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Paris eyes vegetation to beat the urban heat

FRANCE 24 screengrab

Paris authorities have been implementing a strategy to use increased vegetation to beat the urban heat effect caused by overcrowding and land surfaces covered by asphalt.

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With the mercury soaring to 42 degrees Celsius, Paris authorities are turning to trees for a cool-off solution.

Trees have this great characteristic of being evapo-transpirators: they absorb water from the soil through their roots, transmit it through their trunks, branches and leaves, where it escapes through pores. When it escapes, the water cools the ambient air,” explains Olivier Papin, an environmental engineer.

With his infrared camera, Papin measures the differences in temperature in direct sunlight, and under the shade of the surrounding trees.His aim is to map the capital's hottest points.

“You see, the bitumen road in the sunlight rises up to 50 degrees Celsius. But when in the shade, it cools down to 35,” he explains.

The lack of vegetation, coupled with land surfaces covered with construction material such as bitumen and asphalt, results in a phenomenon known as the urban heat island, which makes cities hotter than neighbouring rural areas.

"The fact that underneath [the roads], you have dense concrete only make things worse. It acts like a giant heat reservoir, and when night falls, all the heat that has built up [during the day] is released in the atmosphere,” explained Julien Bigorgne, an engineer at APUR (Atelier Parisien d’Urbanisme).

Engineers recommend the streets' coating be replaced by cobblestones, porous concrete or stabilised soil, a mix of sand and gravel, mostly used in parks.

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