Analysis of rainfall characteristics and it's tendecy in Nanxiaohegou Basin

This paper analyzed the annual precipitation,rainy days distribution characteristics and variation during 1989~2004 of Nanxiaohegou Basin,by using the precipitation tendency rate method and the Man-kendall inspection method.The results indicated that most of the precipitation occurred in May to Oct.,among them the precipitation occurring in summer accounted 50.2 % for the whole yearly rainfall,the yearly average raining days was 89 days,also the precipitation more than 1.0 mm perday was accounted 66.9 % of the yearly raining days,and the precipitation more than 10.0 mm perday was completely concentrated in May to Nov.,while more than 25 mm or 50 mm per day was mainly concentrated in May to Oct.Compared with the annual precipitation(520 mm),normal precipitation years were accounted for 38%,the unusual precipitation years accounted for 62 %.90 % of the longest drought period will be appeared in winter,but in 10 to 20 days drought might be appeared in late spring and early summer.Regarding to the yearly change,the annual precipitation and rain fall in flood season were assumed an increasing tendency in this basin,while the precipitation in drought period was decreased gradually.