Runoff simulation using a modified SWAT model with spatially continuous HRUs

The Soil and Water Assessment Tool (SWAT) model is a well-established eco-hydrologic model that employs the hydrological response unit (HRU) as the basic unit. Land surface patches within one HRU have identical hydrological properties (e.g., land use, soil, slope and management) and thus have similar hydrological responses. The non-spatial aspects of HRUs, however, are considered a key weakness of the SWAT model because it is difficult to determine the spatial locations and describe the interactions between different HRUs. Here, a new method to produce continuous HRUs with a clear spatial position for SWAT using Geographic Information System tools is proposed and then tested in a small catchment of the Taihu Basin, China. The SWAT model was then modified based on spatial continuous discretized HRUs accounting for the surface runoff lag difference of HRUs in one sub-basin. The results showed that the modified model was more sensitive to the lag in runoff processes and thus had better simulation accuracy.