Environment: A 5% increase in urban trees could prevent 5,000 deaths per year

An increase in tree cover in cities of 5% would reduce air pollution ^[1] enough to prevent around 5,000 premature deaths each year. This is the result of an international study involving ENEA and conducted in 744 cities across 36 European countries. The findings were published in The Lancet Planetary Health and carried out as part of the EU LIFE “Airfresh” project. The research also shows that up to 12,000 deaths per year could be avoided if every city achieved a tree canopy cover of at least 30%.

“In urban areas, fine particulate matter, nitrogen dioxide and ozone are among the most harmful pollutants for both human health and ecosystems. By 2050, it is estimated that around 80% of the European population will live in urban environments, which will further increase the significance of these issues,” explains Alessandra De Marco, ENEA project coordinator and head of the Laboratory for impacts on territories and developing countries. “Increasing the number of trees in cities,” she adds, “would offer simultaneous benefits such as improved air quality, mitigation of the urban heat-island effect, biodiversity conservation and, above all, enhanced well-being for citizens.”

The United Nations Economic Commission for Europe (UNECE) recommends adopting the 3-30-300 rule, which aims to achieve three specific goals: 3 trees visible from every home, school or workplace; 30% tree canopy cover in every neighborhood; and a maximum distance of 300 meters between residences and a park or public green space.

The study used an integrated approach combining environmental and health data at the European level ^[2]over a 20-year period (2000–2019). It shows that average tree cover increased by only 0.76 percentage points, with 73.5% of analysed cities experiencing some degree of greening. At the same time, mortality attributable to air pollution decreased by an average of 3.4%. In 2019, 130 of the 744 urban centres examined (representing over 50 million inhabitants - around 25% of these cities' populations) had an average tree canopy cover of over 30%. Currently, tree cover in Italy reaches 30% only in Naples (32%), while in Milan and Rome it stands at just 9% and 24%, respectively.

Achieving 30% urban tree cover — similar to what some European cities have already reached — could reduce premature deaths by 9.4% from PM2.5 exposure, 7.2% from nitrogen dioxide and 12.1% from ozone. By contrast, reducing tree cover to zero would lead to increased mortality: +19.5% from PM2.5 (around 19,000 additional premature deaths per year), +15% from nitrogen dioxide (over 5,200 more) and +22.7% from ozone (around 700 more)', notes De Marco. The benefits of urban greening extend beyond improving air quality. Trees can also reduce perceived temperatures, helping to mitigate the impact of heatwaves such as the one experienced in summer 2022, which caused around 62,000 additional deaths in Europe (+4%).

The EU Biodiversity Strategy for 2030 commits Member States to planting at least 3 billion trees by the end of the decade, to significantly increase average tree cover in cities. “To achieve this goal, planting programs should involve not only public spaces but also—indeed, especially—private areas such as residential courtyards, as well as peri-urban zones. It is essential that urban planners and local administrators be encouraged to integrate green infrastructure tailored to the specific characteristics of each area. This approach should be coupled with emission-reduction policies and complementary interventions, such as cool-air corridors or green roofs, to maximize benefits for public health and quality of life, ultimately leading to more sustainable and climate-resilient cities in the long term,” De Marco concludes.