White roofs could make cities cooler
Due to climate change, cities are experiencing new temperature records, especially in urban areas. Researchers are therefore looking for ways to cool down. In simulations, the effects of various roof types in London are being tested. A particular variant stands out.
Cities are real heat islands in the summer, so cooling measures for urban areas are urgently needed. Reflective roofs could be particularly effective, according to a new study based on computer simulations. They could reduce temperatures in London on hot summer days by up to 1.2 degrees Celsius, and even up to two degrees in some neighborhoods. Green roofs, street greenery, and photovoltaic systems had a low to negligible effect.
For the study published in the journal "Geophysical Research Letters," a research group led by Oscar Brousse from University College London analyzed the effects of various measures on temperatures in the Greater London area. The scientists used data from July 26 and 27, 2018, the days with the highest temperatures ever recorded in the British capital. With a spatial resolution of one kilometer and a temporal limitation of one hour, the eleven simulation runs of the three-dimensional model provided detailed temperature developments in the various city districts.
White paint, lighter concrete or metals
Reflective roofs performed best in this regard. This concept includes various measures, such as whitewashing, the use of a special thin-film material, and the use of light concrete or metals. They all reflect sunlight to a high degree, preventing the roofs from heating up significantly.
The study found much lower effects for other approaches. If all roofs in London that could be covered with solar panels were covered, this would reduce the temperature by 0.5 degrees. More trees and other street greenery led to a decrease of 0.3 degrees. Green roofs would lower temperatures by about 0.5 degrees during the day, but raise them by the same amount at night. Plants cool their surroundings through transpiration, but this is also associated with higher humidity, which contributes to the heat.
"We have tested several methods comprehensively to help cities like London adapt to rising temperatures and mitigate them," explained Brousse. "We found that reflective roofs offer the best opportunity to keep temperatures low on extremely hot summer days. Other methods have important side effects, but none of them can reduce outdoor temperatures in the city to almost the same extent as reflective roofs." In southern countries, this effect has been used for longer by painting exterior walls and roofs white.
Researchers calculated how much energy solar cells on London rooftops could provide: It would be enough to power climate systems city-wide. However, since climate systems extract heat from buildings and release it outside, the cooling to an indoor temperature of 21 degrees would raise the average city temperature by 0.15 degrees. In densely populated central London, it would even be about one degree warmer outside.
City dwellers have a lower carbon footprint, on average
Another study considered the carbon dioxide emissions from people in cities. In fact, the inhabitants of densely populated inner cities emit less CO2 per capita than those in other areas, meaning they contribute less to global warming.
Compact, densely populated cities are considered a sustainable future model because they encourage walking and public transportation for commuting to essential facilities. Additionally, many apartments in a building require less heating per household.
An analysis of data from 919 European cities, including 127 German cities, confirmed that the inhabitants of densely populated cities have a lower carbon footprint than those of other places. The study was published by a team led by Mark Nieuwenhuijsen from the Institute for Global Health in Barcelona, Spain, in the journal "The Lancet Planetary Health".
Dense population has disadvantages
However, city dwellers also face some disadvantages. "This study shows that European compact cities, compared to cities with lower population density, tend to have poorer air quality, fewer green spaces, higher local surface temperatures, and higher mortality rates," write the study authors. They advocate for the further development of compact cities and mitigating the negative effects of dense urbanization.
Since early July, Germany has had the Climate Adaptation Act. It provides a framework for the federal government, states, and municipalities to propose strategies and measures for adaptation. For example, urban areas should be designed to capture rainwater and keep it in the water cycle. In this way, flooding, as well as heat and drought, could be counteracted.
- To combat global warming and its effects, such as heatwaves, researchers are exploring various solutions for cooling urban areas, with reflective roofs being found to be particularly effective in reducing temperatures, especially in cities like London.
- The City of the Future must consider climate change and its impact on cities, as studies show that cities, like London, are experiencing new temperature records due to global warming. This highlights the need for innovative solutions like reflective roofs to mitigate the rise in temperatures.
- As global warming continues to cause heatwaves and temperature increases in cities, it's crucial to invest in cooling measures like reflective roofs. These can significantly reduce urban heat islands, as shown in simulation studies conducted on London, contributing to a more comfortable and sustainable City of the Future.
