The increase in mortality during the winter months, mainly due to diseases of the circulatory and respiratory systems, is a well-known phenomenon on which there is much evidence. The form and magnitude of the relationship between mortality and ambient temperature depends on several factors, among which the characteristics of the study population and study area stand out.
Not only cold, but also extremely high temperatures, are associated with increased mortality, as episodes known as “heat waves” have been associated with increases in mortality. The available evidence suggests that the relationship between ambient temperature and mortality forms a V-shape, with the lowest mortality rates being recorded on days when the mean temperatures range between 16 ºC and 28 ºC, depending on the climate of the area under study. An important aspect to be considered is the delayed effect of temperature changes on mortality.
The potential impact of rising temperatures due to climate change on health should also not be ignored. In this sense, in 2022 the excess mortality in Spain was the third highest, only surpassed by 2020 and 2015. This excess mortality has been attributed not only to the direct and indirect effects of the COVID-19 pandemic, but also to those of extreme heat episodes, such as heat waves, exceptional in the summer of 2022. However, only 22.92% of the excess in Spain, and 16.22% in Catalonia, has been directly attributed to extreme heat. It is urgent to study the geographical variability of the effect of extreme heat episodes on mortality, estimate what part of the excess can be attributed to extreme heat, the direct and indirect effects of COVID-19 and other causes, as well as the confounding or modifier of the effect of air pollution and socioeconomic factors.