In Paris, trees reduce mortality linked to heat waves

In Paris, districts with more vegetation have a lower risk of mortality during periods of high heat, while highly built areas with few green spaces and a high potential for urban heat islands are the most exposed. This is the finding of an international study conducted by Inserm, the Barcelona Institute for Global Health (ISGlobal), a centre supported by the ”la Caixa” Foundation, and the London School of Hygiene & Tropical Medicine, published in the journal npj Urban Sustainability, based on data collected over nearly ten years, from 2008 to 2017. The scientists emphasize the importance of developing vegetation in cities and better distributing green spaces among neighborhoods to protect the health of Parisians in the face of global warming.

Due to the urban heat island effect, Paris is particularly vulnerable to heat waves, which are expected to intensify as a result of climate change caused by human activity. The capital is even among the European cities with the highest risk of heat-related excess mortality: when temperatures are above normal, mortality increases by a factor of 1.6 among people over 85, according to a study published in The Lancet in 2023.

In order to better understand the risk factors and identify solutions to make the city more resilient, a research team compiled data on heat-related excess mortality, district by district, cross-referencing it with the characteristics of the built environment and the urban environment (vegetation, heat islands) as well as socio-economic indicators. The study, published on January 27 in the journal npj Urban Sustainability, is based on data collected over nearly ten years, from 2008 to 2017.

The protective effect of green spaces

It confirms an initial finding, already well documented in scientific literature: green spaces have a protective effect against heat-related excess mortality. The presence of trees, parks, gardens, or green roofs is associated with lower temperatures in the capital.

But not all green spaces offer the same protection. Scientists point out that trees are significantly more effective than lawns at reducing the risk of death during heat waves, thanks to the shade they provide and evapotranspiration.

In addition, scientists have observed that the cooling effect of vegetation only partially explains its protective effect on the health of Parisians: “Although the exact mechanisms still need to be explored, key factors such as reduced pollution and improved physical and mental health could play a decisive role,” explains Hicham Achebak, a researcher at Inserm and ISGlobal and lead author of the study.

Inequalities beyond socioeconomic status

Above all, the study reveals significant inequalities within the capital. More than the socioeconomic status of residents, it is mainly the age and characteristics of buildings (those built before the 1970s being less well insulated), as well as the presence of green spaces, which varies from 1.4% in the 2nd arrondissement to 20.4% in the 13th, that determine the risk of higher mortality during periods of high heat.

The greenest districts are those where the risk of heat-related deaths is lowest. Conversely, the most built areas, with few green spaces, are more vulnerable. “This statistical reality highlights a clear divide between the center of the capital, which is more subject to the urban heat island effect, and the outlying districts, which are better protected by their green spaces,” the researcher points out.

The study also highlights a counterintuitive finding: “Contrary to popular belief, the wealthiest districts of Paris are, on average, more vulnerable to excess mortality linked to high temperatures. This phenomenon can be explained by the lack of green spaces, combined with dense, mineral-based old buildings in these neighborhoods,” explains Hicham Achebak.

Potential to prevent up to one third of mortality

Using models, the scientists then attempted to assess how many deaths could be prevented by continuing to develop green spaces in the capital. "The greenest districts of Paris currently have around one-fifth of their area covered by vegetation. According to our calculations, if all districts reached this level, heat-related mortality could be reduced by about a third, both during periods of moderate heat (temperatures above 22°C) and during the most intense heat waves (above 25°F), explains Grégoire Rey, former director of Inserm's Center for Epidemiology of Causes of Death (CépiDc) and last author of the study. These estimates are based on modeling and should be interpreted with caution, but they reflect the essential protective role of vegetation that we observe."

Beyond efforts to green the capital, scientists have identified several additional measures to help Paris adapt to high temperatures: the use of reflective materials for roofs and pavements, improving the energy efficiency of buildings to limit heat emissions (particularly from air conditioning), and reducing car traffic, which would decrease both residual heat and air pollution.

“These results highlight the importance of developing vegetation in the city and distributing green spaces more evenly across neighborhoods. Strengthening the place of nature in urban areas thus appears to be a major lever for protecting the health of Parisians in the face of global warming,” concludes Hicham Achebak.

Reference
Hicham Achebak, Pierre Masselot, Joan Ballester, Antonio Gasparrini & Grégoire Rey Greening mitigates heat-related mortality in Paris. npj Urban Sustain (2026). https://doi.org/10.1038/s42949-025-00334-5