Capital Weather Gang

The many reasons Venice is flooding right now

The severe flooding in Venice Tuesday into Wednesday saw waters rise to the second-highest level on record, peaking at just over six feet, or 1.87 meters, in the historic city and popular tourist destination. This put the tide level behind only a flood in 1966. Tides of 55 inches or more are referred to as “acqua alta,” or high water, in Italian, and most such flood events occur during the winter, when storms prowl the Mediterranean.

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A man crosses St. Mark's Square on Nov. 13 in Venice.

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Tourists take pictures in a flooded St. Mark's Square in Venice on Nov. 13.

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A man stands in St. Mark's Square in Venice on Nov. 12.

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The historic flood event, which submerged large parts of the city, resulted in part from an unusually strong storm centered over the Tyrrhenian Sea, which caused high winds to buffet the city. These winds, known as sirocco winds, blow from the southeast from North Africa across the Mediterranean and up into the Adriatic Sea, which lies between the Italian Peninsula and Croatia.

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A storm system swirling across the Adriatic Sea on Nov. 12, helping to cause flooding in Venice.

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The long, relatively narrow and rectangular shape of the Adriatic Sea can amplify the effects of such winds by causing a seiche, or an oscillating water motion from one end of the sea to the other. The winds can have the effect of piling up water on the northwest side, where Venice is located. Because the winds can prevent the retreat of water from the northwest end of the Adriatic, much higher tide levels can be achieved in Venice compared with other parts of the Mediterranean, simply because of its geography.

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Partially submerged ferry boats in Venice on Nov. 13.

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People wade through water in Venice on Nov. 13.

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People walk across the flooded St. Mark's Square in Venice on Nov. 13.

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Tides high enough to flood the city used to be relatively rare, occurring every two to three decades. Now, though, they happen with increasing regularity, on the order of every five years or less. Of the top 10 tides in Venice’s history, half have taken place in the past two decades, and the most recent top five flood event occurred just last year.

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Pedestrians crossing St. Mark's Square after flooding on Feb. 6, 1974.

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People walk on a footbridge in Venice on Nov. 13.

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Although the storm was clearly a major cause of this particular flood, such events are becoming more damaging over time as sea levels increase because of human-caused global warming. In the case of Venice, the city — which was built just a few inches above sea level, is also subsiding, or sinking, over time, making sea-level rise even more of a threat.

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“This is a vivid picture of what’s going to happen at most coastal places in the future,” said Michael Oppenheimer, one of the authors of a recent Intergovernmental Panel on Climate Change report and a professor at Princeton University. He noted that while the flooding in Venice is due to a combination of subsidence and sea level rise, other coastal cities are facing damaging and routine flooding by 2050 from sea level rise alone.

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A man walks through a flooded St. Mark's Square in Venice on Nov. 13.

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A woman walks past a flooded cafe terrace in Venice on Nov. 13.

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Unlike most major cities worldwide, which have not yet decided how to gird themselves against the effects of sea-level rise, Venice is working on a multibillion-dollar project to keep floodwaters out and preserve the city. The project, known as MOSE, consists of a massive underwater floodgate system. However, it’s been mired in corruption and is not yet complete, leaving the city fully exposed. Even if it’s fully installed, it may not fully protect Venice from succumbing to sea-level rise and storm-surge-related flooding.

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The artwork by street artist Banksy in Venice on Nov. 13.

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Damaged books are piled outside the renowned Liberia Acqua Alta bookstore in Venice on Nov. 15.

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A flooded street in Venice on Nov. 15.

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Three men share a bottle of wine in a flooded street in Venice on Nov. 15.

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A woman wearing a wedding dress poses for an early morning picture in St. Mark's Square in Venice on Nov. 15.

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A room in the flooded Gritti Palace in Venice on Nov. 13.

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