Effects of agricultural activities on regional hydrology and model diagnosing: A case study at Upper Sangamon River basin

摘要

More and more catchments all over the world are altered by human activities especially agricultural activities, which lead to significant alterations of regional hydrology. Upper Sangamon River basin (USRB) is 3,150 km2 at the confluence of the Illinois River in central Illinois of USA. The USRB is intensively managed, following conversion to intensive agricultural production during the late 19th Century through formation of drainage districts, excavation of drainage ditches and installation of subsurface drainage tiles. In order to detect the effects of agricultural activities on the regional hydrology in USRB, a physically based semi-distributed hydrological model (THREW model) is applied to Upper sangamon River basin. THREW model, based on the Representative Elementary Watershed approach, has been applied to many catchments in China and USA. After model diagnosing, crop transpiration and tile drainage are supposed to be important factors in the rainfall-runoff process. As the crop transpiration is significant in the evapotranspiration due to the high fraction of vegetation cover in USRB, the modeling of evapotranspiration is improved by introducing LAI. Because of the installation of subsurface drainage tiles in USRB to lower the groundwater table, the tile drainage as a kind of interflow is modeled in the model. Through analytical comparison, crop transpiration and tile drainage are found to play important roles in the hydrological process in USRB.