Abstract

Research of this paper was conducted in the Luergou Watershed in Tianshui City of Gansu Province of China. By using GIS technology the author established space database and attribute database for the different land use/forest cover in 1985, 1993, and 2001, in order to analyze the variations of runoff of the watershed under different forest cover, and further probed the impact of the forest on the runoff of the watershed. Analysis result shows that the flood runoff module has an exponential relationship with annual precipitation and forest cover rate, i.e. W=ae^bP-cL. Monthly runoff varies with precipitation distribution in a year. Runoff decreases along with increase of forest cover. The result also shows that the runoff process by rainfall is complex, which is affected by many factors such as antecedent rainfall, rainfall volume, rainfall duration, maximum rainfall intensity, vegetation, topography, and soil, etc. A case study on rainfall and flood process indicates that regulation of flood runoff becomes stronger along with the increase of forest cover of watershed.

Keywords: Loess hilly-gully areas, watershed, forest, runoff