In order to investigate the hydrological behaviors of forest and grassland watersheds, a comparative analysis of water balance elements on two experimental watersheds in the gully region of the Loess Plateau was made. The quantitative results of the model applied and observed data confirm that the depth of annual runoff in the forest watershed is less than that of the adjacent grassland on condition that cover degree of both is the same, the amount of evaportanspiration in forest watershed is higher than that of the grassland, and soil water storage in the three-meter horizon is less than that of grassland. So we consider that forest cover strengthens the processes of water vertical circulation, and weakens that of the hydrological cycle, and reduces soil water content. A practical suggestion about forest development in this region is also given in this paper.

Keywords: hydrological behavior, watershed, the Loess Plateau