Exposure to vegetation has numerous health benefits. Many studies have shown that people living in areas with more vegetation enjoy better mental, cardiovascular, and perinatal health. As a result, the WHO’s French Healthy Cities Network considers urban green spaces to be a tool for promoting health and equity.

The mechanisms through which vegetation affects health are not yet fully understood. Three primary pathways of action have been identified:

1. Reducing exposure to environmental stressors: air pollution, heat, noise, etc.

2. Contributing to capacity building by facilitating physical activity, social interaction, etc.

3. Restoring well-being through psychological recovery and stress reduction.

In line with the “One Health” approach, a fourth focus can be added: the protection of biodiversity.

Vegetation’s ability to reduce heat through shading and evapotranspiration makes it a central tool in climate change adaptation policies.

The effects of heat, air pollution, and vegetation on health are often studied independently. However, the existing interconnection between heat, vegetation, and air pollution raises the question of potential synergistic effects on health that remain poorly understood and under-researched.

A first step in studying these combined effects is the cross-analysis of these three exposures at a fine scale, over a long period of time, and across the entire national territory—something that had not been done until now. To do this, we created relative indicators that are comparable across all regions. This allows us to account for the diversity of climates and vegetation in France and to overcome the difficulty of using absolute temperature or NDVI (a satellite index measuring chlorophyll activity) values, which are difficult to compare across regions.

Defining these exposures has allowed us to identify environmental hotspots—areas with the highest cumulative overexposure to heat, air pollution, and lack of vegetation—and to study their association with social disadvantage.

This study highlights a higher level of heat exposure during the 2015–2018 period compared to the 2000–2014 period, which is consistent with the climate trends observed in France. Regarding ambient air pollution, although air quality improved between 2000 and 2018 for most pollutants, most of the urban areas studied remained above the WHO’s 2021 air quality guideline values in 2018. For example, 99.9% of urban areas had fine particulate matter (PM2.5) concentrations exceeding the guideline values. On average, 7% of the areas studied had the highest cumulative overexposure levels for the three factors examined (environmental hotspots). This percentage was similar in both rural and urban areas.

Finally, the most disadvantaged urban areas were at higher risk of being environmental hotspots. These results are not observed in rural areas, which can likely be explained by a more heterogeneous distribution of disadvantage and less granular spatial scales than in urban areas.

Source: J Expo Sci Environ Epidemiol - Design: Lucie Adelaïde

By examining the combined effects of heat exposure, lack of vegetation, and air pollution at the national level and in relation to social disadvantage, our findings align with the strategies outlined in the 2nd Climate Change Adaptation Plan and the 4th National Environmental Health Plan for addressing and integrating social inequalities into environmental health initiatives. This study encourages local stakeholders to address the issue of environmental justice in their adaptation policies by providing them with tools for inter-territorial comparisons at a fine spatial scale. This could, for example, enable the prioritization of certain territories experiencing higher cumulative exposures and greater social disadvantage, while taking into account local specificities and contexts.

With the upcoming release of data on data.gouv.fr, the environmental exposure indicators developed as part of this study will also be usable to examine the combined effects of temperature, air pollution, and vegetation on health, in relation to social inequalities. For example, we are studying the effects of heat, co-exposures (air pollution, vegetation), and social status on perinatal health, a major public health issue.

It is also important to note that the overseas departments and regions (DROM) could not be included in this study because the necessary data were not available, even though these territories are particularly vulnerable to climate change. Work is underway to assess the relevance and feasibility (availability and access to environmental data, etc.) of extending this study to the DROM.

This research addresses the need to develop knowledge for the implementation of equitable and just climate change adaptation.