Abstract: The Dagu River is the largest river in the Jiaodong Peninsula, and it is called as the mother river of Qingdao City. Runoff volume of the river has been sharply reduced since recent decades, and the dryingup of the river course has occurred frequently, which have seriously threatened the economic development and ecosystems. In this paper, the variation of annual and seasonal runoff volumes and the affecting factors were analyzed based on the data of monthly runoff volumes at 3 hydrological stations of Nancun, Chanzhi Reservoir and Yinfu Reservoir as well as the annual precipitation and air temperature data observed by Qingdao Meteorological Station during the period of 1964-2008. The results showed that the annual runoff volume of the river was in a slight reduction in recent 45 years, but its decadal difference was remarkable, especially since the 1980s. The annual runoff volume at Nancun Hydrological Station became zero for many years. There was a sharp change of annual runoff volumes at the 3 hydrological stations in the early1960s, and also a 4year fluctuation quasiperiodicity of annual runoff volume at Yinfu Reservoir Hydrological Station. Seasonally, 89.8% annual runoff volume at Nancun Hydrological Station occurred in flood season. Moreover, the runoff volume at Nancun Hydrological Station was in a notable reduction in flood season and other months except in August and September, its change was not obvious in nonflood season, but the runoff volume was 0 in most years from the 1980s. Seasonal difference of runoff volume between the hydrological stations of Chanzhi Reservoir and Yinfu Reservoir was low compared with that at Nancun Hydrological Station. Compared with the annual runoff volume during the period of 1964-1980, the percentages of reduced annual runoff depth by precipitation reduction and by human activities during the period of 1981-2008 were 52.38% and 47.62% respectively, which revealed that the runoff variation was strongly affected by these two factors. Furthermore, under the background of global climate change, human activities exacerbated the reduction of runoff volume and resulted in the Dagu River to be as a seasonal river.

Key words: runoff volume, change trend, sharp change, period change, Dagu River Basin, Jiaodong Peninsula