Half of Venice set to be flooded
Tourists wade across Saint Mark's square in 'acqua alta'31 January, 15:59
A third of Venice was already under water as waters passed the 125-cm mark amid an unrelenting wave of rain across Italy.
It was the fourth straight day the 'acqua alta' or high water went over the 110-cm level that covers low-lying areas like St Mark's Square, forcing tourists to wade across the landmark piazza.
If the acqua alta hits the forecast mark, pontoon walkways will have to be put up in St Mark's and other famous places. In the high-tide season, which lasts from autumn to spring, water routinely spills over the city's banks, flooding its streets and squares and occasionally threatening to set new records when the skies open, as they have done this week.
The highest-ever acqua alta came during the great flood of 1966, at 194 cm, when waters caused huge damage.
Levels of 120-130 cm above sea level are quite common in Venice, which is well-equipped to cope with its rafts of pontoons.
But anything much higher than that risks swamping the city and washing all the walkways away, as happened in December 2008 (156 cm), December 1986 (158 cm) and December 1979 (166 cm).
The causes of acqua alta are both natural and man-made.
Decades of pumping groundwater caused significant damage to the delicate foundation before the practice was called off.
Weather experts say the high-water threat has been increasing in recent years as heavier rains have hit northern Italy.
Other possible explanations for the phenomenon include the sea floor rising as a result of incoming silt and gas extraction in the sea off Venice undermining the islands.
According to a recent study, plate tectonics are also to blame as the Adriatic plate is sliding beneath the Apennine Mountains, causing the area to drop in elevation.
Scientists have conceived various ways of warding off the waters since a catastrophic flood in 1966 and a system of moveable flood barriers called MOSE is near completion after years of controversy.