2023-07-11 09:20:48
Human activities sometimes have effects of which we are still unaware. About our cities, we learn today from researchers. A consequence of a warming that we did not necessarily suspect.
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“Underground global warming is a silent danger. » It is the belief of Northwestern University researchers (United States) following work they have just published. “Under the effect of temperature variations, the ground deforms. And no existing civil structure or infrastructure is designed to withstand these kinds of variations. » Even if the causes are completely different, there is no need to live in Venice, therefore, to live in a city that threatens to collapse.
Global warming poses a ‘myriad of risks’ for cities: here are some
We already knew that, as a consequence of human activities, the atmosphere is warming up. The ocean too. But the ground? According to the researchers, it is also warming up. By diffusion of heat from the buildings of our cities and the underground transport infrastructures. Studies have estimated this warming at something between 0.1 and 2.5°C per decade for the shallow subsoil. It is enormous !
Researchers already know that this underground global warming causes ecological problems – risks of groundwater contamination, for example – and even health problems – an upsurge in cases of asthma or heatstroke. They now know a little more regarding its effect on civilian infrastructure.
Ancient cities most in danger
For three years, the Northwestern University team patiently collected data using more than 150 sensors installed throughout Chicago (United States). Including to witness sensors buried in a green space on the edge of Lake Michigan. The researchers note that temperatures underground often appear up to 10°C higher than those below the park. As for air temperatures in underground structures, they can be up to 25°C higher than the ground temperature “undisturbed”. The phenomenon would be common to all dense urban areas of the world.
In another stage of their work, the researchers simulated underground global warming up to 2051 and how the ground will deform in response. Because when the heat diffuses towards the ground, it exerts significant pressure on the materials. Some, like clay, contract and others, like limestone, expand. Models show that Chicago soils can thus swell up to 13 millimeters or sink no less than 8 millimeters. With the risk of seeing the appearance of cracks or settlements that compromise the performance of the structures. But “not enough to cause a building to collapse suddenly”reassure the scientists.
“When the heat diffuses towards the ground, it exerts significant pressure on the materials”
Researchers at Northwestern University still believe that the oldest buildings, in the oldest cities like our European cities, might be seriously impacted. They nevertheless warn once morest the temptation to want to cool underground structures. This would consume energy unnecessarily. While there are technologies that might recover waste heat and return it to buildings for heating. Or that it would be enough to install thermal insulation on buildings in order to minimize the amount of heat that penetrates the ground.
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