Sea level rise, hydrologic runoff, and the flooding of Venice

This paper deals with hydrologic studies relevant to the works engineered for the protection of the city of Venice (Italy) from major flooding under significant climate change scenarios. Such works foresee the temporary closure of the lagoon surrounding the city to tidal exchanges with the Adriatic Sea in times of sea storm surges via the operation of a set of mobile gates. A general hydrologic model of the approximately 2000 km2 mainland contributing runoff to the lagoon of Venice is coupled in time and space with a 2-D finite element model of the relevant tidal hydrodynamics to forecast maximum lagoonal surges in times of closure. We also study the impacts of run-through discharges bypassing the mobile gates and wind setups at time scales comparable to the foreseen closures (from a few to tens of hours). Climate change scenarios are recapitulated by up to +50 cm relative sea level rises by 2100 (the projected lifetime of the current protection works). Possible flooding of the city due to residual fluxes entering the lagoon during prolonged closures is examined. A probabilistic framework is also proposed for computing the statistics of maximum lagoon rises and stage-rise durations. Our studies suggest the adequacy of the design of temporary closures with respect to flooding and provide methods for general exercises in assessing the impact of regional climate change scenarios.