Is anthropogenic land subsidence a possible driver of riverine flood-hazard dynamics? A case study in Ravenna, Italy

We investigate possible changes in flood hazard over a 77-km2 area around the city of Ravenna. The subsidence rate in the area, naturally a few mm year−1, increased dramatically after World War II because of groundwater and natural gas extraction, exceeding 110 mm year−1 and resulting in cumulative drops larger than 1.5 m. The Montone–Ronco river system flows in the southern portion of the area, which is protected against frequent flooding by levees. We performed two-dimensional simulations of inundation events associated with levee breaching by considering four different terrain configurations: current topography and a reconstruction of ground elevations before anthropogenic land subsidence, both neglecting and representing the main linear infrastructures (e.g. roads, artificial channels). Results show that flood-hazard changes due to anthropogenic land subsidence (e.g. significant changes in computed water depth and velocity) are observed over less than 10% of the study area and are definitely less important than those resulting from construction of the linear infrastructures.