The sinking cities

The sinking cities

Of the 48 most populated coastal cities in the world, 44 are sinking into the ground faster than the waters are rising. The total is debatable, depending on the urban region that is calculated, but it reminds us that several of these metropolises have very large infrastructure works on the horizon, if they want to protect their most at-risk neighborhoods.< /p>

Roughly, sea level rise is currently estimated at 3.7 millimeters per year — a figure that varies from one region of the world to another. In comparison, the authors of this new study estimate that between 2014 and 2020, the median rate of “sinking” or subsidence of the ground varied from 1.1 mm for the cities least at risk to 16.2  mm — and some of the most at-risk cities even have neighborhoods that have exceeded 20 or even 30 mm per year during this time. Among them are Tianjin, China, and Ahmedabad, India. Not far behind are Ho Chi Minh, Vietnam or Jakarta, Indonesia. But overall, 44 of the 48 cities surveyed are above the 3.7mm limit.

There where the results of these researchers, published on September 12 in Nature Sustainability, are disputed, it is in the choice of the territories to be taken into account. They chose the entire territory of the cities in question; others would have recommended calculating only the portion located a short distance from the shore.

In any case, the The causes of this “sinking” are the same everywhere: pumping of underground water, extraction of oil or gas, compaction of sediments under the weight of the most massive buildings.

In the jargon of geologists , this process is called subsidence. It means that, where there are not flood barriers high enough, or rainwater drainage systems much more efficient than today, entire neighborhoods will increasingly underwater during the next major storms.

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