An eight-neighborhood connected collocated grid scheme for overland flow simulation

This study proposes a novel two-dimensional numerical scheme applicable to a wide range of overland flow phenomena, including runoff, flood inundation, storm surge, and tsunami wave runup. In conventional structured grid models, water movement is restricted to four directions, which can lead to artificial depressions, flow blockages, and spurious storage owing to grid orientation effects. To overcome this limitation, we developed an eight-neighborhood connected collocated grid that integrates the advantages of collocated and staggered grids, enabling flux exchanges in all eight directions, and applied it to shallow water equations. Numerical experiments, including wave propagation simulations and benchmark rainfall–runoff tests in an idealized catchment, were conducted and compared with a conventional staggered grid method. The proposed method successfully reproduced wave propagation with comparable accuracy and demonstrated a robust runoff simulation performance that was independent of grid orientation and resolution.