Venice, built on 120 small islands with 177 canals and nearly 400 bridges, faces an existential threat from rising seas and sinking foundations. Multiple reports indicate that global sea levels could rise by up to seven meters over the next 300 years, and a 16-meter rise cannot be ruled out. The city has experienced 18 extreme flooding events in the last 23 years.
Current defenses, including three movable barriers at the lagoon's edge, may only be adequate up to roughly 1.25 meters of sea level rise, even with additional pumps, researchers said. A team from the University of Salento assessed four potential strategies: more movable barriers, ring dikes, a super levee, and relocation. The authors said dikes or closing the lagoon may be necessary for a 0.5-meter sea rise, possibly before 2100.
Under extreme sea level rise, relocation of monuments to suitable inland areas and abandonment would be the only remaining strategy, which might become unavoidable in the 22nd century under current climate policies and an Antarctic ice-sheet collapse.
Relocating the most historically significant parts of Venice may be more feasible than constructing additional flood defenses, according to researchers. The study, which referenced the relocation of the Abu Simbel temples in Egypt between 1964 and 1968, estimated relocation would cost $100 billion (£87 billion). The authors said relocation might be necessary beyond 4.5 meters of sea level rise, projected after 2300. "Under extreme sea level rise, relocation of monuments to suitable inland areas and abandonment would be the only remaining strategy, which might become unavoidable in the 22nd century under current climate policies and an Antarctic ice-sheet collapse," the University of Salento team said in a press release.
Planned relocation and abandonment by residents are two components of the retreat strategy.
Planned relocation consists of dismantling buildings and reassembling them in new higher locations. This unprecedented and complex operation would not prevent the loss of the cultural, historical and monumental assets of the original settlement.
The relocated monuments could be visited by tourists and new residential areas built around them. The flooded remains would progressively deteriorate and could be visited for a limited period by boat.