Description du sujet de thèse

Summary:
Both heat waves and wildfires have significant impacts on human health. Increasing evidence warns that climate change will generate more prolonged and frequent heatwaves leading to concomitant heat-driven large fire events. Yet, a multi-risk assessment of these events combined together and their human health impacts is lacking. We leverage complementary skills between UofA (epidemiology) and CNRS (fire/climate science) to assess the current exposure and vulnerabilities of human populations to this combined hazard. By assembling epidemiological information, historical daily climate and extreme event indices, remotely sensed fire types and smoke plume, we will question i) the differential effects of fire characteristics on human health, ii) the potential multiplicative effect of concomitant heatwave and wildfire considering the counterfactual winter prescribed burnings, and iii) the differential vulnerabilities of exposed populations across continents. We will then assemble the scientific basis for management strategies on mitigating climate change impact on human health in fire-prone regions.
Project description and objectives:
Climate change is globally inducing a warmer climate with increasing extreme events (Dosio et al. 2018) and the last decade was the hottest in recorded history with 2023 the hottest year on record (NOAA 2023). Between 2023-2024, 76 extreme heat waves spanning 90 countries were recorded (Arrighi et al. 2024), with an estimated 35% increase in mortality risk for every 1°C increase in temperature (Faurie et al. 2022). Billions of people are at risk with the impact likely to increase given 37% of heat-related deaths are attributable to human-induced climate change (Vicedo-Cabrera et al. 2021; WHO CC 2023). Concomitantly, extreme fire weather is also expected to increase (Quilcaille et al. 2023), driving increased wildfire frequency, duration, and intensity/severity (Abatzoglou et al. 2016; Zhuang et al. 2021). These wildfires affect the health of populations exposed directly to the fire through burns, injury, mental health, and loss of property and indirectly yielding multiple negative health effects of wildfire smoke (see Grant and Runkle et al. 2021 for review), including well established associations with respiratory health and mounting evidence for cardiovascular and other health outcomes (Reid et al. 2016; Casico et al. 2018; Finlay et al. 2012). The hazardous components released during combustion make wildfire smoke more harmful than industrial activities and car emissions (Aguilera et al. 2021; Xu et al. 2020). This leads to significant health burden during fire events including most developed countries such as the USA and Europe (Ma et al. 2024, Chowdhury et al. 2024).
We question here the dual impact on health these events will have, particularly when future climate scenarios forecast increasing large fire events occurring at the same time as heatwaves (Ruffault et al. 2020). As a stunning example, the summer 2022 in Europe, led to heat-related additional mortality (Beck et al. 2024, Ballester et al. 2024, Salesse 2024) and was associated with extreme fire events (Rodrigues et al. 2023). Recent work from the tropics suggests heatwaves and wildfire smoke are more harmful when combined than taken separately (White et al. 2024, Utajug et al. 2024, Bansal et al. 2024, Coker et al. 2024). Given that burned areas increased despite enhanced expenditures and fire fighting capacities (D'Evelyn et al. 2022), we are at a crossroad regarding health effects and wildfire risk management under current climate change and we need to develop a new strategy that measurably reduces threats to communities. This has led our team to bring together fire scientists, climatologists and epidemiologists from UofA and CNRS to ask the questions: i) Does what burns matter for smoke exposure? ii) Do dual hazards induce multiplicative impacts? iii) Are the impacts locally buffered by societal behaviour or environment?

