Heat waves are becoming more frequent and the urban design of large cities, with their lack of green areas, aggravates the intensity of these periods of extreme heat, especially for the most vulnerable population. A study led by the University of Surrey shows the best way to cool the air in urban centers: include more green spaces. This research carried out in the United Kingdom shows that the presence of botanical gardens, parks, wetlands and 'green walls' have the potential to effectively reduce air temperatures in summer, up to 5 degrees during a heat wave.
The effects of the climate crisis are increasingly evident: temperatures are rising around the world. The year 2023 has been the hottest ever recorded, and the forecast is that they will increase even more during 2024, according to the World Meteorological Organization (WMO). Heat waves are lengthening and have tripled in recent years. In addition, they are increasingly hitting new victims: more than 11,000 people died in Spain and 61,000 throughout Europe due to the heat in the summer of 2022. Faced with this growing problem, the solution must involve returning nature to urban areas.
The results of this study confirm what can already be intuited: on very hot days, we notice a large change in temperature. Green spaces are often the only outdoor refuge from the stifling climate of city streets and concrete blocks. “We have known for some time that green spaces and water can cool cities,” says Professor Prashant Kumar, director of the Global Center for Clean Air Research at the University of Surrey, as well as a professor and professor. “This study provides us with the most complete picture yet; “We can explain why: from the trees that provide shade to the evaporation of water that cools the air.”
After examining more than 27,000 research articles on green, blue and gray urban infrastructure (such as parks, wetlands and other green areas) with the potential to reduce air temperatures in urban areas, the research authors selected 202 of these for a meta-analysis. which classifies them to conclude their effectiveness in reducing temperatures in the city.
The University of Surrey study has found that botanical gardens are the most effective, and have the potential to reduce city center air temperatures by up to 5°C. Wetlands and rain gardens are the second and third most efficient ways to cool the environment, with a variation of 4.7 and 4.5°C respectively, followed by 'green walls'. According to the data, the trees planted along the streets managed to reduce the air temperature by 3.8°C and the parks managed to lower it by 3.2°C.
But how do these green areas achieve such a significant drop in urban temperature? Researchers explain that trees and plants help reduce heat by reducing the amount of direct sunlight that reaches the ground, while releasing moisture into the air. Water cools the surrounding environment through “evapotranspiration, shading, albedo effect, groundwater recharge, and temperature buffering.”
One of the best classified methods in this research are the so-called 'green walls'. According to the authors of the study, these green walls not only help insulate buildings, but also reduce heat absorption, in addition to the vegetation can serve as windbreaks for natural ventilation.
The study also remembers when on July 19, 2022 the air temperature reached 40.3°C, breaking records in the United Kingdom. That year there were 62,862 summer heat-related deaths across Europe. The researchers also recall the economic losses valued at billions of euros due to drought and poor harvests during the heat wave of 2003. Finally, they recall that the IPCC (the Intergovernmental Panel on Climate Change) considers that “Green and blue elements of urban infrastructure are particularly effective in reducing air temperatures in cities.”
The research concludes that any type of infrastructure or green area provides cooling benefits and that it is necessary to return nature to cities in densification and expansion. However, researchers recognize that there is no simple solution that fits all locations and that there must be planning to ensure long-term effectiveness specific to each location.
“Our paper confirms how many ways there are to stay cool,” adds Professor María de Fátima Andrade, from the Department of Atmospheric Sciences at the University of Sao Paulo, Brazil, “but it also reveals how much work remains to be done; “Institutions around the world need to invest in the right research, because what is very clear from our study is that there is no one-size-fits-all solution.”
