Responses of runoff to climatic variation and human activities in the Fenhe River, China

The Fenhe River is the second largest tributary of the Yellow River in China. Climatic variation and human activities have impacted the runoff significantly in the Fenhe River in recent decades. In this study, the runoff trend from 1957 to 2010 was analyzed and the impacts of climatic variation and human activities on runoff were attributed by the climate elasticity method and hydrological modeling method. The observed annual runoff decreased significantly (P < 0.05) during the past 54 years in the Fenhe River basin. A change point was identified around the year 1979 for the annual runoff series by the Mann-Kendall test. The observed average annual runoff in the Period II (from 1980 to 2010) decreased by 24.94 mm compared with the Period I (from 1957 to 1979). The attribution results show that the average annual amount of water diversion from the river in the Period II increased significantly by 7.88 mm compared with the Period I, accounting for 31.6 % of the total decrease in the observed annual runoff. In addition, other human activities such as land use and cover change led to the decrease in annual runoff by 6.31 mm from the climate elasticity method and 6.92 mm from the hydrological modeling method, which accounting for 23.8 and 27.7 % of the total decrease in the observed annual runoff, respectively. Therefore, human activities together were responsible for 55.4 % of the total observed runoff reduction estimated by the climate elasticity method and for 59.3 % estimated by the hydrological modeling method. Climatic variation such as changes in precipitation and evapotranspiration led to the decrease in runoff by 10.14 and 10.75 mm from the two methods, accounting for 40.7 and 44.6 % of the total observed runoff reduction. Therefore, human activities were the main driving factor for the runoff decrease in the Fenhe River basin.