Impacts of Human Activities on Land Surface Water and Energy—A Case Study in Weishui River Watershed

A typical watershed in the subtropical monsoon region was selected for a case study. A land surface hydrological model for Weishui River Basin was established by coupling the schemes of crop growth, empirical reservoir irrigation and groundwater lateral flow into with a land surface model. First, the model with a constant land cover dataset was used to quantify the impacts of groundwater lateral flow, crop cultivation, groundwater exploitation and reservoir irrigation on land surface water and energy. The land cover change and its effects on the watershed were then investigated using several remote-sensing images and modeling studies. The results show that:1) The groundwater lateral flow makes the simulation more reasonable with lower depth in downstream areas (lower than four meters) and deeper table in mountainous areas (deeper than several decameters); the crop model yields a larger leaf area index than the fixed one, and thus increases the transpiration in cropland, which consumes more water in the watershed and lessens the latent heat flux; irrigation then offsets the water loss by utilizing the surface water and increases the latent heat flux. In addition, it is found that the effect of groundwater pumping is not significant. 2) The land cover changed a lot from 1990 to 2012 with small changes during the 1990-2000 period and large changes during the 2001-2012 period. From 2001 to 2012, the area of cropland first decreased, then increased, and then decreased again (the trend of woodland is opposite); the changes of vegetation types that belong to the same land use type are significant, which leads to large differences in land surface modeling.