**6. Conclusions**

Two factors, which are very different from each other, are at the basis of the geohydrological processes that have affected long stretches of the Mediterranean coast in recent decades. The first, which is of anthropogenic origin, is the urban expansion that began after the end of the Second World War. The second, which is of "apparently" natural origin, is climate change (for which the role played by man is now very clear to everyone). The combination of these two factors, which are in some manner very distant from each other, is now causing a situation that is difficult to manage and that places us at the forefront of real emergencies for which it will be necessary to utilize precise analytical tools, sensible land use planning and rapid and resolving interventions.

The floods that occurred in Genoa, Olbia and Livorno revealed the state of vulnerability of the city towards hydraulic processes in spite of many accurate mitigation interventions carried out in the last decades and above all the inadequacy of the current urban fabric in relation to the hydrographic network, both on the hydraulic and geomorphological level.

The comparison between the events described highlights the need to plan flood risk mitigation activities beyond the essential structural interventions on the hydrographic network, whether it be main and minor and at basin scale (extraordinary maintenance), which involves inevitable financial programs that are costly and delayed over time. It appears essential that we prepare non-structural measures which includes both active (routine maintenance, thickening of the weather-hydrological monitoring and construction of expansion tanks) and passive (land use rules with intensive use of urban drainage systems sustainability, foreclosure of fluvial pertinence areas, historical investigation of past events, population trainings, information to inhabitants and insurance coverage) measures.

With regard to the actions to be taken in the short-term and medium-term in order to adapt to the resurgence of flash flood effects on the ground, there are several methodological examples for the Mediterranean area that involve urban, social and economic choices. For example, we want to mention the TRIGEAU project [77] and the ADAPT project [78], which suggests strategies to mitigate the effects of climate change. In particular, the ADAPT project suggests: (1) Actions to improve geo-hydrological conditions, such as increasing knowledge on the processes that contribute to the occurrence of geo-hydrological criticalities, adapting existing mitigation works, carrying out interventions for urban flood mitigation and urban greening interventions; (2) actions to increase the resilience of the population and assets at risk with training activities; (3) actions to improve governance with legislative adjustments, urban interventions and limitations on urbanization and restoration of areas of river pertinence and re-naturalization.

Until the state and every single municipality decides to take serious and decisive action to solve this age-old problem, the flash floods will continue to cause victims and massive damage to private and public property.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/2073-445 X/10/6/620/s1, Table S1: Land use in the studied catchments, Table S2: Dates of post-World War II flood events in the three studied cities.

**Author Contributions:** Conceptualization, F.L., F.F. and L.T.; methodology, F.L., F.F. and L.T.; software A.R. and G.P.; validation, A.R., G.P., F.L., F.F. and L.T.; investigation, G.P., F.L., F.F. and L.T.; resources, A.R., G.P., F.L., F.F. and L.T.; data curation, A.R., G.P., F.L., F.F. and L.T.; writing—original draft preparation, F.L., F.F. and L.T.; writing—review and editing, F.L., F.F. and L.T.; visualization, A.R., G.P., F.L. and L.T.; supervision, G.P. and L.T.; project administration, F.L. and L.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
