Plant or Paint? The London rooftops transformed to combat heatwaves

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A study by climate researchers at University College London has found that green roofs planted on the top of buildings are effective at cooling temperatures during the day, but then go on to make the nighttime warmer. In London, many rooftops have been transformed to help cool the city down as temperatures soar. Some are covered in gardens and wildlife, while others are sprayed with white paint to help reflect the heat away. The researchers believe the latter are more effective when it comes to cooling down the city. Despite offering immersive views of the wider city skyline, the roof on top of investment bank Nomura in Central London is not accessible to the public or the building’s staff. The purpose of green roofs like this one is to help cool the temperature of the surrounding areas in cities, with added benefits like promoting biodiversity. Two common types of roof modifications are “cool roofs” and “green roofs.” “Cool roofs” include roofs which are sprayed on with reflective properties, like white paint, while “green roofs” are typically covered with plants. The green roof is classed as a biodiverse, bio-solar green roof, consisting of a mosaic of habitats including sedums, open ground and longer meadow-type vegetation, wildflowers, grasses and herbs. As Oscar Brousse, Senior Research Fellow in Urban Climatology and Health at University College London, explains, each type of roof modification has a different way of cooling cities. For cool roofs, Brousse explains, “The principle is that the energy that is coming from the sun is reflected back straight to the atmosphere and into space. So, this energy that is coming in the first place is simply not accumulated in the city, in the buildings, in the streets, etc.” Researchers including Brousse conducted a study at University College London, during which they analyzed the temperatures of different roofs and environments across the city of London on two hot summer days in 2018. The study found that while green roofs are effective in lowering temperatures during the day, they actually increase surrounding temperatures during the night—thus suggesting they are not as effective as other roof modification systems, like cool roofs. This article was provided by The Associated Press.