Cost–Benefit Analysis of Hard and Soft Flood Risk Mitigation Measures in Urban Areas

ABSTRACT In this paper, a procedure for evaluating and comparing the efficiency between hard and soft flood risk mitigation measures in a highly urbanized area is presented. The European Directive 2007/60/EC promotes, in fact, the implementation of soft measures, which reduce the vulnerability of elements in exposed areas as a risk mitigation strategy and may be less expensive than classic defense measures and sometimes even more effective, but this aspect deserves further investigation. For these reasons, the effectiveness of these hard and soft measures has been here investigated in terms of average annual reduction in expected damage and subsequently through the application of a cost–benefit analysis. The effectiveness of these measures was calculated on a microscale by considering the lifetime of each measure. On the other hand, the efficiency comparison between the different scenarios was carried out at the meso scale, calculating the overall damage reduction for each scenario as the sum of the small contributions of the microscale analysis. The methodology was applied to the case study of the city of Barcellona located within the Longano catchment in the northeastern part of Sicily, Italy. Results showed how the use of soft measures can offer greater efficiency than the use of classical hard defense measures, both in terms of damage reduction and in terms of less time to return from the initial investment.