This summer —from June to August— there have been six days with high temperatures (those that are exceeded only on 5% of summer days) in León, while in Málaga there were 12, double; however, the estimated rate of deaths attributable to heat is three times higher in the first city compared to the second (58 per 100,000 inhabitants compared to 18). The data, obtained through a new scientific application —MACE—, allow us to observe the differences in how the summer weather affects each province: in general, those inland, more rural and older, suffer more than those on the coast or in the south, more accustomed to heat waves.
That heat increases mortality is demonstrated by numerous scientific studies, although measuring exactly how much is more complex: it is usual for this cause not to appear on death certificates, but rather other pathologies that heat makes more deadly. The Carlos III Health Institute (ISCIII) develops the Daily Mortality Monitoring System (MoMo) and estimates how many of these deaths are attributable to extreme heat, which this summer is estimated at 2,190. “It is a statistical model based on provincial temperature thresholds from which mortality attributable to heat, i.e. heat waves, increases,” says Inmaculada León, co-director of MoMo.
Another tool to calculate deaths due to heat, launched a few months ago, is MACE — Mortality attributable to heat in summer in Spain —, which not only takes into account the highest temperatures, but also those moderate ones that exceed the minimum mortality level: around 17 degrees of average daily temperature, for which the maximums must be around 30. MACE —developed by the Foundation for Climate Research (FiClima) together with scientists from the CSIC and the University of Valencia, using figures from MoMo and Aemet as a basis, has developed a model that takes into account the association between temperature and mortality between 2015 and 2023 in each province and then suggests the current probable number of deaths. The differences by province can be explored in the following map.
The data estimate that this summer there have been 2,720 deaths attributable to extreme heat – a figure similar to the approximately 2,200 estimated by MoMo – but adds another 9,163 attributable to moderate temperatures. In total, 11,883, a figure lower than the previous year, 13,471. These are numbers similar to those that appeared in a recent study by IS Global, which estimated them at around 8,700 in 2023. “Moderate heat, any heat that exceeds the comfortable temperature, also affects health, so it makes sense to quantify its contribution to mortality,” says Carmen Íñiguez, a senior lecturer in the Department of Operational Research Statistics at the University of Valencia, and one of the participants in MACE.
The tool has certain limitations: it always uses the 95th percentile of temperature for extreme heat (i.e. a temperature that exceeds it on only 5% of summer days), while the Ministry of Health (through the National School of Health of the ISCIII) calculates the specific heat excess for 182 Spanish regions. On the other hand, the ISCIII does not calculate deaths due to moderate heat, which MACE does.
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25 degrees is not the same in Alicante or in Burgos
Climatologist Dominic Royé, from FiClima and another of those who developed the model, adds: “It is important to measure it like this because, for example, this summer in Valencia there have only been two days of extreme heat, but on the other hand there have been many days that were very close to that threshold, without exceeding it, so they are only counted within moderate heat.”
The model estimates that around 12% of summer mortality is related to high temperatures. The differences are very marked by province: in general, in coastal and southern provinces it is less than 10%, while in inland provinces it can exceed 15%.
There is a fairly direct relationship between the number of days of extreme heat (of which only occur 5% of the days) and the percentage of deaths attributable to heat in each province: Soria has been the area with the most days of temperatures above the 95th percentile and is also the one with the highest percentage of deaths due to heat. In Seville, there have been very few days that exceeded that barrier —and less than 8% of deaths are related to heat—.
But there are cases that go beyond this description. One that stands out – for the better – is Málaga, which has had 12 days above the limit and a fraction of deaths similar to that of provinces that experienced little heat. On the other hand, León is one of the places with the fewest days that exceed the threshold (6) and the fourth province with the highest proportion of deaths (17%).
Royé comments: “In inland regions, it is expected to find a higher percentage due to the ageing of the population, since the elderly are more affected.” Iñiguez adds: “It could be due to many other factors, from socioeconomic factors to the climatic range to which they are accustomed.” For example, with 25 degrees the population of Alicante may be very comfortable, but in Burgos they will already begin to suffer from heat. The researchers remember, however, that there may also be different exposure to heat from one year to another.
Julio Díaz, a researcher at ISCIII and an expert in health and high temperatures —although he has not participated in MACE—, adds more causes: “The population pyramid, income level, housing rehabilitation, urban infrastructure, pollution… are all involved in mortality. It is not the same to be at 38 degrees in a small house with four people than in a chalet with a swimming pool and air conditioning. We did a study which shows that the impact of heat in Madrid is much higher in the districts with lower incomes.” In addition, it points out that the population is acclimatised to the heat – around 0.6 degrees per decade – so it is more likely that the population accustomed to high temperatures will better withstand one of these episodes than those who do not usually experience them. This is a factor to take into account so that a heat wave does not have the same effect in Malaga as in Leon.
Returning to that example, Royé points out: “The average age in Málaga is about 40 years old, while in León it is around 50, which means that there are more very old people, who are the most affected. There may be a differential factor there.” Íñiguez concludes: “Proximity to the coast is a climate regulator, since in general they are less prone to climatic extremes. There are studies that find a reduction in the risk of mortality associated with heat in coastal areas. In addition, proximity to the sea is an adaptation resource that is free, that does not depend on socioeconomic level and that works: anyone can bathe in the sea.”
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