From parks to sports fields, green spaces are an essential component of urban ecosystems. They are a refuge from the noise of the city, they filter harmful pollution, provide routes for walking, and even prevent many premature deaths per year, according to a new study.

US and Spanish researchers concluded that by increasing tree coverage to 30% of the land area in Philadelphia, United States, over 400 premature deaths could be prevented every year — leaving the city with an economic benefit of $4 billion.

“Achieving this goal does not come without challenges. Large tree planting initiatives are faced with many problems, including losses from climate change, tree pests and invasive species, and urban development”, explained Michelle Kondo, first author of the study, in a statement.

The team led by members of the US Forest Service and the Barcelona Institute for Global Health carried out a health impact assessment, estimating the number of all-cause deaths that could be prevented if green spaces in a whole city were increased.

Three scenarios were identified for the city of Philadelphia for 2025. The most ambitious was based on the current goal as set by the City Council for an increase in tree coverage to 30% of land area in each of the city’s neighborhoods. The current coverage is 20% for the city as a whole.

The researchers obtained data of the existing canopy from aerial and satellite images, which allowed them to measure tree coverage. They concluded that the 30% target for the city would prevent 403 premature deaths, highlighting that even lower increases in the canopy would also bring benefits.

“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,” said Mark Nieuwenhuijsen, the study coordinator.

The study also showed that neighborhoods with a low socioeconomic level would benefit most from any increase in green spaces. Many of the deaths prevented would be in the poorest areas of Philadelphia, even with a moderate increase in the number of trees.

Previous research has shown that green spaces in urban settings are associated with benefits for the physical and mental health of the city’s residents. A recent review showed that residential green spaces can protect against premature all-cause mortality.

According to the World Health Organisation (WHO), every city is recommended to provide a minimum of 9 square meters of urban green space for each person, that it should be accessible, safe, and functional. The WHO also suggests that an ideal amount of urban green space can be generously provided as much as 50 square meters per person.

The study was published in the journal The Lancet Planetary Health.