and the evolutionary law was studied. The results showed that autumn rain mainly concentrated from early October to early November during the river closure period in the Three Gorges dam area. The main conclusion were as follows: (1) Mean rain days during October --November are 25 ~ 30days. Particularly, rain days are 30-38 days in western and southwestern plateau of Sicuan Province. And the most area with 45 rain days is Emei Mount. Though the rain days are abundant, the total Precipitation amount is small which is less than that in summer and the intensity is weak. The largest rainfall area with precipitation of 242 mm locates in Lvchongpo. (2) Rain frequency during October~November is decreasing. And there is one thing to be mentioned that the frequency of serious autumn rain is as lower as 10% in dam area of the three Gorges. (3) From the viewpoint of the distribution of autumn rain frequency, it is smaller in western reservoir area of the three Gorges than in eastern part, and it is much frequent in southern part than in northern part. The lowest area is center northern part and the most frequent area is center western part. (4) There is 21 years with serious and normal autumn rain with the frequency of 56. 8% during 1960--1996. Yearly, autumn rain is evident every year in 1960s and every2 year in 1970s. And it is not evident in 1980s. While in 1990s it alternates between the evident year and not evident year. (5) In addition, the features of autumn rain in 1994 and in 1996 are analyzed in this paper due to the evident autumn rain occurrence.
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