| In ording to reveal the characteristic of time variation and spatial distribution of precipitation during recent years in Loess Plateau, based on the 52 years daily precipitation data from 1961 to 2012 in the Loess Plateau Region and surrounding 72 meteorological stations, the Tyson polygon method was applied to distribute the precipitation in each rainfall station to whole region.The M-K trend test method was adopted to analyze the characteristics of yearly precipitation temporal and spatial variation. The results showed that: (1) The annual rainfall in Loess Plateau has showed a trend of slow decline with time, UFK curve was less than zero and not exceeded the confidence line. In space whole showed a decline trend and appeared two significant reduction centers as Yangquan and Yushe Stations, the β value was -3.3 mm·10a-1 and -2.1 mm·10a-1, respectively. (2) The multi-year average rainfall in Spring of the Loess Plateau has showed no obvious decline trend on the whole. The precipitation from 1966 to 1987 and 1961 to 1963 has showed a decrease trend; but from 1963 to 1966 and 1987 to 2012 has showed an increase trend. In space most of the west and north region has showed an increase trend. The Wutai Mountain was the maximal increase range, the β value was 2 mm·10a-1. (3) The multi-year average rainfall in Summer has showed an obvious downward trend, around 2008 was the mutation point, after 2008 the precipitation has notablely decreased. In space has showed a decline trend on the whole, rather obvious decrease centers were Huanxian, Yan'an, Xifeng, Pingliang and Linfen, the β value was -0.9,-0.9,-0.8,-0.8 mm·10a-1 and -0.8 mm·10a-1, respectively. (4) The multi-year average precipitatio in Autumn has showed a notable decrease trend, the space change was similar with Summer, the decrease centers still was the Huanxian, Yan'an, Xifeng, Pingliang and Linfen. The β value total was -0.8 mm·10a-1. (5) The multi-year average rainfall in Winter was showed an obvious rising trend on the whole, the changes slowed a slowly rising trend on the space, the largest rise center was Huashan, the β value was only 0.95 mm·10a-1. |