Urban challenges due to rising temperatures
Our cities are heating up more and more. Concrete, asphalt and sealed surfaces store heat and cause temperatures in urban areas to rise dramatically. The so-called urban heat island effect means that it is often several degrees warmer in urban centres than in the surrounding areas. This leads to heat stress for people, animals and plants, especially in the summer months.
When cities become a health hazard
The municipality of Parque Arará favela in Rio de Janeiro is one of the urban heat islands, an area without greenery that tends to suffer from extreme heat.
A 2015 study by the Federal Rural University of Rio de Janeiro showed that the temperature differences in the city are dramatic: Ground temperatures in the hottest neighbourhoods were up to 36 degrees higher than in nearby, vegetated areas. It was also found that surface temperatures in these urban heat islands have risen by 3 degrees in the last ten years.
Such extreme temperatures have a significant impact on the health of residents. Heat waves lead to severe dehydration, heat stroke and exacerbate chronic illnesses such as respiratory diseases. They can also impair cognitive functions and, in the worst case, can even be fatal.
Green roofs to protect cities and people
Green roofs have a natural cooling function based on the principle of evaporation. Plants on green roofs absorb rainwater and gradually release it back into the environment. This process of evaporative cooling ensures a noticeable reduction in temperature – both directly on the roofs and in the surrounding area. Studies show that green roofs can reduce the ambient temperature by up to 4 °C.
Green roofs also act as a natural layer of insulation. While they keep the heat inside the building in winter, they prevent excessive heating in summer. This means less energy consumption for air conditioning, which not only reduces electricity costs, but also cuts CO₂ emissions. Studies show that buildings with green roofs require up to 30 % less energy for cooling than those with conventional roofs.
Another decisive advantage is water storage. Green roofs absorb rainwater and release it again in a controlled manner. This not only prevents the sewerage system from being overloaded during heavy rainfall, but also helps to humidify the air. This additional moisture makes the urban climate more pleasant, while at the same time regulating the water balance in the long term.
