Flood Mapping: Rising Sea Levels Threaten Venice’s Future

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The fate of one of the world’s most treasured cities hinges on the performance of a mega-project scheduled to be fully operational later this year.

A system of flood barriers, located at three inlets that separate the Venetian Lagoon from the Adriatic Sea, is  designed to hold back the rising water and prevent Venice from being consumed by the sea.

Spread over 118 small islands separated by canals and bridges, Venice’s enchanting layout is also what makes the city prone to what Venetians call “acqua alta” or high water.

In recent years, the onset of more extreme weather caused by climate change has resulted in much more severe and frequent flooding, raising serious doubts about whether Venice – founded in the 5th century – can survive the 21st century.

To prevent the unthinkable from happening, city planners okayed the flood protection system, referred to as MOSE, which is an acronym for its full name in Italian and calls to mind the story of Moses parting the Red Sea.

 

Construction began in 2003, and will end up costing around €8 billion. The time and money required has limited the number of storm surge gates projects. London and Rotterdam have similar installations.

Venice’s barriers were first raised in October 2020, keeping the city mostly dry, despite an exceptionally high tide of 135 centimeters (53 inches). The gates have gone up dozens of times since, part of the testing phase expected to be complete by late 2023.

So far, the results have been promising. A bad storm in November 2022 led to heavy rainfall and high tides, but no major flooding in Venice.

Even routine rainfall often results in standing water across the city. The graphic below captures Venice in December 2022, with water (colored blue) clearly visible.

We generated this graphic using a proprietary algorithm that is designed to detect the presence of water when applied to synthetic aperture radar (SAR) imagery.

SAR is a satellite-borne instrument that works in any weather, day or night. This 24/7 capability is an obvious selling point when trying to document the flooding extent in the middle of a storm, such as the one that Venice endured in November 2019.

It was the city’s second-worst flooding event since records began almost 100 years ago. The world was stunned by images of famous sites, including Saint Mark’s Square, covered in feet of water. Water levels rose 194 centimeters (6.4 feet) above sea level, causing an estimated €1 billion worth of damage.

Of course, the true cost of what can be lost is immeasurable. The UN’s culture agency (UNESCO) lists Venice and its Lagoon as a World Heritage Site, in recognition of the city as an “extraordinary architectural masterpiece.”

Sadly, Venice isn’t alone when it comes to world treasures facing an uncertain future. All of the UNESCO-designated sites, totaling almost 2,000 and covering a land mass equivalent to the size of the United States, are vulnerable to climate change.


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