Examination of 28 heavily populated cities in the United States showed that all of them – in less or less degrees – are collapsed, including those located far from the coast. One of the main reasons is intensive groundwater extraction.
“As the cities will grow, we will observe how more and more of them are expanding to collapsing areas,” says the main author of the publication in the journal Nature Cities, Leonard Ohenhen from Lamont-Doherty Earth Observatory, Columbia Climate School.
“Over time, this soil settlement can cause infrastructure stresses that will cross its security limits,” he alerts.
Scientists remind you that the rapidly collapsing coastal metropolises, such as Jakarta, Venice or New Orleans, have already attracted a lot of attention, and numerous studies have shown that many places on the east coast of the USA, as well as in other regions are also settled.
However, most studies were based on relatively rare data dispersed in large areas, which only allowed to outline the general image.
Now, analyzing all cities in the USA about a population exceeding 600,000 residents, experts used the latest satellite data for mapping vertical movements of the Earth with an accuracy of up to one millimeter, in a net with dimensions of only 28 square meters.
In this way they discovered that In 25 out of 28 cities studied, at least two -thirds of their area are settled. In total, about 34 million people live in endangered areas.
Houston turned out to be the fastest collapsing city – over 40 percent. Its surface settles at a rate exceeding 5 millimeters per year, and 12 percent It falls twice faster. At some local points, settlement reaches up to 5 centimeters per year.
Two other cities in Texas – Fort Worth and Dallas – not much inferior to the leader.
Other places with local quick settlement zones include around the New York Laguardia airports and some areas of Las Vegas, Washington, DC and San Francisco.
Researchers also analyzed data on groundwater collection in areas affected by settling. They determined that for 80 percent Settlement corresponds to the consumption of water for the needs of people.
This phenomenon usually occurs when the water is pumped out of aquifer composed of fine -grained sediments. If such a layer is not supplemented, the spaces previously filled with water may ultimately collapse, leading to the density of sediments deep in and settling the surface. In Texas, this problem is further deepened by extracting oil and gas.
It does not seem to improve. Researchers say that a further increase in the population and water consumption, in combination with drieds caused by climate change, will probably lead to the residence phenomenon in the future.
Natural forces also work in places. For example, the burden of a huge ice sheet, which to about 20 thousand years ago, he covered a large area of the central part of North America, caused that the earth on its outskirts rose upwards – just like in a balloon, when the air was squeezed from one part to another. Even today, despite the fact that the ice has long melted, some of these discharge are still at a pace of 1 to 3 millimeters a year. Among the cities affected by this process are New York, Indianapolis, Nashville, Philadelphia, Denver, Chicago and Portland.
In addition, even the weight of buildings itself can have a noticeable impact. One of the studies from 2023 showed that over a million buildings in New York exert such great emphasis on the ground that it can contribute to the settlement of the city – scientists draw attention.
Other, newer study showed that some buildings in the Miami region are sinking partly due to changes in the ground caused by the construction of new facilities near them.
The new study also showed that eight cities – New York, Chicago, Los Angeles, Phoenix, Houston, Philadelphia, San Antonio and Dallas – brings together over 60 percent. population living in collapsing areas. Importantly, over 90 serious floods have taken place in these eight cities since 2000, probably partly caused by the lowering of the area.
Scientists also found that in some cities there are differences in the movement of the area – neighboring areas collapse at a different pace, and some of them settle while others increase. This upward movement can be caused by rapid supplementation of groundwater near rivers or other water sources.
The thing is, if the entire urban space moves up or down evenly and in the same pace, the risk of stress in the foundations of buildings and other infrastructure is minimal. However, when the structures are exposed to uneven vertical movements of the soil, they may be dangerous.
As scientists explain, in contrast to the threats associated with the settlement of the area caused by floods, where the risk occurs only when the rapid setting rate of settling reduces the area below the critical level, damage to infrastructure caused by settlement may occur even with small movements of the ground.
Although only about 1 percent The total area of the Earth in 28 tested cities is located in zones, where differential movements can affect buildings, roads, railway lines and other infrastructure elements, these areas usually lie in the most densely built -up city centers and currently there are about 30 thousand. buildings.
The most endangered cities in this respect are San Antonio, Austin, Fort Worth and Memphis.
It is difficult to assess the exact risk for specific constructions. Earlier study of 225 buildings cited by scientists collapsed in 1989-2000 showed that only in 2 percent. Cases were a direct cause was the collapse of the land. However, causes 30 percent Such events were considered unknown.
Researchers sum up that cities should use new information to focus on solutions. They claim that in many places floods can be softened by lifting the area, improving drainage systems and introducing green infrastructure, such as artificial wetlands.
Cities at risk of tilting buildings can also focus on modernizing existing structures, taking into account the movements of the Earth in building codes and limiting new construction investments in the most endangered areas.
“Instead of just saying that it's a problem, we can react, solve it, relieve the effects and adapt,” says Dr. Ohenhen. “We have to go to solutions.”
Marek Matacz (PAP)
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