Washington: We all know that greenery is important to combat global warming, but researchers have found that just more green space cannot help to lower temperature everywhere. Urban heat islands are a phenomenon where the temperature in a city is noticeably higher than in the surrounding rural area. When combined with the sort of heatwave that hit many parts of Europe at the beginning of July, urban heat can pose a real threat to the elderly, sick or other vulnerable people.
“We already know that plants create a more pleasant environment in a city, but we wanted to quantify how many green spaces are actually needed to produce a significant cooling effect,” said Gabriele Manoli, former postdoc with the Chair of Hydrology and Water Resources Management at ETH Zurich
The urban heat island phenomenon is more pronounced the bigger the city and the more rainfall in that region. This effect is the strongest when annual rainfall averages around 1500-millimetre as in Tokyo but does not increase further with more rain. Through carefully targeted planting, a city like Phoenix in the USA could achieve cooler temperatures than the surrounding countryside, where conditions are almost desert-like.By comparison, a city surrounded by tropical forests such as Singapore would need far more green spaces to reduce temperatures, but this would also create more humidity.
