Geo-hydrological hazard and urban development in the Mediterranean area: an example from Genoa City (Italy).

The Ligurian area has always suffered from significant geo-hydrological events causing casualties and serious damage. The atmospheric circulation in autumn and winter coupled with landform peculiarities are the main causes this hazard becoming a risk to human life, structures, and infrastructures. Genoa city and the surrounding metropolitan area are commonly subject to heavy rainfall that induces violent flash floods and many shallow landslides. The most recent rainfall events occurred on 9-10 October and 15 November 2014, again causing loss of human lives and widespread damage. A troubling trend since the beginning of the new century, is the recurrence of such events with greater frequency than in the past. The city of Genoa serves as a very interesting case-study for geo-hydrological risks. Cloudbursts of few hours seem to have a rainfall intensity basically greater than in the past; that causes increase of hydrometric levels of the watercourses that quickly reach alarming values close to the overflowing. This meteorological factor, added to growing urbanization of the valley floors and slopes located north of Genoa, has inevitably produced a general trend of increasing risk for the city. Urbanization is particularly notable for the narrowing process in all cross-sections of Genoa's watercourses, both in the main ones and in the secondary streams that flow directly into the Gulf of Genoa. The narrowing of the sections resulted from the increasing demand for new spaces owing to both industrial development (which started initially at the coastal areas of Genoa), and the growth of the Genoa population. The number of inhabitants grew from fewer than 200 000 at the beginning of the 19th century tool a peak of over 800 000 in the 1970s modifying the water balance of the basins and increasing the geo-hydrological risk in an unacceptable way. Among the important topics analyzed in this paper are: (i) the meteorological characteristics of these events, (ii) the changes in the rate of daily precipitation, and (iii) the most significant periods of the urban land development determining important changes of the territory above all on the hydrographic network. [ABSTRACT FROM AUTHOR]