Why is Venice drowning?
On November 17, 2019, the Italian city of Venice got flooded for the third time in a week because of an ‘exceptional’ storm tide. The frequency of such events in the city has increased alarmingly in the past several decades, indicating an impact of human-caused global warming.
Italian experts identify an exceptional storm tide when the height of the water during a sea surge caused by a storm crosses 1.4 metres. This rise in sea-level can flood around 50 per cent of Venice.
Such events have happened in the city only 22 times in the past 147 years since records began, according to data from the Institution for Forecasting and Reporting Tides. They occurred only once from 1872 to 1950, nine times between 1951 and 2000, seven times from 2001 to 2017 and five times in the last two years. The last three have come within the past week.
The Global Forecasting System data shows that there have been regular storms close to the Italian coast and strong winds in general since November 10 which are being fed by larger cyclonic circulations over continental Europe.
Apart from Venice, these storms and winds have caused heavy rainfall in many regions of Italy causing floods. The country had been affected by historic flooding last year as well which had killed 36 people.
All the contributing factors for the occurrence of exceptional storm tide events and associated flooding, except for high tides, are human-caused and are related to either development or global warming.
The flooding is primarily caused when sea water is vertically pushed from the Adriatic Sea into the Venetian lagoon due to strong winds during a storm. Such a high water event is known as an Aqua Alta.
The flooding is more severe if the storm is intense and coincides with a high tide event. This is what caused the second-highest storm tide of 1.89 metres ever recorded in Venice on November 12, or perhaps many of the 21 other exceptional storm tides.
While global warming is causing intense storms more frequently and making sea-levels rise in general, the city is also sinking due to construction activities, fresh water pumping from underground aquifers and coastal erosion increasing the probability of such events in the future.
“Sea-level rise will increase the frequency of extreme sea-level events, which occur for example during high tides and intense storms,” said the press release by the Intergovernmental Panel on Climate Change (IPCC), when it released its Special Report on the Ocean and Cryosphere in a Changing Climate in September this year.
“Indications are that with any degree of additional warming, events that occurred once per century in the past, will occur every year by mid-century in many regions, increasing risks for many low-lying coastal cities and small islands”, the IPCC further stated.
For Venice this week, the events have occurred thrice in week along with a long-term sea-level rise of 25 centimetres between 1912 and 2012, which makes the city’s climate adaptability not a future project but a current predicament.
To counter its extreme vulnerability to storm surges and flooding, Venice has been making efforts since 1966 when the highest storm tide of 1.94 metres was recorded in the city, killing 100 people and causing damage to historical monuments and art works, according to a report by Scientific American.
None of these efforts came to fruition until the implementation of project MOSE in 2003. Under this project, inflatable gates will be built along the coastline to protect from storm surges during storms but the project, which was to be completed in 2012, has been currently delayed by 10 years and is set to be functional by 2022.
It has also courted controversy due to cost overruns of up to three times of the initial and now stands at $6.3 billion.
And if the world fails to cut down on its greenhouse emissions in the next few decades, even this money will be wasted as MOSE’s inflatable gates will be no match to the intense storm surges of the future and general sea-level rise of upto 1.1 metres, as the water will then find new ways of seeping into the city.