Abstract: China's Loess Plateau suffers from severe water shortages.Quantitative analysis of the effects of climate change and human activities on runoff is important for water resource management.Taking Fenhe River Basin as the study area,the runoff data at the Hejin Station which controls Fenhe River Basin's flow into the Yellow River from 1956 to 2012 was analyzed using the hydrological variation diagnosis system.The result showed that the runoff into the Yellow River had a significant downward trend and it took a dive in about 1971.The influencing factors that caused the dramatic reduction of the runoff was then investigated using the multivariate analysis method and it revealed that the runoff was affected by precipitation,potential evapotranspiration and the change of watershed attributes resulted from human activities.The sensitivity of each factor was further analyzed with Budyko formula which drew a conclusion that in a relatively long time period,the runoff variation was more sensitive to the climate change than human activities.At last,the impact ratio of these factors was calculated using the cumulative slope method and the values for the precipitation,the potential evapotranspiration and the change of basin attribute were 16.29%,-4.86% and 88.57% respectively.

Key words: Fenhe River Basin, variation trend diagnosis, analysis of influencing factors of runoff, change sensitivity analysis, impact ratio analysis