Forty Years of Heat Waves in France: A Tale of Climate Change and Health

Abstract

Introduction: Heat waves are the most emblematic health risk directly influenced by climate change. This study documents changes in heat waves' characteristics between 1974 and 2013 in France, the associated mortality impacts, and the influence of the national heat prevention plan developed in 2004.Method: Daily temperature and mortality data were collected for the 96 metropolitan French departments. The French heat warning system definition was used to identify heat waves. Each heat wave was characterized by its duration, intensity (compared to warning thresholds), and associated excess mortality (compared to the previous years). We investigated if the association between mortality rates and intensity changed after 2004.Results: 921 heat waves were identified. The population exposed to dangerous heat waves has doubled between 1974-1983 and 2004-2013. There is no increasing trend in intensity. The mean intensity of the 2003 heat waves was 2-fold higher than any other event, underlying its exceptionality.We observed 31,661 [27,110: 36,188] excess deaths during the 921 heat waves, 45% before 2003, 48% in 2003, and 7% after 2003. The relative risk of mortality for a 1°C increase in intensity was 1.12 [1.11:1.14] before 2003, and 1.13 [1.10:1.17] after 2003.Discussion : Changes in frequency, geographic and temporal spread of heat waves are already observed in France, increasing the exposure of the population. Results do not support an influence of the heat prevention plan on the intensity-mortality relationship at the department scale. The year 2003 remains a unique year with no historical equivalent, and is an example of what may occur in the future. The health impacts of heat waves are the main observable health impacts of climate change. Developing easy-to-understand indicators to observe and describe their evolution is an asset to promote adaptation and mitigation policies.