Variable fuzzy analysis for the change of rainfall and runoff in Daqinghe, Haihe River basin

In recent years, the runoff of Haihe River basin has decreased significantly, especially after 1980s, due to climate change and human activities. So in this paper, a variable fuzzy method was adopted to research the variation characteristics of rainfall and runoff, and infer the main driving factors for runoff reduction. According to the parameter of the theorem and its relationship with zero, the changes of hydrological factors were divided into quantitative, gradually qualitative and mutationally qualitative. The results show that, the flood variation is micro and is just quantitative due to land use change after 1980. The variation of annual rainfall series is quantitative, while the change of corresponding annual runoff series is gradually qualitative and the average annual runoff coefficient decreases significantly. Human activities rather than precipitation change is the main factor for runoff reduction and gradually qualitative change of runoff series. The influence of human activities on annual runoff is greater than the influence on floods.