Effects of Vegetation Cover on Hydrological Processes in a Large Region: Huaihe River Basin, China

Abstract

Vegetation plays an important role in water and energy cycles on land surfaces. Nevertheless, the physical effects of vegetation are not explicitly considered in many hydrologic-modeling works. In this study, a coupled land-surface-hydrologic model was used to investigate the vegetation effects on hydrologic processes over the years 1980–1987 in the Huaihe River basin, China. The vegetation coverage of the basin was assessed by the International Satellite Land Surface Climatology Project (ISLSCP) Initiative II historic and potential land cover data set. Farmland was declared the dominant vegetation type of the basin in 1970 by the historic land cover scenario, and the potential vegetation cover is mixed forest. Firstly, the coupled model was calibrated by observed streamflow at Bengbu station. The correlation coefficient and Nash-Sutcliffe coefficient of efficiency of multiannual daily series were 0.987 and 0.968, respectively, which indicate that the capability of the coupled model system is acceptable. Next, typical hydrologic physical processes, including evapotranspiration (ET), soil moisture, surface runoff, and groundwater, were simulated and analyzed for the two vegetation scenarios with same meteorological data, initial conditions, and model parameters. Results indicate that mixed forest has larger ET than farmland for most rainfall events. Compared to the farmland scenario, mixed forest has higher soil moisture in top layer; but mixed forest has a lower soil moisture in deep layer because of more transpiration. Surface runoff with mixed forest decreases significantly compared with the simulated values with farmland, and groundwater is reduced also because there is less drainage and more transpiration in mixed forest. Accordingly, streamflow at Bengbu station decreases by approximately 11% with the potential mixed forest. This study indicates that forestation is effective at reducing peaks of floods.