Urban Heat Island Effect
The concentration of buildings and paved areas in cites leads to the formation of a specific urban climate, characterised in particular by higher night-time temperatures, increased humidity and polluted air or even smog because of the restriction of airflows.
Green roofs and green spaces help with the overall cooling effect as evapotranspiration takes place from the plants and the amount of heat radiated from dark and hard surfaces is reduced. Measurements and modelling of green roofs suggest they can:
- Reduce summer roof surface temperatures by between 10 and 30 degrees centigrade
- Reduce the urban heat island effect by up to 2 degrees centigrade.
The larger the green areas in a city the greater the temperature modifying effect. This is increased if the roofs are irrigated thus ensuring transpiration is as effective as possible.