Probabilistic delineation of flood-prone areas based on a digital elevation model and the extent of historical flooding: the case of Ouagadougou

The delineation of flood-prone areas is one of the most important steps for flood risk assessment and mitigation. This study uses a probabilistic and DEM-based framework for the delineation of flood-prone areas based on information about the extent of historical flooding in the area of interest. This is particularly useful for the delineation of flood-prone areas in cases where more accurate hydraulic profile calculations are not available. The delineation of flood-prone areas is carried out by using the Topographic Wetness Index (TWI) which allows for the delineation of a portion of a hydrographic basin potentially exposed to flooding by identifying all the areas characterized by a topographic index that exceeds a given threshold. A Bayesian updating framework is used for estimating the TWI threshold for identifying the flood-prone areas based on available information on the spatial extent of historical flooding. An application of the proposed method is demonstrated for the delineation of potentially flood-prone areas in the city of Ouagadougou, based on the observed spatial extent of the 2009 flooding event in the city.