Increased flash flooding in Genoa Metropolitan Area: a combination of climate changes and soil consumption?

The Genoa Metropolitan Area (GMA) has been historically affected by floods for two reasons, namely meteorological conditions and the city’s geographical arrangement. In the past few years in GMA, an increase in flash floods has been registered; among the causes, climate variations have been analysed. In 2014, several floods took place. In some areas of the hinterland, the cumulative annual rainfall exceeded 4000 mm. This research analyses the rainfall statistics collected by Genoa University and Chiavari stations (GMA along the coast) and at Isoverde and Diga Giacopiane stations (hinterland of GMA). The analysis was based on the mean annual, seasonal and monthly rainfall and rainy days for the four stations and daily series for Genoa University. Furthermore, annual maximum data of hourly rainfall for the Pontecarrega station were analysed. The annual rainfall does not show any trend. The monthly analysis highlights significant decreases for rainfall and rainy days between spring and summer. Climate indices recorded on daily data at Genoa University station show a certain increase in rainfall intensity in recent years. Additionally, hourly rainfall at 1 and 3 h increased, and the series showed a change point in the 1990s. Furthermore, urban sprawl has continually increased until now, and its contribution has already been accepted. These facts can be related to the intensification of flash flood events measured in the last decade. Furthermore, historical data from several sources confirm an increase in the number of events and casualties. These conditions determine a clear need for monitoring potentially hazard situations.