- Urban heat islands are becoming a major source of concern.
- There are technical solutions, but in the long run cities should be designed differently.
Streets swelter, entire neighbourhoods are transformed into baking ovens, and residents are left exhausted by stifling heat. “Higher temperatures in cities are an increasingly noticeable issue, particularly at night,” says Thomas Auer, an expert on sustainable construction at the Technical University of Munich (TUM). “The heat produced by the sun, traffic and air-conditioning systems is absorbed by the tarmac and the walls of buildings during the day, and is then released at night.” Worsened by dark building exteriors and a lack of green spaces, which promote cooling, the formation of urban heat islands (UHIs) is becoming an issue of concern, especially with global warming set to further exacerbate this phenomenon. During the heatwave of 2003, which was responsible for the premature deaths of 70,000 people in Europe, the temperature difference between major European cities and rural areas exceeded 8° C.
What can be done to alleviate this? “Reflective construction materials can minimise UHIs,” says Auer. Other researchers, like TUM’s Philipp Molter, are testing “skins” designed for use in the building envelope. In his laboratory, he and his team are working on the Flexcover project, which has created self-regulating windows modelled on human skin. Just like the skin’s pores, which can open and close in response to the temperature, they form an envelope that can “breathe”, adapting the building’s temperature to the conditions outside.
Rethinking urban design
Even so, the real response won’t be found at the building level or even at the neighbourhood level, says Auer. Our whole approach to urban design needs a rethink, particularly when it comes to new districts. “Reducing urban density isn’t necessarily useful. However, we need to create a roadmap that we can use to adapt cities to the climate, to promote wind circulation in new urban areas using specially-designed corridors, like in Hong Kong, or to increase the surface area devoted to green spaces while ensuring these spaces are distributed across the city.” The transformation will take decades, but a number of major cities have already started. New York, for example, has painted the roofs of around 100 buildings white to reduce the amount of energy consumed. Since then, airconditioning bills have fallen by 10% for five-storey buildings. What’s more, while Helsinki and Copenhagen are leading the way in Europe, Paris has been looking into urban renovation for around a decade, and Moscow has plans to redesign 3,000 major roads as part of My Street, a huge urban renovation project begun in 2015.