Over 4% of deaths in European cities during the summer months are due to urban heat islands and one third of these deaths could be avoided by reaching a tree cover of 30%. This is explained by a study published in ‘The Lancet’ and conducted by the Barcelona Institute for Global Health (ISGlobal), supported by the ‘la Caixa’ Foundation. Research findings highlight the substantial benefits of planting more trees in cities to mitigate the impact of climate change. “Predictions based on current emissions indicate that heat-related illnesses and deaths will become a major burden on our health services in the coming decades,” says Tamara Iungman, ISGlobal researcher and first author of the study.
An international team led by Mark Nieuwenhuijsen, director of the Urban Planning, Environment and Health Initiative at ISGlobal, estimated the death rates of residents over the age of 20 in 93 European cities (for a total of 57 million inhabitants), between June and August 2015, and collected data on daily rural and urban temperatures for each city. The analyzes were performed at high resolution (areas of 250 meters x 250 meters). First, they estimated premature mortality by simulating a hypothetical scenario with no urban heat island. Second, they estimated the temperature reduction that would be achieved by increasing tree cover to 30% and the associated mortality that could be avoided.
“Our goal is to inform local decision-makers about the benefits of integrating green areas into all neighborhoods, in order to promote more sustainable, resilient and healthy urban environments,” explains Nieuwenhuijsen.
The results show that, from June to August 2015, cities were on average 1.5°C warmer than the surrounding countryside. In total, 6,700 premature deaths could be attributed to warmer urban temperatures, which represents 4.3% of total mortality during the summer months and 1.8% of mortality throughout the year. A third of these deaths (2,644) could have been avoided by increasing tree cover by up to 30%, thereby reducing temperatures. Overall, the cities with the highest heat mortality rates, and therefore those that would benefit most from an increase in tree cover, are those in southern and eastern Europe.
The study highlights the substantial benefits of planting more trees in cities, although the authors acknowledge that this can be difficult in some cities due to their design and that tree planting should be combined with other interventions such as green roofs or other reduce the temperature.
“Our results also show the need to preserve and maintain existing trees, because they are a precious resource and growing new trees takes a long time. It is not just about increasing trees in the city, but also understanding how they are distributed “, emphasizes Nieuwenhuijsen.
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