I’m lost again. I glower at my crumpled map and peer at the ageing street signs. Venice is not a city to be navigated, but a labyrinth of alleyways and canals to be explored. I abandon my map and begin aimlessly wandering the city’s 117 islands.
Away from the garish gondolas, flocks of tourists and pigeons I see artisan stores and restaurants squeezed into the tiniest street corners. The aroma of leather, wrapped around feet and facemasks, is arousing. Even more magical, are the hundreds of bridges and waterways that connect Venice. But, beauty can be deceiving. Venice is under threat by its major attraction: water.
Rising sea levels could force locals to permanently replace their bespoke leather shoes for gumboots. “The survival of Venice and its lagoon is seriously questioned under the Intergovernmental Panel on Climate Change global sea level rise scenarios,” says Alberto Troccoli at CSIRO in Canberra, Australia.
According to Shimon Wdowinski at the University of Miami in Florida, over the twentieth century the upper Adriatic Sea, which cradles Venice, rose by 11 centimetres. “It is forecasted to be higher in the 21st century,“ he says. Climate models predict that the Sea will rise by 15 to 20 centimetres by the end of the 21st Century.
Worse still, while the sea encircling Venice rises, the city sinks. Earlier this year, Wdowinski and his colleagues used data from GPS and satellite radar to reveal that Venice sank an average of one to two millimetres per year between 2000 and 2010 . The subsidence is caused by the soil beneath the city compacting and dragging Venice down. According to Wdowinski, Venice is likely to continue sinking into the future. The team also uncovered that Venice is tilting slightly to the East, because the Adriatic plate, which Venice sits atop, is diving beneath the Apennines plate.
Heartbreakingly, storm surges also threaten these islands. During astronomical high tides, driven by the moon’s gravitational force, water reaches a maximum of 85 centimetres above sea level, which is just below Venice’s lowest points. But, storm surges can tip the balance and push floodwaters over large portions of the city.
These storms are driven by low pressure systems from the Atlantic, which allow sea levels to rise and strong south-easterly winds to blast the city. When combined, these forces create storm surges, pushing water toward Venice and leading to very high water conditions, locally dubbed “Aqua alta”. Many scientists believe that Climate Change will bring more frequent and severe storms to the embattled ‘City of Water’.
But last year, Troccoli and colleagues found something surprising. Combining data from observations of previous storms and models mapping Venice’s climate, the team calculated that storm surge events were likely to decrease by thirty percent by the end of the century. It’s possible that over the next few decades the low pressure systems may move away from Venice, and towards northern Europe, says Troccoli. “When we published the work, it raised a bit of controversy,” he says. However, the debate is not over. Uncertainties, such as the rate of ice melting in the Arctic and its effect on the Venetian climate, means that no one can be sure of Venice’s future climate.
Meanwhile, Italian authorities are developing an intricate series of floodgates, called the MOSE project, to reduce flooding in Venice. We can only hope the project will keep the city dry, at least in the short term. “Venice is a treasure, we don’t want to lose a city like that,” says Troccoli.
(Originally Published in New Scientist Magazine‘s Aus/NZ Travel Section)