More green spaces in cities could significantly reduce premature deaths and their costs, researchers say.
Focusing on Philadelphia, they concluded that increasing the city's tree canopy by about one-third – from 20% to 30% of land area – could prevent more than 400 premature deaths a year and save nearly $4 billion in related economic costs.
Increases of 5% and 10% in tree canopy could prevent premature deaths a year by 271 and 376, respectively, according to the study led by the Barcelona Institute for Global Health (ISGlobal) in Spain and the US Forest Service.
Poorer neighbourhoods would see the greatest benefits from an increase in green spaces.
"Many of the deaths prevented would be in the poorest areas of the city, even with a moderate increase in the number of trees," said study first author Michelle Kondo, a research social scientist at the US Forest Service.
Researchers noted that Philadelphia is the poorest of the 10 largest US cities and its death rate is higher than the national average.
"Urban reforestation programmes are not only essential for improving public health, they are also a way to reduce health inequities and promote environmental justice," Kondo said in an ISGlobal news release.
Kondo noted that large tree-planting initiatives face many obstacles, including losses from tree pests and invasive species, as well as urban development.
Study coordinator Mark Nieuwenhuijsen said the study has lessons for cities worldwide.
"Although every city has its own characteristics, this study provides an example for all the cities in the world: Many lives can be saved by increasing trees and greening urban environments, even at modest levels," he said in the release. Nieuwenhuijsen is director of ISGlobal's Urban Planning, Environment and Health Initiative.
"What's more, green spaces increase biodiversity and reduce the impact of climate change, making our cities more sustainable and more livable," he added.
The findings were published in the April issue of the The Lancet Planetary Health journal.