Appraising and reducing riverine flood risk: a case study from Central Italy

On 15 September 2022 a catastrophic flood event hit the Misa river basin in Central Italy. The magnitude of the event (intensity of precipitation, water discharge, debris and sediment transport) and the subsequent impacts were far more severe and extended than previous flood events in the same area, thus calling for a radical change in current practices of flood risk management. In this framework, the present study aims at 1) providing a comprehensive assessment of flood risk for the Misa river basin, and 2) designing appropriate risk reduction measures at river basin scale. We reconstructed the September 2022 event by integrating in-field surveys, hydrological data, hydraulic models, observations of the event (e.g. flood extent maps) and historical data of past flood events, taking into account the incompleteness and uncertainty of both models and observations. Moreover, we modelled exposure and vulnerability of population and economic activities in the area, using detailed surveys of observed impacts to inform the model set-up. The outcomes of these activities allowed to review the risk analysis tools currently available in the Misa river basin, and to design updated risk scenarios for present and future climate conditions. Finally, the risk scenarios have been used to explore different alternatives for flood risk reduction, in agreement with local authorities and stakeholders. We evaluated a range of structural measures (strengthening of dike systems, detention areas, river diversions) and non-structural measures (land-use planning, relocation, flood-proofing measures), considering existing risk management plans and new analyses carried out in this study (e.g. cost effectiveness of measures).