Plants help combat urban heat islands

A team of American and Swiss researchers studied which factors best reduce temperature differences between cities and their surrounding environments. Their results could help urban planners keep cities cool.

Urban heat islands are a phenomenon where the temperature in a city is markedly higher than in the surrounding rural area. Under certain conditions, green spaces can help combat this effect.

Researchers from the Federal Institute of Technology (ETH) in Zurich, Princeton University and Duke University set out to determine how the temperature difference between cities and the surrounding countryside can be lowered. Using data from 30,000 cities worldwide and their surrounding environment, they found that the solutions differ depending on the regional climate.

According to an ETH Zurich press release, the urban heat island effect is more pronounced the larger the city and the more rainfall in that region. A city surrounded by a desert, like Phoenix, could achieve cooler temperatures with only a few green spaces, whereas a city surrounded by tropical forests, such as Singapore, would need far more green spaces to reduce temperatures. Cities located in tropical zones would require other cooling methods to be more effective, such as increased wind circulation, more use of shade and new heat-dispersing materials.

“There is no single solution,” said Gabriele Manoli, former postdoc with the Chair of Hydrology and Water Resources Management at ETH Zurich and lead author of the recently published.

City-specific solutions to reduce temperatures “will require additional analysis and in-depth understanding of the microclimate”, he said, adding that “such information, however, is based on data and models available to city planners and decision-makers only in a handful of cities, such as Zurich, Singapore or London”.

Image credit: Hector Argüello Canals via Unsplash

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