VENICE—Living these days inside their homes to stop the spread of the coronavirus, Venetians have discovered a silver lining in an empty city suddenly free of polluting tourist boats. The water in the legendary canals is clear, unlike anything they’ve seen in decades.
Lidia Feruoch, president of the Venice branch of Italy’s largest environmental group, Italia Nostra, rejoiced at watching “cormorants dive into the canals to catch fish because the water in the lagoon has become transparent again,” she said in a recent interview. She hopes the end of the pandemic will free Venice from a “tourism monoculture” that brings 27 million visitors a year to this city of 50,000.
Still, Feruoch and Don Roberto Donadoni, parish priest of the Basilica of San Marco, remain mindful of the city’s other existential threat, climate change, a preview of which they saw in the dark and churning waters of November, when extreme flooding from heavy rains and high tides swamped Venice and reached a level a few scant centimeters below that of the legendary 1966 flood.
If the world can’t radically reduce its carbon footprint, climate models show that sea-level rise is most likely to inundate Venice by 2100. Either radical steps to slow global warming must be taken by world leaders, or some special fix for Venice needs to be devised and implemented. To date, no one knows what that would be.
The current solution, a vast, 6 billion euro network of flap gates designed to wall Venice off from the roiling water and protect the city from heavy rains, high tides and flooding, is far more problematic than social distancing during the pandemic.
Most environmental scientists and engineering experts believe the Electromechanical Experimental Module, or MOSE, is probably obsolete already, despite being years away from completion, assuming the complex underwater technology ever works. It was designed 20 years ago when the projections for sea level rise throughout the century were not nearly as dire as they are now. They are only expected to grow as ice melts in Greenland faster than anticipated.
Their fears echo those of environmentalists in New York about a giant system of retractable seagates that the U.S. Army Corps of Engineers is studying as a way to protect Manhattan from another storm surge like Hurricane Sandy in 2012.
Both the Italian and American projects raise fundamental questions about the ability to hold back the rising tides in coastal cities worldwide.
Piero Ruol, a professor of Maritime Construction at the University of Padua, said even best-case scenarios for carbon reduction would result in enough sea-level rise to require that the MOSE stay shut over six months a year, which would essentially kill the Venice lagoon environmentally.
“Therefore, the MOSE can not be considered a solution that ‘lasts forever’ for protecting Venice from flooding,” he said, “and it is time to think of new solutions for solving this delicate conundrum, in the face of climate change.”
The salt left behind after the high water receded last November had just stopped seeping out of the walls and benches of Santa Maria del Giglio, leaving the church benches a stark white. Many of the pews had swollen as the water penetrated the wood, and now they were crumbling.
As Father Donadoni walked along the church’s nave, the traces of the flood were still vivid.
“On the evening of Nov. 12, we were preparing, like all the other times, for fairly normal high water, acqua alta,” he said. “They had warned us that it would reach 140 centimeters but, as we know, the events didn’t bring high water but, instead, what we call ‘large water,’ which caught us unprepared. The Scirocco winds brought the water from 140 to 187 centimeters in a few minutes.”
The high water mark was second only to the 194 centimeters measured during the 1966 flood. Extreme flooding from rains and high tides used to be rare, but it has been occurring with increasing frequency over the last several decades.
From 1923 to 2000, only 10 cases of “exceptional tides”—when the tide is more than 140 centimeters above mean sea level—occurred in Venice. But since 2001, there have been 14 exceptional tides, with the last one occurring that night in November.
“The water could be seen rising within a few minutes and we could only watch with impotence because there was nothing we could do, and we only prayed that the wind would stop,” Donadoni said. “When the large water crested at 187 centimeters and the message came that it was over, a cry, which was almost a cry of relief, was heard throughout the square.”
The vast lagoon that surrounds Venice and connects to the Adriatic Sea has been the subject of human hydrologic efforts since the 15th and 16th centuries. Until the time of Napoleon, all modifications and excavations were managed by a magistrate called the Magistrato alle Acque. The magistrate had to approve even minor excavations or “dighette” in the most remote parts of the lagoon.
This changed after the great flood of 1966 and the passage of a special law in 1973 that mandated the protection of Venice and its lagoon. The law has specific air and water quality requirements and contains provisions for the preservation of Venice’s historical, archeological and artistic environment.
The MOSE project was born from a ministerial commission established under the law in 1979. Three years later, the city’s Board of Governors approved the experts’ recommendation for the floodgate system, and the city has been pushing ahead with construction since then. The system was designed to defend Venice and its lagoon against water rising more than 110 centimeters above the mean sea level, but that meant it would not have kept all the floodwaters out last November.
Concerns over aesthetics and the environmental impact of such a system led to a decision that the floodgates, when inactivated, would not be visible. A total of 78 hollow steel barriers, each 30-meters wide, lie flat on submerged concrete foundations until they are filled with air, rising at a 45-degree angle to keep out flood waters. The gates are attached to the foundations by giant hinges.
