Researchers evaluate strategies to protect Venice from rising sea levels
A new paper compares strategies, including movable barriers, ring dikes, closing the Venetian Lagoon, and relocating the city, that could help Venice adapt to future sea-level rise.
The findings could inform long-term planning for the city, but rapid action is essential, the researchers say.
Venice is a UNESCO World Heritage Site within the Venetian Lagoon and has flooded increasingly often over the past 150 years. The city’s current flood defences include a trio of movable barriers at the lagoon’s edge.
An international team of researchers, led by Piero Lionello at the University of Salento, assessed existing and potential adaptation strategies for Venice against sea-level-rise projections from the IPCC’s Sixth Assessment Report.
They estimate that, if additional measures are implemented, the existing movable barriers may be effective against a sea-level rise of up to 1.25 metres. They note this benchmark is likely to be exceeded under a low-emissions scenario (SSP1-RCP2.6) by 2300 due to climate change and ground subsidence.
Alternative options explored by the authors include protecting the centre of Venice with dikes that would separate it from the rest of the lagoon; closing the lagoon with a “super levee”; or relocating the city, its residents and historic landmarks inland. They estimate that dikes may be necessary beyond 0.5 metres of sea-level rise, which may occur by 2100 under the SSP1-RCP2.6 scenario.
The closed-lagoon strategy could also be viable beyond 0.5 metres of sea-level rise, and the authors estimate that this could protect the city against sea-level rise of up to 10 metres. They propose that relocating the city may be necessary beyond 4.5 metres of sea-level rise, which is projected to occur after 2300.
The authors used the costs of previous engineering projects (adjusted for inflation to 2024 prices) to estimate the potential costs and feasibility of each adaptation strategy. They report that the overall cost of building Venice’s existing flood defence system was €6 billion and estimate that construction of dikes could cost between €500 million and €4.5 billion.
Closing the lagoon with a super levee could initially cost more than €30 billion, and relocating the city could cost up to €100 billion.
Dr Roger Cremades Rodeja at the Sustainability Research Institute provided socio-economic insights into the different adaptation pathways, with emphasis on the port, the tourism industry and resident wellbeing.
He analysed how strategies involving an open lagoon (with frequent MoSE closures) or a closed lagoon (requiring permanent dams or relocation) would disrupt shipping and shift regional economic dynamics.
Here, the cost of inaction, or the wrong action, could run into billions. For tourism, he examined how each pathway would affect the preservation of cultural heritage and the delicate balance between economic revenue from tourism and resident well-being.
He said: “No single strategy is optimal. The choice reflects what society values most and how far ahead it plans. Human ingenuity is unpredictable, yet planning is necessary: cities must recognise that building large-scale defences can take decades.”
The authors note that any approach taken must balance the wellbeing and safety of Venice’s residents with economic prosperity, the future of the lagoon’s ecosystems, heritage preservation, and the region’s traditions and culture. They caution that, as the construction of large-scale interventions such as permanent barriers can take between 30 and 50 years, early planning is essential.
