The escalating sea levels pose a dire threat to Venice, with indications suggesting the potential submersion of this esteemed UNESCO World Heritage site within the subsequent three centuries.
A consortium of European and UK scientists has meticulously evaluated four proposed strategies aimed at safeguarding the renowned ‘floating city’ from permanent inundation.
These strategies, spearheaded by oceanographer Piero Lionello from the University of Salento in Italy, encompass the deployment of mobile storm surge barriers, the construction of encircling dikes, the complete sealing of the Venetian Lagoon, and ultimately, the relocation of the city itself. Each option was assessed for its efficacy under projected sea level rise scenarios, contingent upon various future greenhouse gas emission trajectories.
The phenomenon of sea level rise is intrinsically linked to anthropogenic fossil fuel combustion, which augments atmospheric greenhouse gases that, in turn, trap solar radiation, a process leading to global warming.
This accumulated thermal energy, commonly referred to as global warming, is progressively absorbed by the Earth’s oceans, landmasses, ice formations, and atmosphere.
The confluence of glacial meltwater and the thermal expansion of oceanic bodies, coupled with an increasing frequency and intensity of storm events, is resulting in the encroachment of marine waters onto landmasses previously untouched for millennia.
Despite the affectionate moniker ‘floating city,’ Venice is not literally buoyant. For over 1,600 years, its foundations have been secured by millions of wooden pilings, a testament to remarkable historical engineering.
Compounding the issue of sea level rise driven by climate change, the very ground upon which Venice is built is experiencing subsidence.
In the last century and a half, the city, its constituent islands, and the surrounding lagoon have borne witness to a marked increase in flood occurrences. Of the 28 major inundation events impacting Venice, wherein upwards of 60 percent of the urban area was submerged, a staggering 18 have transpired within the past two and a half decades.
Current defenses against storm surges originating from the Adriatic Sea are limited to the slender barrier islands delineating the lagoon’s perimeter and a trio of mobile barriers, commissioned in 2022, capable of sealing the lagoon’s access points.
The research conducted by Lionello and his colleagues indicates that these existing measures fall short of providing adequate protection for the canal-laced metropolis against its eventual submersion.
The Open Lagoon Approach
The initial strategy examined, the perpetuation of the ‘open lagoon’ methodology, entails the deployment of retractable barriers at the lagoon’s entrances during periods of elevated flood risk. The existing infrastructure for this strategy has already incurred an expenditure of approximately €6 billion (roughly US$7 billion).
While this approach offers an improvement over inaction, climate modeling derived from the IPCC’s Sixth Assessment Report suggests that its efficacy diminishes significantly with a sea level rise of 1.25 meters (4.1 feet) – a threshold anticipated to be crossed by 2300, even under optimistic low-emission scenarios.
“As the frequency of lagoon closures escalates, so too does the likelihood of operational failures or delays, thereby compromising the level of protection afforded to historical landmarks and the general safety of the populace,” stated Lionello and his co-authors in their published findings.
In scenarios involving prolonged multi-day closures, the implementation of sophisticated sewage treatment and extensive pumping systems would become imperative to maintain water quality.
Encircling Dikes
This proposed solution involves the construction of approximately 3-meter-high circular barriers surrounding Venice’s core areas – the primary island and its adjacent islets – effectively isolating them from the fluctuating lagoon waters.
This method could offer robust protection against sea level increases of up to 6 meters. However, the researchers caution that it could severely disrupt the city’s ecological relationship with the lagoon and fundamentally alter its characteristic ambiance, potentially impacting its cultural significance and tourism appeal.
Estimates for the implementation of this option range from €0.5 billion to €4.5 billion.
The Closed Lagoon Strategy
An alternative strategy involves the complete enclosure of the lagoon. This would be achieved by elevating the barrier islands and permanently damming the lagoon’s inlets with structures reaching approximately 5 meters in height.
This approach presents several advantages, notably its capacity to shield the city from sea level rises of up to 10 meters.
While this strategy would preserve Venice’s historical monuments, residential areas, and tourism sector, it would come at the cost of its unique lagoon ecosystem, a vital component of its historical identity.
Furthermore, this would effectively conclude Venice’s role as an active maritime port. This is also one of the more costly options, with projections from the researchers indicating a minimum expenditure of €30 billion.
A significant challenge associated with this option would be the prevention of water stagnation, necessitating a permanent pumping infrastructure to avert environmental degradation.
The End of an Era for the Floating City
The final proposed solution entails managed retreat: the systematic relocation of Venice’s inhabitants, its irreplaceable monuments, and its architectural heritage, effectively signaling the cessation of the ‘floating city’ era.
This undertaking would be monumental and emotionally taxing, carrying the highest associated cost of €100 billion. This figure encompasses not only the substantial expenses of relocating cultural artifacts but also compensation for residents displaced from their ancestral island homes.
This scenario would also permit the lagoon’s ecosystem to succumb to the consequences of deeper, warmer, and more saline waters driven by sea level rise, the ultimate effects of which remain uncertain.
An Unpredictable Trajectory
Balancing the imperative to protect Venetian heritage, culture, and the lagoon’s ecological integrity against the financial investments required presents a complex challenge. However, these cost estimates provide policymakers and residents with a clearer understanding of the available pathways forward.
“Given the profoundly inadequate international endeavors to curtail greenhouse gas emissions and the inherent inertia of sea level rise, it is imperative to seriously consider transformative strategies for the city of Venice and its lagoon,” the researchers stated.
“Under a high-emission trajectory, and assuming no additional adaptive measures are taken, the current open lagoon strategy is projected to become insufficient before the conclusion of this century.”
At this juncture, the implementation of encircling dikes or comprehensive barrages appears to be the most viable path. Nevertheless, the research team emphasizes the urgent need for proactive planning by policymakers and communities, as large-scale engineering projects of this magnitude can require up to fifty years from conception to execution.
