Evoluzione temporale del sedime edilizio nella Versilia pre-alluvione 1996 in rapporto alle mappe di pericolosità idraulica e da frana mediante software GIS open source e open data

Settlement temporal evolution in Versilia up to the 1996 flood in relation to the hydraulic and landslide hazard maps using software open source and open data. The 19 June 1996 flood affected a heavily urbanized area: the study of the settlement distribution in areas characterized by a hydraulic or landslide hazard is mandatory in the prevention activity. In this work the diachronic evolution of the urbanization in some basins of the Versilia area (Tuscany) from 1950 to 1996 was analyzed. The study considers the temporal evolution of the urbanization in order to depict the settlement structure just before the 1996 flood, taking into account the hydraulic and landslide hazard maps produced by the local river basin authorities. In particular, the goal of this work is the identification of the periods characterized by a low or increased awareness in the importance of the hydraulic and landslide hazard cartography. The available data highlight a remarkable difference in the number of buildings constructed in areas characterized by a hydraulic and landslide hazard from 1850 to 1996. In fact, before the June 1996 flood, only the 6% of buildings were constructed in areas characterized by landslide hazard, while the 71% of buildings were constructed in areas characterized by hydraulic hazard. In particular, in the investigated period the number of buildings constructed in areas with landslide hazard seems to flatten out, while the number of buildings constructed in area with hydraulic hazard shows a significant increase between 1954 and 1978. After this period (until 1996) there is a decrease in the number of buildings constructed in areas affected by environmental hazards. However, this trend might not be due to an actual increase in the awareness to hydrological and landslide hazard, as suggested by the growth of the number of buildings constructed in areas characterized by the highest hazard level.