It’s not all about the extremes: monitoring heat-associated mortality in England in 2024

Abstract The link between heatwaves and mortality in England is well established, with annual mortality surveillance since 2016. This work explores the impact of heat during the relatively cool summer of 2024, which saw over 1300 heat-associated deaths, despite no Amber or Red Heat Health Alerts. This supports understanding of heat impacts on health even at non-extreme temperatures, and informs progress on climate adaptation. Heat-associated deaths were measured as the difference between observed daily mortality during heat episodes and baseline periods, and disaggregated by age group, sex, place of death and geography. Then, distributed lag non-linear modelling was used to estimate the historic temperature-mortality relationship in England, using data from the previous five summers. The model was applied to 2024's observed temperatures to generate predictions of deaths in each heat episode, which were compared with the observed estimates. Over four heat episodes in 2024, 1311 (95% confidence interval: 929-1692) heat-associated deaths were observed. Across the summer, statistically significant mortality was found in older age groups, in males and females, and in care homes, hospitals and at home. Analysis at regional and subregional level did not reveal clear geographical patterns in mortality rates. Modelling predicted 1028 (866-1155) heat-associated deaths, which was lower than the observed number, though not a statistically significant difference. The model estimates were well aligned with observed deaths for the two later heat episodes, whereas observed deaths were higher in the earlier-season episodes. The findings point to the important role of behavioural and population factors as well as temperature in determining mortality, particularly related to early season preparedness. This informs evaluation of the Heat Health Alerting system and improvements to public health strategies for adaptation to climate change. Key messages • Heatwaves cause significant mortality even without reaching extreme temperatures, requiring public health action to protect those who are vulnerable particularly in care home and hospital settings. • As well as temperature, contextual and behavioural factors play a crucial role in determining mortality, and must be factored in for effective decision making in early warning systems for heat.