Implementing the Floods Directive: uncertainties in damage modelling

Risk assessments, as emphasized by the Floods Risk Directive, are becoming the basis for a rational decision-making in planning and designing flood risk reduction measures throughout Europe. In this context, the estimation of flood damages in quantitative terms is a key issue for implementing the Directive, as risk is expressed as a combination of the likelihood of flood occurrence and the impact associated with the event. However damage estimates are still affected by high uncertainty, mainly related to the use of depth-damage functions and methodological differences between the existing models; in addition, for some countries, like Italy, where there are no specific curves, a transfer of damage models from other areas is required, adding extra uncertainty in the modelling process. The present paper investigates the reliability of estimates of potential direct flood damage, comparing the influence of hazard and damage components in risk assessments; this is obtained by varying one factor at a time and using different damage models available in literature, in two case studies of cost-benefit analysis for flood detention basin systems. The results show that the total uncertainty is mainly related to the use of the depth-damage curves, whilst hazard modelling has minor influence.