Landslide susceptibility mapping is essential for a suitable land use managing and risk assessment. In this work a GIS-based approach has been proposed to map landslide susceptibility in the Portofino promontory, a Mediterranean area that is periodically hit by intense rain events that induce often shallow landslides. Based on over 110 years landslides inventory and experts’ judgements, a semi-quantitative analytical hierarchy process (AHP) method has been applied to assess the role of nine landslide conditioning factors, which include both natural and anthropogenic elements. A separated subset of landslide data has been used to validate the map. Our findings reveal that areas where possible future landslides may occur are larger than those identified in the actual official map adopted in land use and risk management. The way the new map has been compiled seems more oriented towards the possible future landslide scenario, rather than weighting with higher importance the existing landslides as in the current model. The paper provides a useful decision support tool to implement risk mitigation strategies and to better apply land use planning. Allowing to modify factors in order to local features, the proposed methodology may be adopted in different conditions or geographical context featured by rainfall induced landslide risk.

The metropolitan area and the city of Genoa has become a national and international case study for geohydrological risk, mainly due to the frequency of floods. In 2014, there were landslides again, as well as flash floods that have particularly caused casualties and economic damage. The weather features of the Gulf of Genoa and the geomorphological–environmental setting of the Ligurian coastal land are the predisposing factors that determine heavy rains and their resulting effects on the ground. This study analysed the characteristics of the main meteorological disasters that have hit Genoa since the start of the 20th century; changes in the rainfall regime are evaluated and the main stages of urbanization of the area are detailed, with the resulting changes to the drainage network, in order to identify the main causes of this high geohydrological risk. To this end, scientists have used climate data recorded at the station of Genoa University, in operation since 1833, and at Ponte Carrega station, located in the middle reach of the Bisagno stream, a well-known watercourse because of its frequent floods. Urban sprawl was evaluated through a multi-temporal mapping comparison, using maps available from the beginning of the 19th century up to the current regional technical maps. The average air temperature in Genoa shows a statistically significant increase, while the number of rainy days displays an equally clear decrease over time. The total annual rain value does not seem to indicate rather noticeable changes. The intensity of rain in Genoa expressed as rainfall rate, i.e.~the ratio of annual rainfall and number of rainy days, shows statistically significant growth. The geohydrological vulnerability in Genoa has increased over time due to urban development which has established modifications in land use, from agricultural to urban, especially in the valley floor. Waterways have been confined and reduced to artificial channels, often covered in their final stretch; in some cases they have even been totally removed. These actions should be at least partially reversed in order to reduce the presently high hydrological risk.