Variation Characteristics of Sunshine Time in Changjiang River Valley in Recent 50 Years

By using the sunshine time data from 260 meteorological observation stations in Changjiang river valley from 1960 to 2009, the features of sunshine time in this area are studied. The results show that the highest sunshine time place is Qinghai-Tibet Plateau which is located in the source of the Changjiang river, and the sunshine time is about 2200-3000 h.a-1. The lowest sunshine time place is Sichuan Basin , and the sunshine time is about 1000-1600 h.a-1. The place of middle sunshine time is the midstream and down stream of Changjiang river, and the sunshine time is about 2000 h.a-1. There is a trend of decreasing with the sunshine time in zone 1, and the value is 54.2 h.10a-1. The decreasing value of zone 2 is 38.3h.10a-1. There is a trend of “rise first, down after” with sunshine time in zone 3. There is obvious seasonal difference in sunshine duration，with bigger decreasing amplitude in summer and winter than that in autumn. The variation trend of sunshine time is not obvious in spring.