2024-04-21 17:18:32
As climate change accelerates across the planet, a growing number of studies suggest that exposure to heat, combined with exposure to other environmental factors, such as air pollution or The absence of vegetation can increase health vulnerabilities.
This is all the more true as the most exposed populations are often also the most disadvantaged. To best protect health therefore requires a better understanding of the interactions between environmental exposures and social disadvantage.
Based on this observation, we carefully characterized exposure to heat, air pollution and lack of vegetation in mainland France between 2000 and 2018. This work, carried out in collaboration between Public Health France and Inserm, allowed us to define “environmental black spots” and describe their evolution in time and space, while exploring their associations with social vulnerability.
The most disadvantaged populations are also the most exposed
In recent years, studies conducted in Europe and the United States have revealed that geographic areas with cumulative exposure to multiple environmental stressors are also often those in which the most socio-economically disadvantaged populations reside.
These already vulnerable residents may therefore be more exposed to heat, air pollution, or have less green space.
However, it is also now known that the accumulation of several of these environmental exposures can have synergistic effects on health. For example, exposure to heat and ambient air pollution increases the risk of cardiovascular and respiratory diseases.
Conversely, vegetation not only plays a protective role once morest heat and ambient air pollution, but it also has many positive effects on health, for example improving mental health or cognitive functions. This is particularly due to the fact that green spaces help reduce stress, improve social cohesion and encourage physical activity.
In cities, like here in Bordeaux, green spaces have many virtues. Shutterstock/David Fadul
However, despite a very abundant scientific literature, certain questions remained unanswered until now. Thus, no study had taken into account the accumulation of three exposures (to heat, to air pollution, to lack of vegetation), which are nevertheless very interdependent due to shared physicochemical processes. For example, certain weather conditions (hot, sunny days) can be favorable to increasing concentrations of certain air pollutants. The presence of vegetation in the city allows the temperature to be reduced (shade, evapotranspiration).
In addition, numerous studies have been carried out at the local scale, over relatively short periods (one or two years), but none had been carried out, in a very precise manner, on the scale of France and over a long time.
This new work draws the spatio-temporal trends in exposure to heat, air pollution and lack of vegetation in mainland France between 2000 and 2018 and makes it possible to define “environmental black spots”, while exploring the associations possible with indicators of social disadvantage.
Determination of “environmental black spots”
Environmental black spots are understood here as areas of accumulation where populations are potentially exposed to multiple environmental nuisances: exposure to heat, air pollution and the absence of vegetation.
In order to carry out this study, we looked at 48,185 French census districts (inframunicipal scale of IRIS – Ilots Regroupeés pour l’Information Statistique). We have compiled and analyzed, for the period 2000-2018, several types of data: European and French indices of social disadvantage (respectively EDI and FDep), daily ambient temperatures, concentrations of particles (PM2.5 and PM10), carbon dioxide nitrogen and ozone, and vegetation index.
Reference values were chosen to characterize (over)exposure in relation to the World Health Organization thresholds for air pollution, and to climatic and regional averages for temperature and vegetation.
Aerial view of the city of Paris. Shutterstock/Alfonso de Tomas
The two indices of social disadvantage take into account different parameters (the EDI provides information in particular on the level of education, unemployment, household overcrowding, single parenthood, car ownership, while the Fdep provides information on median income, as well as the share of baccalaureate holders, workers and unemployed). However, both have in common that they rely on data from censuses to estimate the socio-economic characteristics of districts. The vegetation index reflects the density and vigor of the vegetation.
We compared environmental exposures over the period 2000-2014 with those of the period 2015-2018. Furthermore, the associations between “environmental black spots” and social disadvantage were then evaluated by statistical analyses.
More than 4 million French people affected
The results obtained indicate that on average, more than 4 million people lived in “environmental black spots”, in other words areas with the greatest overexposure to heat, air pollution and lack of vegetation.
One of the central points of our work is the demonstration that significant social disadvantage is strongly associated, in urban areas, with the risk of living in an “environmental black spot”. However, this association is not found in rural areas.
In other words, when living in a city, being socially disadvantaged predisposes you to living in places that have the highest environmental exposures.
Our results also indicate that the period from 2015 to 2018 was much warmer than the period from 2000 to 2014, confirming other work which already reported this phenomenon.
They also reveal important differences between rural and urban areas. Thus, between 2000 and 2018, urban districts were generally more exposed to summer heat and air pollution than rural districts, while having less vegetation.
Concentrations of pollutants in the air decreased during this period, but they still remained higher, in 2018, than the thresholds recommended by the World Health Organization.
A tool for scientists as well as stakeholders
These results constitute a valuable resource for all research teams working on climate policies and/or environmental health.
The environmental exposure indicators constructed as part of this study will be made available on the data.gouv.fr website and can be used by those who wish to do so in new work on the effects of temperature, pollution of air and vegetation on health and social health inequalities.
In our future work, we will use these indicators to assess the cumulative effects of heat, air pollution and the absence of vegetation, on the health of the newborn, also taking into account social characteristics.
But this study is not only useful to scientists: all stakeholders, particularly political decision-makers, can use it. These inter-territory comparison tools, on a fine spatial scale and over a long period of time, can provide food for thought for the implementation of urban development and adaptation to climate change measures. They constitute an additional opportunity to address the question of environmental justice, which is also a question of social equality and public health…
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