Heat-related deaths in Europe in 2022 revised up

High temperatures may have led to more than 70,000 excess deaths in Europe during the summer of 2022, according to a study published today.

The research, led by the Barcelona Institute for Global Health (ISGlobal), Spain, developed a theoretical framework capable of quantifying the errors arising from the use of aggregated data, such as weekly and monthly temperature and mortality time-series.

It followed their earlier study when the team used epidemiological models applied to weekly temperature and mortality data in 823 regions in 35 European countries and estimated the number of heat-related premature deaths in 2022 to be 62,862.

In that study, the authors said the use of weekly data would be expected to underestimate heat-related mortality, adding that daily time-series data are required to accurately estimate the impact of high temperatures on mortality.

For their latest research, which is published in The Lancet Regional Health – Europe, the team aggregated daily temperatures and mortality records from 147 regions in 16 European countries before analysing and comparing the estimates of heat- and cold-related mortality by different levels of aggregation: daily, weekly, two-weekly and monthly.

The analysis showed differences in epidemiological estimates according to the time scale of aggregation, with weekly, two-weekly and monthly models underestimating the effects of heat and cold compared with the daily model. The degree of underestimation increased with the length of the aggregation period, the researchers report.

Between 1998 and 2004, the daily model estimated an annual cold and heat-related mortality of 290,104 and 39,434 premature deaths, respectively, while the weekly model underestimated these numbers by 8.56% and 21.56%, respectively.

Joan Ballester Claramunt, ISGlobal researcher and leader of the European Research Council’s EARLY-ADAPT project, said: “It is important to note that the differences were very small during periods of extreme cold and heat, such as the summer of 2003, when the underestimation by the weekly data model was only 4.62%.”

The team used this theoretical framework to revise the mortality burden attributed to the record temperatures experienced in 2022 in their earlier study. Using the new methodological approach, they said their earlier study underestimated the heat-related mortality by 10.28%. This would mean the number of heat-related deaths in 2022 was 70,066 deaths, and not 62,862 deaths as originally estimated.

“In general, we do not find models based on monthly aggregated data useful for estimating the short-term effects of ambient temperatures,” said Ballester. “However, models based on weekly data do offer sufficient precision in mortality estimates to be useful in real-time practice in epidemiological surveillance and to inform public policies such as, for example, the activation of emergency plans for reducing the impact of heat waves and cold spells.”

Ballester J, van Daalen KR, Chen Z et al. The effect of temporal data aggregation to assess the impact of changing temperatures in Europe: an epidemiological modelling study. The Lancet Regional Health – Europe 21 November 20232; doi: 10.1016/j.lanepe.2023.100779

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