Abstract: The runoff of some rivers in the world especially in the arid and semi-arid regions has decreased remarkably with global or regional climate change and intensive human activities. The runoff decrease in the arid and semi-arid areas of northern China has brought severe problems in livelihood and ecology. So, to reveal the changing characteristics, trends of runoff and their influencing factors have been an important scientific problem for drainage basin management. This study, taking the Huangfuchuan drainage basin as an example, analyzes the changing trends of the runoff and precipitation according to the measured data in 1960-2008. Two inflection points, 1979 and 1998, for the accumulative runoff, and one inflection point, 1979, for the accumulative precipitation, were identified according to the methods of accumulative anomaly analysis. The linear relationships between year and accumulative runoff in 1960-1979, 1980-1997 and 1998-2008 and between year and accumulative precipitation in 1960-1979 and 1980-2008 were fitted. Adopting the new method put forward in this study, we made a comparison of slope change ratio of the fitted beeline between year and accumulative quantity, and taking 1960-1979 as the base period, we obtained the contribution rates of the precipitation and human activities to the decreased runoff, which were 36.43% and 63.57% in 1980-1997, and 16.81% and 83.19% in 1998-2008, respectively. This study revealed the changing trend of runoff of the Huangfuchuan drainage basin during 1960-2008 and calculated the contribution ratio of the main influencing factors. It plays an important role in the drainage basin management in arid and semi-arid areas. Contemporarily, the new method of quantitative research can be applied in the quantitative evaluation of runoff change in the river basin of arid and semi-arid areas.

Key words: runoff, precipitation, variation trend, human activities, contribution rate, Huangfuchuan drainage basin