Painting roofs white can reflect sun's heat and prevent deaths in cities during heatwaves
Thousands of lives lost each year in heatwaves could be prevented by painting roofs white, new research suggests.
Cities can heat up by an extra 9°C compared to surrounding areas - an effect called the 'urban heat island'. But painting roofs in colours that reflect heat back into space can keep buildings significantly cooler.
Around half of deaths during heatwaves - mainly the elderly - are thought to be caused by the extra heat in cities.
Experts calculate how many people die during heatwaves, compared to how many would die normally.
The Oxford University study said the 'heat island' effect is caused partly by a lack of moisture and vegetation in cities compared with rural landscapes, and because urban building materials store up heat.
The study, published in Environment International, suggested that implementing cool roofs across the city can reduce peak daytime local temperatures by up to 3c during a heatwave.
To achieve this reduction would require around half of the commercial and industrial buildings in the city to paint their roofs.
This reduction in temperature could potentially offset around 25 per cent of the heat-related mortality associated with the urban heat island during a heatwave.
Applied worldwide it would lead to reductions of thousands of deaths, the research suggests.
The urban heat island effect is most pronounced at night time, because urban materials release their stored heat overnight, however, the biggest benefits of cool roofs were seen to be during the hottest part of the day where sunlight was reflected away.