Probabilistic Flood Hazard Mapping Using Bivariate Analysis Based on Copulas

This study presents a methodology to extract probabilistic flood hazard maps in an area subject to flood risk, taking into account uncertainties in the definition of design hydrographs. Particularly, the authors present a new method to produce probabilistic inundation and flood hazard maps in which the hydrological input (i.e., synthetic flood design event) to a 2D hydraulic model has been obtained by using a bivariate statistical analysis (copulas) to generate flood peak discharges and volumes. This study also aims to quantify the contribution of boundary conditions’ uncertainty in order to evaluate the effect of this uncertainty source on probabilistic flood hazard mapping. Different combinations of peak discharge and relative flood volume, obtained by the copula, mean the uncertainty of extreme flood events. Further, the authors analyzed the role of a multivariate probability hydrological analysis on inundation and flood hazard maps, highlighting the differences between deterministic and probabilistic approaches. The methodology has been tested in a study area, located in Sicily, which was subjected to several flooding events in the past.