Since 2004, France has been monitoring the meteorological characteristics of heat waves and their impacts, particularly on overall mortality, as part of the interministerial directive on the public health management of heat waves in metropolitan France (formerly known as the “National Heat Wave Plan”). We have also conducted a retrospective analysis of heat waves dating back to the 1970s. This historical dataset has allowed us to identify rapid changes in the characteristics of heat waves since 2015, which directly impact prevention and warning needs. In particular, heat waves are occurring earlier (early June) and later (early September) in the season, with exposure occurring in schools or at work. All departments now experience heat waves, with some enduring multiple episodes in a single summer, which can lead to the phenomenon becoming commonplace and a relaxation in the adoption of preventive measures. For example, 65% of departmental heat waves during the 2003–2019 period occurred after 2015. Finally, while no event at the national level can be compared to 2003 in terms of geographic extent and duration, temperatures exceeding those observed in 2003 are being recorded with increasing regularity in certain departments over short periods. This led to the issuance of Météo France’s highest weather alert level, the red alert, for the first time in 2019, and again in 2020.

These trends are resulting in a greater impact on public health. Since the plan was implemented in 2004, more than 8,000 excess deaths have been recorded during heat waves, including 5,700 between 2015 and 2019.

All of this data is available on Geodes (heatwave determinants), and Santé publique France now produces a heat exposure indicator for the National Observatory on the Effects of Global Warming.

In this article, we wanted to highlight how the heat wave and health alert system works on a day-to-day basis.

Heat wave alerts are highly specific, as they rely on environmental forecasts provided by Météo-France to anticipate and prevent health impacts. This prevention requires the mobilization of numerous on-the-ground stakeholders, who must be persuaded to take action before the heat wave arrives and its effects become observable. This requires close collaboration, with daily exchanges, between Météo-France, Santé publique France, and the General Directorate of Health at the national level, and, at the regional level, between the regional units of Santé publique France located throughout the country and the regional health agencies.

During the summer, monitoring alerts, health surveillance, and prevention involve numerous departments and functions within Santé publique France: environmental health, occupational health, prevention and health promotion, alert monitoring, communication, and information systems.
The regional units play a key role in analyzing health data at the local level and relaying messages to the ARS. After each summer, national and regional reports on health impacts are published on our website. The feedback gathered each year leads to regular adjustments to the system. Some examples: extending the monitoring period through September 15 (year), modifying the criteria for red alerts (year), and semi-automating health data analysis (year).

The social marketing strategy also evolves regularly, gradually reaching all groups vulnerable to heat in addition to the general population, notably by varying communication formats (TV, radio, digital, posters, etc.). New communication tools were developed for the summer of 2021 with one main objective: to raise awareness that everyone is affected by heat waves and their potential consequences.

In 2020, it was also necessary to take the COVID-19 pandemic into account in risk analyses and health surveillance, and to verify that recommendations for protecting against heat were compatible with COVID-19 management measures.

Significant excess mortality was observed during the 2020 heat waves, particularly in northern France (under a red alert), and among people aged 45 and older. Vulnerability to heat may have been exacerbated by the pandemic context1.

The increase in the frequency and intensity of heat waves in Europe is one of the most striking examples of the already observable effects of climate change, as documented by the IPCC (Intergovernmental Panel on Climate Change) and Météo-France. Furthermore, climate scientists now have tools to determine whether a given heat wave is attributable to climate change or not.² They show that the heat waves observed since 2015 would have been less intense without this warming (for example, 1.5 to 3°C less intense in 2019), or even impossible without it (for example, the late episodes of 2016).

In addition to altering the characteristics of heatwaves, climate change is also leading to a shift in temperature distribution throughout the year and a marked increase in summer temperatures. Santé publique France collaborates with the MCC Collaborative Research Network (an international network of climate and health studies), which has, for the first time, estimated the current influence of climate change on heat-attributable mortality. The analysis^³ was conducted in 732 cities worldwide, including 18 French cities, by combining climate and epidemiological models. It shows that 37% of heat-related deaths between 1991 and 2018 resulted from climate change. The magnitude is the same in France and confirms that climate change already has measurable effects on health. Projections for the future highlight that we should expect increasingly frequent, prolonged, and intense heatwaves, along with a rise in associated mortality, particularly if global warming exceeds +2°C.

These findings underscore the need for systemic transformation to help us learn to live with our new climate (adaptation), while implementing the necessary measures to limit warming (mitigation). These transformations would also have positive impacts on health. Therefore, since 2020, Santé publique France has been developing an approach to draw the attention of policymakers and the public to these issues through targeted advocacy activities. A strategy is thus being developed to promote heat adaptation measures in addition to the prevention messages disseminated during heat waves, and to encourage substantive, sustainable, and equitable actions, particularly regarding the urban environment, buildings, and occupational health. These ideas are also being shared internationally, with extensive exchange of experiences among public health agencies, IANPHI (International Association of National Public Health Institutes), and the WHO (World Health Organization).