Numerical modelling of land subsidence related to groundwater withdrawal in the Firenze-Prato-Pistoia basin (central Italy)

The Tuscany region of Italy is widely affected by subsidence, landslides and floods, which severely impact buildings and infrastructure. In particular, Firenze-Prato-Pistoia basin has a long experience of ground deformation related to groundwater withdrawal. European remote-sensing satellite (ERS) data collected since 1992 have revealed the presence of several subsiding areas in the basin such as the south-eastern portion of the city of Pistoia. Sentinel-1 persistent scatterer interferometry (PSI) measurements for 2015–2018 confirmed the long-term subsidence of this area, associated with intense horticulture (plant nurseries). At the same time, Sentinel-1 data revealed the unexpected movement of Pistoia historic center, which has always been considered stable in the past. To identify the complex relationship between aquifer conditions and ground displacement, a hydrogeologic model of the Pistoia aquifers was developed, applying an integrated modelling procedure. Hydrodynamic-parameter distributions, calibrated and validated by means of Sentinel-1 PSI measurements, suggest that subsidence in Pistoia area is probably related with the combined impacts of groundwater extraction and highly compressible aquitards. To evaluate the potential evolution of ground displacement, numerical simulations were extended until 2050, using regional and global climate model data, analyzing three different pumping-rate scenarios. This led to the development of several subsidence hazard maps of the city of Pistoia that display the influence of groundwater extraction in controlling land subsidence in the area. This study emphasizes the importance of developing proper groundwater management policies, especially in alluvial aquifers made of fine compressible sediments, in order to sustainably utilize underground freshwater resources and to avoid related side effects.