Exposure to geo-hydrological hazards of the metropolitan area of Genoa, Italy: A multi-temporal analysis of the Bisagno stream

Geo-hydrological risk reduction policies are becoming a critical challenge for environmental sustainability, both at the national and international levels. The reason is twofold: On the one hand, climate change has increase rainfall frequency and intensity, while on the other, reckless urban expansion has increased exposure to such hazards over time. Italy is a country that is very vulnerable to flood and landslide hazard; the city of Genoa, which, in recent decades, has been frequently hit by severe floods, has risen to symbolize Italian geo-hydrological risk. Recent studies on Genoa's geo-hydrological hazard have focused on the analysis of hydro-geomorphological features of the Bisagno stream basin, yet their main focus was on hazard control. Very little research has been done to enhance the understanding of the source of risk in such catchments. This paper presents a study on the increased urban exposure and vulnerability to geo-hydrological hazard along the Bisagno stream catchment area over the last 200 years. Morphometric analyses were coupled with historical documents showing the evolution of the urban layout in this area. The results show that the "Bisagno Master Plan", a territorial planning strategy aimed at reducing geo-hydrological hazard and risk, has not produced the expected benefits. In spite of the plan, critical changes in land use and the hydrographic network, along with uncontrolled anthropization of the Genoa metropolitan area, has continued over the last two decades.