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[Michaelangelica]

17/9/07

- 'Green roofs' could cool warming cities

NewScientist.com news service -Catherine Brahic

Covering city buildings in vegetation – creating “green roofs” and walls – could substantially save energy by reducing the need for air conditioning on hot days, say researchers.

Green roofs and walls can cool local temperatures by between 3.6°C and 11.3°C, depending on the city, suggests their new study.

Eleftheria Alexandri and Phil Jones at the Welsh School of Architecture, at the University of Cardiff in the UK, mimicked the microclimate around and inside buildings using computer modelling. They compared local temperatures when buildings were made of bare concrete with when the concrete was covered in vegetation.

Such green surfaces are already in use – roofs that are strong enough to take the additional load can be covered with mosses, turf and even trees. In Switzerland, roofs covered in alpine plants that require little soil are becoming increasingly common. Walls can also be greened, often by climbing plants planted at ground level.

Temperature drop

The researchers compared the effects of green surfaces in nine cities around the world, including subarctic Montreal in Canada, temperate London in the UK, humid Mumbai (India), and tropical Brasília (Brazil). In all cases, they studied the month during which that city sees its hottest temperatures.

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