HydroSCAPE: A multi-scale framework for streamflow routing in large-scale hydrological models

We present HydroSCAPE, a large scale hydrological model with an innovative streamflow routing scheme based on the Width Function Instantaneous Unit Hydrograph (WFIUH) theory, which is designed to facilitate coupling with weather forecasting and climate models. HydroSCAPE preserves geomorphological dispersion of the river network when dealing with horizontal hydrological fluxes, irrespective of the adopted grid size, which is typically inherited from the overlaying weather forecast or climate model. This is achieved through a separate treatment of hillslope processes and routing within the river network, with the latter simulated by suitable transfer functions constructed by applying the WFIUH theory to the desired level of detail. Transfer functions are constructed for each grid cell and nodes of the network where water discharge is desired by taking advantage of the detailed morphological information contained in the Digital Elevation Model of the zone of interest. These characteristics render HydroSCAPE well suited for multi-scale applications, ranging from catchment up to continental scale, and to investigate extreme events (e.g. floods) that require an accurate description of routing through the river network. The model enjoys reliability and robustness, united to parsimony in the adopted parametrization and computational efficiency, leading to a dramatic reduction of the computational effort with respect to full-gridded models at comparable level of accuracy of routing. Additionally, HydroSCAPE is designed with a simple and flexible modular structure, which makes it particularly suitable to massive parallelization, customization according to the specific user needs and preferences (e.g. choice of rainfall-runoff model), and continuous development and improvements.