Exposure to Geo-Hydrological Hazards of the Metropolitan Area of Genoa, Italy: A Multi-Temporal Analysis of the Bisagno Stream

Abstract

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 Morphometric analyses were coupled with historical documents showing the evolution of the urban layout in this area.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.

Flood-induced ground effects and flood-water dynamics for hydro-geomorphic hazard assessment: the 21–22 October 2019 extreme flood along the lower Orba River (Alessandria, NW Italy)

“…River-related floods occur frequently in large areas of the world (Bathrellos et al, 2018), and are the most prevalent natural hazard and among the most damaging events in Europe (EEA, 2010(EEA, , 2016Gaume et al, 2009;Kundzewicz et al, 2013Kundzewicz et al, , 2018Llasat et al, 2010). Long lists of past inundations and relative damage testify the relevant flood-proneness of Italy (Brandolini et al, 2020;Faccini et al, 2015Faccini et al, , 2016Luino et al, 2002;Mandarino et al, 2019aMandarino et al, , 2020aPavese et al, 1992;Roccati et al, 2020;Salvati et al, 2012;Zani, 2000), where there were 581 deaths and 171,764 evacuated and homeless due to floods in the 50-years period 1969-2018(CNR-Polaris, 2019, and about thirty floods and a hundred victims from 2010 to 2019 (Paliaga et al, 2020).…”

Geo-Hydrological Events and Temporal Trends in CAPE and TCWV over the Main Cities Facing the Mediterranean Sea in the Period 1979–2018

“…Notwithstanding this, land use and vulnerability conditions have probably played an important role in this differentiation between the North African countries and the European ones. Large European territories suffer for a high percentage of soil sealing and for the lack of proper risk mitigation measures [67][68][69][70][71], which influence the impact of severe events. Nevertheless, the different economic conditions of north African territories cause a further planning inadequacy [72,73] for land usage, exposing them to a high geo-hydrologic risk.…”

Coupling Historical Maps and LiDAR Data to Identify Man-Made Landforms in Urban Areas

“…In the early 19th century, the two main valleys, the Polcevera to the West and the Bisagno to the East, were characterized by an agricultural landscape with a dense pattern of small fields across the floodplain and terraces over the slopes with a prevalence of vineyards and olive orchards [45,46]. Terraces are only partly visible in the current landscape and have been largely obliterated by more recent urban structures, decametric retaining walls, and high blocks of flats of the second half of the 20th century [47]. Urban expansion brought hydraulic works in the two valleys, with progressive narrowing of the riverbeds and the establishment of new urban areas in the floodplains in the early 20th century up to the 1930s [12].…”