Cool Trees

PROBLEM: As the world warms and cities grow larger, the urban heat island effect has become an increasing threat to human health. New research published in The Lancet found that urban heat islands are responsible for 4% to as much as 33% of deaths in 93 European cities during summer months.

SOLUTION: The study determined that one-third of the deaths could be prevented if the cities achieved 30% tree cover. Researchers first estimated the mortality rates of people over 20 and studied daily temperature data for the studied cities for the summer (June–August) of 2015. This allowed them to calculate the number of premature deaths caused by the urban heat island effect. They then determined what the effect would be on temperatures and premature deaths if tree cover was increased to 30%. They found that summertime urban temperatures were 1.5°C warmer on average than in surrounding areas, and those hotter temperatures caused 6,700 premature deaths (4.3% of all summer deaths that year). They also found that increasing tree cover to 30% of all urban space could have prevented a third of those deaths. The study revealed that deaths were most impacted by extreme heat in southern and eastern Europe. According to coauthor Mark Nieuwenhuijsen of the Barcelona Institute for Global Health, the study is meant to “inform those responsible for local administrations of the advantages of integrating green areas in all neighborhoods to promote more sustainable, resilient, and healthy urban environments.” While the study underscores the importance of planting more trees in urban areas, Nieuwenhuijsen also emphasized “the need to preserve and maintain the trees we already have because they are a valuable resource and new trees take a long time to grow. Furthermore, it is not just about the number of trees, but also about how they are distributed.” [Source: Barcelona Institute for Global Health]
 

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