Euronews Green of AP writes:

Green roofs bring great biodiversity benefits, but have one key drawback as a cooling solution according to a new study. A bird’s eye view of London is increasingly appealing, with more and more rooftops turning green or white across the capital. Green roofs involve planting vegetation up top, while the latter is essentially a paint job. Both designs are intended to lower urban temperatures and keep people cool, but how do they work exactly - and which is more effective?

How do green roofs keep cities cool?

11 stories high, the green roof on top of investment bank Nomura’s European headquarters in Moorgate, central London, is exemplary. It 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. The purpose of green roofs like this one is to help lower the air temperature.

Under the ‘urban heat island’ effect, temperatures can often be 10 degrees hotter in cities than rural areas as tall buildings trap heat and materials like asphalt and concrete absorb it. As public health expert Mathilde Pascal told Euronews Green in a recent interview, 10 degrees is “the difference between something you can adapt to and something that is completely overwhelming.”

Plants help alleviate this effect as they store heat, which is then released when they transpire.

Read more: Rare orchids and bees are thriving on London’s green rooftops as city eyes up cooling solutions