Significant additional measures needed to protect Venice from rising sea levels
Expert(s) |
Valeria Di Fant
|
Marjolijn Haasnoot
Flooding in Venice is becoming increasingly frequent and poses a growing threat to the city and the lagoon. The cause is relative sea-level rise: a combination of sea-level rise due to climate change and local land subsidence, which has been making Venice more vulnerable for over 150 years. New research by the University of Salento, the University of East Anglia, University of Venice, and Deltares, among others, shows that, in addition to existing protection, further adaptation measures are inevitable to keep Venice liveable in the long term.
MoSE offers protection, but has its limits
Since 2020, Venice has been protected by the MoSE system: three movable storm surge barriers at the entrances to the lagoon. In the event of extremely high water levels, these barriers temporarily seal off the city from the Adriatic Sea. This prevents large-scale flooding, such as that of 1966, which prompted decades of planning and ultimately the construction of MoSE.
The system is currently functioning well, but rising sea levels are putting MoSE under increasing pressure. With a sea-level rise of approximately 0.5 metres, the barriers would already need to be closed for up to two months a year. This has major consequences for the water quality of the lagoon, the ecosystem, shipping, the port and tourism. The risk of malfunctions also increases, and additional drainage and pumping systems are required to control the water level in the lagoon.
Researchers estimate that MoSE, provided it is supplemented with additional measures, can remain effective up to a sea-level rise of approximately 1.25 metres. Beyond that, more radical and transformative choices will be necessary.
Sea-level rise is hitting Venice hard
Venice is particularly vulnerable. More than half of the city currently lies between 0.8 and 1.2 metres above mean sea level, whilst the tidal range reaches around one metre. Projections based on the Sixth IPCC Report show that global sea levels could rise by around 0.4 metres by 2100 under strong climate mitigation (SSP1-RCP2.6) and by 0.8 metres or more under high emissions (SSP5-RCP8.5).
Even greater rises in the longer term cannot be ruled out. Without protection, under such scenarios, a large part of the historic city centre would be flooded daily during high tides.
Four routes for the future
In a recent study published in the journal Nature Scientific Reports, researchers analysed various long-term adaptation strategies for Venice:
Open lagoon with supplementary measures
Continuation of the current MoSE system, combined with local adaptations such as raised buildings, mobile flood barriers and adapted public spaces. This strategy offers flexibility, but primarily buys time.
Protection of the city with dykes
The construction of a dyke ring around the historic centre, separate from the rest of the lagoon, combined with pumping and adapted water management. This option may become necessary if sea levels rise by more than 0.5 metres.
Closing off the lagoon
A ‘super-dyke’ that completely seals off the lagoon from the sea. This strategy could protect Venice even with a sea-level rise of several metres, but would have major consequences for nature, the landscape, culture and the economy.
Managed retreat
In the event of a very significant sea-level rise, expected to exceed approximately 4.5 to 5 metres after 2300, the relocation of residents and heritage (‘managed retreat’) may become unavoidable. Venice would then undergo a fundamental change in function and significance.
Costs, timing and societal choices
The construction of MOSE cost approximately 6 billion euros. New measures are also costly: dykes around the city are estimated at 0.5 to 4.5 billion euros, closing off the lagoon at over 30 billion euros and relocating (parts of) the city at up to 100 billion euros.
These figures do not yet take cultural and historical values into account. Furthermore, large-scale interventions require 30 to 50 years of preparation and implementation. Starting on time is therefore essential.
Long-term adaptation pathways and ‘tipping points’ for Venice. Adaptation can begin with the open-lagoon strategy, but other strategies will be needed in the long term.
Beyond Venice
According to author Valeria Di Fant (researcher at Deltares, Utrecht University), Venice demonstrates that much is technically possible, provided society and politicians are willing to invest: “Extra large-scale adaptation measures are needed for Venice to survive. Every choice requires a careful balance between safety, the economy, ecosystems, heritage and culture.”
Author Marjolijn Haasnoot (researcher at Deltares and Utrecht University) emphasises that the lessons extend beyond Italy: “Venice is unique, but the challenge is universal. All low-lying coastal areas would do well to start thinking now about long-term sea-level rise. Early decisions broaden the scope for action and make investments more sustainable.”
In summary
Venice cannot rely on a single solution. Additional measures are necessary, cost money and require timely decision-making. By investing now in supplementary protection and adaptation, the lifespan of MoSE can be extended.
In the longer term, fundamental choices are needed: protecting the city with dykes, closing off the lagoon, or, in the event of extreme rises, controlled abandonment of parts of Venice.
