Uncertainty in risk maps. Application to floods and marine submersion hazards

Maps of hazard delineation are an essential tool for managing natural risks, in order to prevent and prepare exposed populations. But natural hazards remain phenomena subject to many uncertainties, both in their definition and their delimitation. The aim of this research is to analyse the sources of uncertainty in the delimitation and the representation of marine submersion and flood hazards, based on a sample of hazard maps extracted from Risk Prevention Plans (PPR) in France. This analysis shows that the main causes of uncertainty are attributable to the semantic ambiguity of hazard classes, the lack of specification of hazard modelling methods and their parametrization, and the imperfection of the data used. However, the only uncertainty clearly presented in these maps remains the use of several hazard classes corresponding to varying levels of intensity. In addition, analysis of the cartographic representation choices reveals the heterogeneity of practices in the construction of hazard maps, both in terms of the number of classes and symbology used, which can lead to confusion. Uncertainty of hazard delineation combined with confusion of cartographic representations can generate forms of cartographic uncertainties. To reduce these cartographic uncertainties in hazard maps, recommendations based on harmonized cartographic practices are proposed.