The trend of base flow in Wei River Basin based on R/S and Mann-Kendall method

River base flow is defined of the amount of groundwater recharging river runoff. Base flow index is the ratio of base flow and runoff. in Wei River Basin, the annual average base flow index was 0.475. We can see that the base flow plays an important role in the runoff formation, maintenance and regeneration process. Studying Wei River Basin base flow trends characteristics is of great significance for the policies of water resources sustainable development and ecological environmental protection. This paper selects base flow data of Huaxian station in Wei River Basin from 1935 to 2005 and analyzes base flow change trend during the past 70 years and future tend based on R/S(rescaled range analysis) and Mann-Kendall, The calculation shows:(1)The base flow in Wei River basin has been decreased since 1935. (2)In the future it will continue to maintain downward trend.