According to a new study led by the Barcelona Institute for Global Health (ISGlobal), over four percent of deaths in cities during the summer months are caused by the formation of “urban heat islands,” where cities experience higher temperatures than surrounding areas due to less vegetation, larger population density, and the presence of impermeable surfaces for buildings and roads, including asphalt. By analyzing data from 93 European cities (with a total of 57 million inhabitants), the experts determined that one third of these deaths could be prevented by reaching a tree cover of 30 percent.
Exposure to extreme heat has been associated with cardiorespiratory diseases, a higher number of hospital admissions, and premature deaths. While these problems are mainly caused by heatwaves, they also occur with moderately high temperatures in the summer. Due to the formation of urban heat islands, cities are especially vulnerable to higher temperatures, facing spikes in morbidity and mortality during summer worldwide.
“Predictions based on current emissions reveal that heat-related illness and death will become a bigger burden to our health services over the next decades,” warned study lead author Tamara Iungman, a biologist at ISGlobal.
The scientists found that, from June to August 2015, cities were on average 1.5C warmer than the surrounding countryside, a phenomenon leading to 6,700 premature deaths in the 93 cities that were examined (4.3 percent of total mortality during the summer months and 1.8 percent of year-round mortality). Cities with the highest excess heat-mortality rates were in Eastern and Southern Europe. However, projections revealed that one third of these deaths (2,644) could have been prevented by increasing tree cover by 30 percent.
These findings highlight the major benefit of planting more trees in cities, together with other interventions such as green roofs.
“Our results also show the need to preserve and maintain the trees that we already have because they are a valuable resource and it takes a long time to grow new trees. It is not only about increasing trees in the city, it is also about how they are distributed,” added study senior author Mark Nieuwenhuijsen, the director of the Urban Planning, Environment and Health Initiative at ISGlobal.
“Vulnerability to heat changes from city to city depending on several factors. Understanding the benefits of policies such as increasing tree cover can help inform action to reduce risks and prevent avoidable deaths, especially with climate change,” concluded co-author Antonio Gasparrini, a professor of Biostatistics and Epidemiology at the London School of Hygiene & Tropical Medicine (LSHTM).
The study is published in the journal The Lancet.
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