Variable Runoff Generation Layer distributed hydrological model of hilly regions

The variable runoff generation layer concept is proposed based on the new understanding of hillslope hydrological experiments to address the problem of flash flood forecasting in hilly regions. This concept has expanded the depiction of interflow from soil horizon to soil-weathering bedrock interface and provided a unified description of the infiltration excess and the saturation excess runoff and their conversion mechanism by meticulously depicting the formation and development process of interflow. Based on the concept of variable generation layer and the theory of kinematic wave model, the calculation formulas of infiltration excess (Horton), saturation excess (Dunne) surface runoff, and interflow of the unit grid are derived. The nonlinear reservoir method, 2-d diffusion wave equation, and 1-d diffusion wave equation are applied to calculate the groundwater flow, the surface runoff routing, and channel flow routing separately, based on which established the variable runoff generation layer distributed hydrological model (VRGL). The VRGL model is applied to the Tunxi watershed, a typical humid watershed of the hilly region. 24 flood events ranging from 2010 to 2019 were studied, and the results showed that the relative error of the flood peak and the flood volume were both within ±20%, and the Nash-Sutcliffe efficiency (NSE) was around 0.84. It is indicated that the accuracy of the VRGL model is high enough for flash flood forecasting in hilly regions.