The decision to conceal the gates underwater meant that most other potential interventions frequently mentioned in the media to counter flooding weren’t feasible. Among those with an unacceptable visual impact: a sluice gate plan with 22-meter pylons at each entrance to the lagoon.
“The MOSE is a very innovative system from an engineering point of view, although it still has some problems to be solved, and it will have very high maintenance costs, ranging from 50-100 million euros per year,” said Piero Ruol, a professor of Maritime Construction at the University of Padua.
Fabio Pranovi, an associate professor at the Ca’ Foscari University of Venice, voiced an even more basic concern, saying the MOSE has fundamentally changed the “co-evolution between inhabitants and the lagoon system.”
In October 2014, at Lido-Treporti, one of four ports allowing entry to the lagoon, the first four of the 78 gates were installed. But since then, the project, which should have been completed in 2016, has stalled and the projected completion date has been pushed back to 2022.
Currently, functional tests have been carried out, but the future of the MOSE is highly uncertain, given questions about the system’s experimental technology and maintenance requirements. Scandal has also engulfed the project, with numerous politicians accused in 2014 of misusing public funds and accepting bribes for awarding contracts.
When and if the MOSE becomes operational, the latest projections of the Intergovernmental Panel on Climate Change about sea level rise have made it clear that the giant gates might have to be closed far more frequently than previously imagined.
Annual mean sea level (MSL) is the average of the maximum and minimum values recorded in a year, and it has been increasing for a long time. Tide cycles in Venice last 12 hours: For six hours the tide grows and, after the climax, it drops. The tide comes in and out of the three vast inlets that connect the lagoon with the open sea.
While the tides are controlled by the moon’s gravitational pull, the ocean’s water levels are also influenced by weather. Low pressure systems make the water rise more than expected and high pressure systems make it drop more than normal; the north wind pushes water away from Venice and the south wind pushes water against the city.
The present annual mean sea level is 31 centimeters higher, on average, than the value computed in 1900, at the beginning of the last century. The largest increase occurred from 1930 to 1970 as a result of the combined effects of subsidence and sea level rise. After that period, and until 2008, the MSL was fairly stable, but then it again began increasing.
In 1900, only about one high water event occurred annually, while now there are five or six annual high water events. Similarly, the number of events with very low water levels has decreased over the same time period.
In the months before Italy became Europe’s first major casualty of the new coronavirus, the Venice flooding and the as-yet non-functioning MOSE had received wide attention as one of the world’s great object lessons on the potential threat of climate-related sea level rise.
Ruol said that storm surges, unlike normal tides, are not foreseeable in the long-term. “In addition to the lunar and meteorological influences, climate-related planetary sea level rise and the fact that Venice is slowly sinking about 2 millimeters per year compound the issue,” he said.
In 2018, Luigi D’Alpaos, professor of hydraulics at the University of Padua, reported in the journal Nature that an estimated sea-level rise of 50 centimetres, a level predicted by the latest Intergovernmental Panel on Climate Change (IPCC) report, would activate the MOSE’s gates and close the lagoon for up to 187 days each year by the end of this century, and occasionally for weeks at a time.
“This is a very important aspect from an environmental point of view,” Ruol said.
If the lagoon were to be closed off that long, there would be insufficient water exchange with the Adriatic Sea and a lack of oxygen throughout the lagoon. The effects of any prolonged closure on the ecological balance of the lagoon are currently under study by Pranovi’s research team.
“For a year and a half, we have been carrying out an assessment of how the water exchange will change once the MOSE has started operating,” Pranovi said. The gates could affect fish populations, some of which live and reproduce in the lagoon, and others of which only enter the lagoon to feed, he said.
Filippo Giorgi, a climatologist who from 2002 to 2008 was a member of the executive committee of the IPCC, said that its most optimistic scenario foresees global temperatures rising by about 1 degree Celsius by the end of the 21st century (compared to today’s temperatures) and a further sea level rise of about 40 centimeters, with a margin of error of 10 centimeters, compared to current levels.
“We must note that even under this scenario, the values of sea level increase up to the end of the 21st century and even beyond,” said Giorgi, who has contributed to the IPCC activities since the 1990s.
Under the most pessimistic, “business-as-usual” scenario, the planet would warm by about 4 degrees Celsius, with a sea level rise of 75 centimeters, plus or minus 20 cenimeters. “So let’s say from 55 centimeters to almost 1 meter,” he said.
And this estimate is likely to increase in the next IPCC report in 2021 because the ice in Greenland is melting much faster than earlier models indicated, Giorgi said.
