During the nighttime, it is hotter in the city than in nearby suburbs or the countryside. But just how much hotter differs between cities. Researchers from the MSE2 (CNRS / MIT) international joint research laboratory and the Centre Interdisciplinaire des Nanosciences de Marseille (CNRS / Aix-Marseille University)1 have shown that the determining factor is how cities are structured: more organized cities, like many in North America with straight and perpendicular streets, trap more heat. Conversely, cities that are less organized, like those founded long ago, shed heat easily. The team's findings, published in Physical Review Letters (March 9, 2018), suggest new directions to explore for optimal urban planning and energy management.
Urban heat islands (UHIs) are created when the air temperature rises higher in cities than in the surrounding suburbs and rural areas. In the US, this phenomenon affects 80% of the urban population. In populated areas, UHIs can lead to greater energy consumption (to power air conditioning, for example), more air pollution, a lower quality of life, and poorer health. Some cities have applied strategies to limit UHIs—including the addition of more green spaces—but the environmental and economic impact of heat islands, at a national or even regional scale, has still barely been quantified.
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