A family shelters in the shade of a tree at Ciutadella Park, a designated climatic refuge, part of Barcelonas Climate Shelter Network (CSN), where residents can take shelter during extreme heat, in Barcelona, Spain, on Wednesday, Aug. 3, 2022. Recent heat waves have sparked deadly wildfires in Spain, Portugal and France, adding to the challenges facing Europe from political upheaval to travel chaos and surging prices.
Covering a third of cities with trees would significantly cool the urban environment and help thousands of people survive Europe’s increasingly hot summers, according to scientists.
About one third of 6,700 premature deaths attributed to heat in 2015 — an average European summer — could have been prevented if 30% of city surfaces were planted with trees, according to a report published on Tuesday in The Lancet.
“High temperatures in urban environments are associated with negative health outcomes, such as cardiorespiratory failure, hospital admission, and premature death,” said Tamara Iungman, a researcher at the Barcelona Institute for Global Health in Spain and lead author of the report. Mitigating and adapting to heat “is becoming increasingly urgent as Europe experiences more extreme temperature fluctuations caused by climate change.”
The planet has warmed about 1.1C on average since pre-industrial times and is headed toward warming of around 3C by the end of the century as levels of greenhouse gases in the atmosphere continue to rise. But cities — most often built with heat-trapping materials like asphalt, cement, glass and steel — have it worse. The so-called urban heat island effect means European city temperatures in summer can be as much as 2C higher than in the countryside, the paper found.
The study, which is the first of its kind, modelled the impact of planting trees in 93 cities in Europe. It combined tree cover, temperatures and health and age data for 57.9 million Europeans aged over 20 between June 1 and August 31, 2015. In all the scenarios run by the scientists, increased tree coverage resulted in lower temperatures which, in turn, helped prevent deaths attributable to heat.
“Predictions based on current emissions reveal that heat-related illness and death will present a bigger burden to our health services over the next decade,” Iungman said. “Our ultimate goal is to inform local policy and decision-makers about the benefits of strategically integrating green infrastructure into urban planning.”
Only 14.9% of city areas analyzed in the study was covered by trees. But if that area doubled, temperatures would fall by a mean of 0.4C and 2,644 premature deaths due to heat would be prevented. That’s equivalent to 1.84% of all summer deaths.
An even greater increase of tree cover, to 40%, would cool the cities by 0.5C. Under that scenario, 3,727 deaths would be prevented. That suggests that the health benefits of increasing tree coverage in cities are exponential.
Overall, the cities with the highest mortality attributable to the effects of the urban heat island were in southern and eastern Europe, specifically Spain, Italy, Hungary, Croatia and Romania. Areas with the lowest mortality were mainly in northern Europe and included Sweden, Estonia, the UK and northern France.
Cities with the highest mortality are also densely populated — Paris, Thessaloniki, Athens, Bilbao or Brussels. Densely populated neighborhoods — which are usually where low-income families live, and which have the lowest tree coverage — also registered higher heat mortality rates, a conclusion that draws the link between poverty and vulnerability to climate change.
On a standardized basis, the lowest heat mortality was in Sweden’s Gothenburg, where no premature deaths were recorded. The highest was in Cluj-Napoca in Romania, where heat deaths were at 32 for every 100,000 people. The highest impact of planting trees would be in Spain’s Palma de Mallorca, where it would prevent 22 deaths for every 100,000, while the measure would have no impact in Norway’s capital Oslo.
Researchers also used satellite data to estimate the proportion of open space in each of the 93 cities where trees could potentially be planted and concluded that 30% of tree coverage is a feasible target.
To contact the author of this story:
Laura Millan Lombrana in Madrid at email@example.com
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