Category Environment

Last month’s flooding is attributed to a combination of factors including strong winds, heavy rains, high tides, which were pushed into Venice by southerly winds. Besides, rising sea levels make the city built amid a system of canals even more vulnerable to inundation.

The sea level around Venice has been rising steadily for decades and it has been attributed to climate change. Globally, the mean sea level is now estimated to be more than 20 cm higher than it was a century ago. Studies show that sea level is still rising 2.4mm a year along Venice. Some estimates suggest the Mediterranean Sea levels will rise by five feet by the end of the century, which could cause the city to flood twice daily. Currently, Venice experiences flooding about four times annually.

Further, the soft and the shifting geological terrain of the city has made the ground level sink gradually by an estimated one millimetre a year. Local industries around Venice make things worse by pumping groundwater from the aquifer under the lagoon.

Because of the combined effect of the city’s terrain and the rising of the sea, the water is now 30 cm higher against the buildings than it was when record-keeping began in 1873.

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Acqua Alta or ‘high waters’ is a seasonal phenomenon in Venice. The term is used to refer the exceptionally high tides that occur in the northern Adriatic Sea. The peaks reach their maximum in the Venetian Lagoon and causes flooding in coastal cities Venice and Chioggia.

The phenomenon occurs annually in November and December, when seasonal winds drive strong high tides up canals, through drains, and into the streets of the city.

Venice, built on a cluster of small islands, has always lived with tides that usually create variations of around 50 cm in sea levels but which can sometimes be more extreme, such as the ones experienced last month.

Climate scientists note that exceptional tides – those over 4 feet – have become much more frequent in the past two decades.

Of the 20 exceptional tides recorded since 1936, more than half have occurred after the year 2000.

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Last month, Venice was hit by three back-to-back floods in less than a week. They sent waist-high water flowing through the Italian city, threatening its iconic Saint Mark’s Basilica and other historic structures. More than 85% of Venice was inundated. The flooding was second only to the waters that inundated the city in 1956, when levels crossed 6 feet.

Venice’s huge Saint Mark’s Square was submerged by more than a metre of water, while the adjacent Basilica was flooded for the sixth time in 1,200 years – but the fourth in the last 20 years.

The floods were primarily driven by the aqua alta, or high tides, which is an annual phenomenon here. But other factors such as climate change and sea level rise made it worse. Experts say that floods of such intensities could become frequent in the coming years.

What is a flood?

A flood is a natural event when an area gets submerge under water for a while. Some floods can occur suddenly and recede in no time. Others take days or even months to build and recede.

Floods can develop in many ways. Heavy rain is one of the major reasons. If it rains hard enough or long enough, low-lying areas get inundated. The flow exceeds the capacity of waterbodies such as rivers, lakes and oceans. When water overflows beyond their boundaries, it leads to flooding. Breach in dams can also cause flooding.

Storm surge – abnormal rise in seawater level during a storm caused primarily by winds – causes the sea to rush inland.

Floods are destructive in nature as huge amounts of water get discharged, leaving no time for evacuation. Sometimes, floods are triggered by other natural disasters such as earthquakes and tsunamis.

What makes an area susceptible to floods?

Any plain low-lying area adjacent to a river or lake is more likely to experience floods whenever the water level rises – for example, a coastal city or a city with a river running through it.
A place’s susceptibility to floods also depends on the capacity of the catchment areas the volume of water hat a river or canal can hold without overflowing. When the amount of rainwater exceeds this capacity, floods may occur.

What is Venice like?

Venice is situated on a group of 118 small islands that are separated by canals and linked by over 400 bridges. The islands are located in the shallow Venetian Lagoon at the head of the Adriatic Sea in Northern Italy. The whole city is an extraordinary architectural masterpiece. The lagoon and a part of the city are listed as a UNESCO World Heritage Site.

Picture Credit : Google