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Venice faces rising flood risks in the decades ahead

Venice faces rising flood risks in the decades ahead
New forecasts suggest Venice may need stronger defenses to safeguard the city against sea level rise and increasing flood risks. File Photo by EPA-EFE/ANDREA MEROLA

Sept. 1 (UPI) -- According to a new assessment, Venice is likely to face rising flood risks through the end of the 21st century.

For the study, published Wednesday in the journal Natural Hazards and Earth System Sciences, researchers in Italy ran simulations using the most up-to-date climate and sea level rise models.

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While storms and precipitation can influence flood risk projections, sea level rise is the main driver of flood risk in Venice and other coastal cities. Unfortunately, long-term sea level rise projections feature a significant amount of uncertainty.

Different emissions scenarios can yield different sea level rise outcomes. Even under stable emissions scenarios, uncertainty about ice sheet dynamics in Antarctic and Greenland persists.

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"For a projection to be useful, it must be well constrained," study co-author Davide Zanchettin said in a press release.

"There are important feedbacks in the climate system, for instance related to polar ice sheet dynamics, that we need to understand and better simulate to make more reliable projections," said Zanchettin, an environmental scientist at the Ca' Foscari University of Venice.

Though long-term flood risk is primarily driven by sea level rise, individual flooding events in Venice have historically been triggered by sirocco winds, which can fuel destructive storm surges.

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Even small changes in sea level rise can increase the odds that sirocco winds will trigger coastal flooding.

"When you are this close to the upper limit of the tidal range, any meteorological event can be hazardous and cause an extreme flood," said study lead author Piero Lionello, an environmental scientist at the University of Salento. "Small increases can have a large impact."

In the short-term, the authors of the new assessment suggest the city's vulnerability to flooding is largely dependent on the success of the MoSE coastal defense system.

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When forecasts predict a surge in water levels, a series barriers can be closed to mitigate flooding.

"The MoSE system will be operated on the forecast," said co-author Georg Umgiesser, also a researcher at Ca' Foscari. "If the forecast is wrong, the operation of the MoSE becomes wrong -- and that is very important both economically and ecologically."

By using a variety of climate models to constrain future sea level rise projections, researchers hope to reduce the uncertainty surrounding long-term flood risk forecasts.

If sea level rise increases dramatically, researchers suggest Venice may have to develop a more robust sea level defense system to supplement MoSE.

"Sea level is a nasty beast; we could stop global warming completely by stopping the use of fossil fuels and the sea level would continue to rise in spite of this, though at a much reduced pace." Lionello said.

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"But we have the information with studies like these to identify the future risk to coastal cities like Venice. Although we don't know exactly when, the present evidence is that we will need to change our adaption strategies. It's clear that we need to be prepared to act," Lionello said.

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