Comparison of various heat waves definitions and the burden of heat-related mortality in France: Implications for existing early warning systems
Fleur Serge Kanti, Anna Alari, Basile Chaix, Tarik Benmarhnia
Abstract
In France, a heat warning system (HWS) has been implemented almost two decades ago and rely on some official heat wave (HW) definitions. However, no study has compared the burden associated with a large set of alternative HW definitions to the official definitions. Such comparison could be particularly helpful to identify HW conditions for which effective HWS would minimize the health burden across various geographical contexts and possibly update thresholds to trigger HWS. The aim of this study is to identify (and rank) definitions that drive the highest health burden in terms of mortality to inform future HWS across multiple cities in France. Based on weather data for 16 French cities, we compared the two official definitions used in France to: i) the Excess Heat Factor (EHF) used in Australia, and ii) 18 alternative hypothetical HW definitions based on various combinations of temperature metrics, intensity, and duration. Propensity score matching and Poisson regressions were used to estimate the effect of each HW exposure on non-accidental mortality for the May–September period from 2000 to 2015. The associations between HW and mortality differed greatly depending on the definition. The greatest burden of heat was 1,055 (95% confidence interval “CI”: [856; 1,302]) deaths per summer and was obtained with the EHF. The EHF identified HW with 2.46 (95% CI: [1.92; 3.58]) or 8.18 (95% CI: [6.63; 10.61]) times the global burden at the national level obtained with the climatological indicator of the French national weather service and the HW indicator of the French national HWS, respectively and was the most impactful definition pattern for both temperate oceanic and Mediterranean climate types. Identifying the set of extreme heat conditions that drive the highest health burden in a given geographical context is particularly helpful when designing or updating heat early warning systems . French cities included in the study and their climate, and heat-related deaths estimated with a large set of heat wave definitions (May-September, 2000-2015). The definitions are the Excess heat factor of the Australian Bureau of Meteorology (hw_EHF), the climatological indicator of the French national weather service (hw_MF), the heat wave indicator of the French national heatwave warning system (hw_SACS), and the others based on the temperature parameters, which are presented in the format as follow: (heatwave)_(temperature)_(percentile)_(minimum number of consecutive days). For example, hw_min_95_2d defines a heat wave if the minimum temperature was above the 95th percentile of the minimum temperature for at least two days. • Heat-related mortality was assessed on relative and absolute scales using a large set of heat waves definitions. • Associations between heat waves and mortality differed greatly depending on the definition. • According to the French heatwave warning system indicator, 129 heat-related deaths per summer were estimated. • Excess heat factor was the most impactful definition for the temperate oceanic and Mediterranean climate types.