Characteristics of Climate Change of Precipitation and Rain Days in the Yellow River Basin during Recent 50 Years

Based on the precipitation data of 143 stations,temporal and spatial variation characteristics of precipitation and rain days in the Yellow River basin during 1961- 2010 are analyzed. The results show that:( 1) Multi-year average spatial distribution characteristics of annual precipitation and annual rainy days in the Yellow River Basin is less in the North and more in the South.( 2) Annual precipitation and annual rainy days change trend have effective consistency in the Yellow River basin during the recent 50 years,both decreasingly. And the reduction trend of the annual rain days is more significant. The percentage of stations of annual precipitation w ith negative trend is 81. 8%,and the percentage of stations of annual rainy days w ith negative trend is 88. 8%.( 3) About the seasonal variation in the Yellow River basin,the precipitation and rainy days in w inter appear positive trend w hile they present negative trends in other three seasons,especially in autumn. The negative trend stations of precipitation in four seasons passing the significance test are autumn spring summer w inter,and the negative trend stations of rain days in four seasons passing the significance test are autumn summer spring w inter.( 4) The unanimous mutation of both annual precipitation and annual rainfall in the basin is 1985- 1986,and the decrease of precipitation and rain days mainly results from the changed atmospheric circulation. For example, the above normal precipitation and rain days in 1986 are due to the stronger monsoon w hich enables the effectively conveying of vapor and the w ind convergence in the northw est. On the other hand,after the mutation,the w eaker monsoon,the lack of effective moisture transport and the anticyclonic circulation in the area from the Mongolia to Hetao may result in less precipitation and rain days.