Spatial-temporal analysis of the subsidence in the city of Bologna

The land subsidence induced by groundwater withdrawal is particularly troublesome, primarily because settlements develop with relatively fast rates but, moreover, because it often affects densely populated areas where exposure to risk is particularly high. In the second half of the last century, several cities of northern Italy suffered subsidence determined by an intensive exploitation of groundwater. One of the cases worthy of major attention is the city of Bologna, which holds a significant heritage of historical buildings and monuments and where settlement as high as 4 m have been recorded. This paper reports a study on the spatial distribution of the phenomenon and its evolution with time. The data recorded by a number of sequential topographical campaigns and, more recently, with satellite surveys, cover a period of more than 60 years (from 1943 to 2005) and an area of 272.25 km2. The spatial analyses, performed with the support of a Geographical Information System, have revealed a progressive development of settlements with different time histories over the territory. The distribution of total and differential settlements is consistent with the characteristics of the subsoil, the groundwater withdrawal activity and the effects noticed on buildings.