Aim 1. Does what burns matter? The UofA team recently completed a systematic review of 16 studies on 80 cardiovascular outcomes and wildfire exposure. Based on air quality measurements (e.g., Air Indicator Report for Public Awareness and Community Tracking (AIRPACT-4); US Environmental Protection Agency's Air Quality System (AQS)), UofA found that fuel type, rather than PM2.5 or smoke density may elucidate previously unrecognized associations between wildfire and complex etiologies like cardiovascular health. However, uniform and consistent information about wildfires including duration, extent, severity, and fuel type is lacking, preventing deeper analysis. The CNRS team, however, has been developing the global fire event dataset FRY (Laurent et al. 2018) from which this finer resolution information about what burned in a wildfire can be comprehensively described, as well as combustion conditions as fire intensity, days of spread and vegetation affected from remotely sensed coarse resolution global burned area available since 2000. Aim 1 of this proposal will be to assemble the fire events concomitant to the previous systematic review, based on the updated FRYv20, including biomass burned, fire propagation, intensity/Severity and duration/timing and smoke plume as performed in Vallet et al. (2025), to re-analyze the association with cardiovascular disease.
Aim 2. Are dual hazards multiplicative? The risk of human exposure to wildfire and extreme heat is increasing (Intergovernmental Panel on Climate Change 2022: AR6 Climate Change 2021: impacts, adaptation and vulnerability. Working Group II Contribution to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change). However, despite that these stressors in combination are more severe than individually and that the frequency of these dual exposures will increase due to the changing climate, there is little to no work to simultaneously investigate multiple hazards. Focusing on Mediterranean ecosystems of southern France/North Africa, encompassing hot/dry Saharan winds leading to major wildfires (Belhadj-Khedher et al. 2020), and the Southwestern US, we will compare health outcomes associated with fire and heat in combination compared with singly. We'll differentiate fire weather types (heat vs wind driven) as in Ruffault et al. (2020) using ERA5-Land daily climate data for heatwave characterization (Perkins and Lewis 2020, Xu et al. 2018). We'll also investigate winter fires from prescribed burning as a counterfactual 'cold' fire type proposed as a fire management strategy mitigating health fatalities during summer 'heat' fires.

Aim 3. How do local responses buffer? Human exposure to extreme events might differentially impact certain communities, with segments of society becoming more active in response. However, hazard-specific messaging, when hazards overlap, can inadvertently create conflicting messages (Keegan et al. 2021). There is a need to develop social science-based approaches to understand public perceptions of wildfires/heat risk and mitigation efforts, including how to influence human behaviour to reduce vulnerability. Furthermore, there is limited guidance on reaching hard-to-reach-communities (Heaney et al. 2021, Rowitt & Brown, 2022). Using the data from project 2, we will describe, with participatory approaches, the communities where the risk for single and dual hazards are greatest, identify those communities most vulnerable to dual hazards, to make them become more resilient to wildfires/heat risk and feed directly into policy recommendations, considering social norms within demographic or social groups (Santana et al. 2021). The whole project will bring together decision makers and stakeholders to identify the keystone information on fire/heat impacts on human health issues, and assemble the scientific basis for social acceptance of prescribed burning as an alternative strategy to the current fire fighting strategy reaching its limits under the currently increasing drought/heat climate events.

Contexte de travail

The candidate (M/F), will be co-supervised by Florent Mouillot (fire Scientist, UMR CEFE Montpellier), Adam Ali (fire Scientist, UMR ISEM Montpellier) and Heidi Brown (Human health Epidemiologist, Univ. Of Arizona, USA), with shared periods between the two universities. The project is financed for 3years and covers travel expenses.
Research activities and competences require major skiils in computing and statisitcs, in order to cover the fields of i) atmospheric sciences as climatology (climate time series analysis and identification of extreme events) and atmospheric circulation modelling and remote sensing of smoke plumes, ii) earth sciences for fire emissions estimates from remote sensing of burned area and land cover, and iii) epidemiological analysis of human health information. R and/or python efficient programming are required skills, with readiness for transdiscplinary approaches and concepts, along with a significant level in written and spoken English.

Contraintes et risques

Most activities will consist in programming and data analysis, yet requiring travels between Arizona and Montpellier. The project is transdisciplinary with contrasted tools, competences and concepts, yet covered by the 3 supervisors to ensure the project feasability.