Floodwater pathways in urban areas: A method to compute porosity fields for anisotropic subgrid models in differential form

•Flood modelling in real urban areas is a challenge for differential anisotropic porosity models.•Direction-dependent, cell-based conveyance porosity is not trivial to estimate.•A method is proposed to extract conveyance porosity fields from building footprints.•Straightforward application to comple...

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