“More worrying,” he said, “is that we still do not know exactly why. One of the theories is that pollution makes the Greenland ice darker, and being darker it absorbs more solar radiation and melts faster. The difference in temperature between the last glacial period, 20,000 years ago, and today is around 5 to 7 degrees, so we are talking about huge global warming values in 80 years, an unprecedented speed of warming.”
Climate change will also have a major impact on rainfall patterns as the jet stream shifts. In the Mediterranean area, the change will be much greater in summer than in winter, he said. Storms that would normally occur in the Mediterranean area and therefore also in Venice, will move further north, so Central and Northern Europe will receive more rain than they receive now according to the models.
But Southern Europe and the Mediterranean will receive less rain. This phenomenon is especially notable in the hot seasons of spring and summer. “In the Mediterranean, we will have much warmer and drier summers than today, on average up to 5 to 6 degrees warmer and with up to 20 to 30 percent less precipitation,” he said.
Giorgi pointed to the summer of 2003, with more than 35,000 deaths and 10 billion euros in agricultural losses attributed to unprecedented heat waves, as an example of what could become a normal summer. He said many summers will become very hot and dry, with almost no precipitation, and winters will be drier, too.
“Despite this,” Giorgi said, “when it does rain, it will rain very hard because the atmospheric and ocean temperatures will be higher, and this will give more energy and more water to the storm systems. In other words, we will move to a regime of less frequent but more intense rain, leading to increased risk of both flood and drought.”
Giorgi’s team recently carried out a study to determine what city today has a climate similar to what Venice will have in the future. “Based on the changes in temperatures and rainfall under the [business-as-usual] scenario, we found that the climate of Venice will be similar to the climate that today we have in southernmost parts of Italy or northern Africa,” he said.
Rome and Naples would have a semi-arid climate, while cities in southern Italy, such as Cagliari, Reggio Calabria or Palermo, would have a semi-desert climate.
“It is as if, climatically speaking, Italy would move about 1,000 kilometers to the south,” he said. “In short, 4 to 5 degrees Celsius of global warming means a total turmoil of the climate system, with major effects that are very difficult to predict. MOSE would probably always have to stay up, but it would not be sufficient to protect Venice.”
Vittorio Giambruni, a Venetian who has worked to help preserve the city’s historic residences, doesn’t see MOSE as a definitive solution, either. “MOSE is a highly advanced engineering solution but perhaps precisely because it is so sophisticated, it suffers from excessive delicacy, especially if we consider that it is located in salt water and that it will face extreme situations.”
The retractable gates of the MOSE are underwater and will require constant care. “Each module is 12 meters high and 30 meters wide, and therefore requires a huge amount of maintenance,” he said. “So the complexity of this work requires an organization that today is not present in this city.”
When Father Donadoni reached the end of the church’s nave, with the white salt coloring the walls and furnishings, he talked about how a few days after the flooding, the shutters of the shops opened again onto the Piazza San Marco.
“Even with the high tide having done so much damage in no time, we got back on track. There were people who after two or three days had already reopened their shops,” he said, describing a scene that will be repeated, at some point in the future, by the reopening after the coronavirus.
The church of Santa Maria del Giglio did not reopen until late January, which meant worship services had to be moved temporarily. “Parts of the confessionals, made of wood, have already rotted. We had to take the pews and bring them all to the presbytery, waiting for the situation to improve,” he said.
In those days just after the flood, the employees of the historic Rizzo bakery went around the city delivering bread to Venetians. Their shop was one of the few spared by the 187 centimeters of brackish water.
“We live with high water and live with it constructively; when it arrives, we equip ourselves to face it,” said Nicola Rizzo, owner of the bakery and a climate change skeptic, who saw the flood as an exceptional and isolated event. “The human side of the episode, important to remember, is that a few days after the exceptional tide and the disaster, the city had recovered and returned to normal.”
Father Donadoni doesn’t think the city will recover so swiftly from the pandemic. “After the flood, shopkeepers and citizens looked on everything that had been damaged but looked to tomorrow with optimism,” he said. “The coronavirus does not allow you to look toward the horizon because we do not know what will be there.”
The horizon for climate change is more distant. But for the “Floating City,” with sea levels rising inexorably and nothing able to entirely hold back the water, the damage could be even more catastrophic.
Top Photo Credit: Andrea Pattaro/AFP via Getty Images
Sara Moraca is an award-winning freelance science journalist based in Varese, Italy, whose writing focuses on issues related to climate change, ecology, and environment. Her work has been featured in National Geographic Italy, Wired, Corriere della Sera, and Nature.
Our journalism is free of charge and available to everyone, thanks to readers like you. In this time of crisis, our fact-based reporting on science, health and the environment is more important than ever. Please support our work by making a donation today.
电话:020-123456789
传真:020-123456789
Copyright © 2024 Powered by VatradeCoin Insights http://db.vatradecoin.cyou/