Understanding the effects of digital elevation model resolution and building treatment for urban flood modelling

A mountain city in the coastal region of Southeast China. This study elucidated the effect of digital elevation model (DEM) resolution on flood simulation errors and inundation depth distributions through building treatment methods and river channel definition. The optimal DEM resolution was evaluated to determine whether satisfactory inundation simulation could be achieved for urban flash flood simulation (UFFS) and fluvial overbank flood simulation (FOFS). New hydrological insights for the region: UFFS and FOFS presented opposite effects regarding inundation extent and the spatial distribution of inundation depth with coarsening DEM resolution. In UFFS, the inundation extent and inundation depth in low-lying areas of the flood propagation pathway were underestimated. This effect was attributed to the change of local flood pathway caused by different treatment of buildings at coarser DEM resolution. The simulation error was magnified considerably when the DEM resolution was greater than the building width and gaps. In FOFS, owing to the changed channel geometry at coarser resolution, the inundation extent and inundation depth were overestimated. Using a DEM resolution and computational cell size that are lower than the river width is recommended. This study illustrated that a regional-scale effect, dependent on regional flood propagation behaviour and the impact of land use and topography on the flood propagation pathway, could be observed by coarsening the DEM resolution of inundation simulations. •Contrasting flood propagation behaviours cause opposite effects with coarser DEMs.•A DEM coarser than building width and gap significantly magnifies errors for UFFS.•A DEM resolution lower than the river width is recommended for FOFS.•A regional-scale effect at coarser DEM depends on land use and flood behaviours.