Venice is often flooded due to its unique geographical location on a lagoon composed of many small islands, combined with rising sea levels due to climate change. Furthermore, the city is gradually sinking due to land subsidence, worsened by human activity and groundwater extraction.
Venice is built in the middle of a lagoon, a coastal space where the sea and land constantly mix. Its depth is very shallow, often less than two meters, with muddy bottoms that are not very solid and change all the time due to tides and currents. These permanent movements of water continuously shape the islands and canals that make up the lagoon. Venice has developed on more than a hundred small islands, separated by a maze of natural and artificial canals. Sandbanks (barrier islands) separate the lagoon from the open sea, but they are unstable and evolve regularly over time. This fragile configuration naturally makes the city vulnerable to flooding, especially when certain weather phenomena stir the waters a bit more.
Climate change is causing a global rise in sea levels, primarily due to two main phenomena: the massive melting of glaciers and polar ice caps, and the thermal expansion of water. Specifically, as temperatures rise, water warms and expands: as a result, it takes up more space and sea levels gradually rise. Venice, situated almost at sea level, feels this rise particularly acutely: just a few more centimeters are enough to turn a simple high tide into a genuine flooding problem. Over the past century, global sea levels are estimated to have risen by about 20 cm and this trend is accelerating. So, for a city like Venice, every centimeter matters.
The city of Venice rests on a thick layer of loose sediments, such as clay and sand. Not very stable. Over time, these sediments gradually compact under the weight of constructions, leading to a natural subsidence of the ground, which is called subsidence. It is a slow but continuous phenomenon, amplified for decades by the excessive pumping of groundwater for certain industrial uses. The concrete result: the city is slowly sinking. For about a century, Venice has lost nearly twenty centimeters in some areas, which significantly increases its vulnerability to flooding, especially when combined with rising sea levels.
Human interventions have significantly altered the Venice lagoon. For example, the construction of deep canals to facilitate navigation for large boats has disrupted the natural movement of tides. As a result, water flows more rapidly and enters the lagoon more easily, increasing the risk of flooding. At the same time, industry has caused excessive pumping of underground aquifers during the 20th century, which has accelerated the subsidence of the ground. Intensive urbanization has also reduced the natural areas capable of absorbing water, making the city even more vulnerable.
The mobile barriers of the MOSE project, that famous system meant to protect Venice during high tides, regularly face technical issues: parts that corrode, mechanisms that break down, or skyrocketing maintenance costs. It's not all rosy on the ecological front either: the constant opening and closing of these massive metal structures seriously disrupts the natural marine balance of the lagoon. Moreover, even when everything works perfectly, the barriers are only effective up to a certain level of flooding, beyond which they are likely to fail, especially in the face of extreme phenomena exacerbated by climate change. Add to that a delicate planning process (opening too early or too late is risky) and frequent delays, and you quickly realize that these solutions, although ambitious, are far from sufficient to ensure a peaceful future for Venice.
Despite the installation of the MOSE (Experimental Electromechanical Module) flood prevention system, Venice continues to occasionally experience flooding events. Its current limitations are prompting experts and authorities to consider complementary and sustainable solutions.
The famous Basilica of Saint Mark regularly suffers from the destructive effects of saltwater: repeated flooding seriously threatens its millennia-old mosaics, prompting specialists to consider various innovative projects for its conservation.
The iconic canals of Venice are regularly maintained through dredging to remove accumulated sediments. This complex process allows boats to navigate efficiently while ensuring better flood management and maritime flow in the lagoon.
The phenomenon of 'acqua alta' ('high waters') in Venice is not recent: historical records show that it was already mentioned in texts dating back to the Middle Ages. However, these floods have become more frequent and severe in recent decades.
The Venetians have adapted through various methods: the installation of temporary walkways during floods, the elevation of certain buildings, the use of pumps to evacuate water, as well as the adoption of an alert system that allows for forecasting and anticipating episodes of acqua alta.
Repeated flooding causes a gradual deterioration of Venice's historic structures: erosion of stones, corrosion of metal elements, and weakening of foundations. In the long term, these phenomena seriously threaten cultural heritage and require regular and costly restoration interventions.
Venice mainly experiences its flooding phenomena, known as 'acqua alta', between October and March. During this period, the combination of high tides, strong winds (such as the sirocco), and frequent rainfall contributes to these flooding events.
Venice is sinking due to several factors, including the extraction of fresh groundwater (which has now been reduced), the natural settling of the sediments on which the city is built, and the considerable weight of its historical buildings. This phenomenon of subsidence, combined with the global rise in sea levels, increases the risk of flooding.
The MOSE system (Experimental Electromechanical Module) is a device made up of mobile barriers placed at the three entrances of the lagoon. When the tide exceeds a certain critical threshold, these barriers rise to prevent water from entering and protect Venice from flooding. Despite its potential effectiveness, MOSE faces regular technical and economic challenges.
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