21 consecutive days at risk due to high temperatures: this is how health alerts have been triggered in the major Spanish cities

One day. And another. And another. And another. And another. And so on, up to 21. Three of the most populated cities in the country —Madrid, Barcelona and Zaragoza— have had health alerts active for 21 consecutive days due to high temperatures between July 23 and August 12. Barcelona was still on alert on Tuesday, August 13. But the most striking case is that of the capital and the municipalities of its metropolitan area, located in a weather zone that has had the maximum risk warning active (there are three levels of danger) for 14 days. days, that is, 64%.

The so-called meteo-health zones are areas of territory within a province made up of several municipalities that are homogeneous in terms of the behaviour of daily temperatures. In its latest plan for prevention against high temperatures, the Ministry of Health has divided the country into 182 of these zones, and in each one it has studied from which maximum daily temperature the mortality rate is statistically significant. The system establishes three layers of danger: level 1 (low risk), level 2 (medium risk) and level 3 (high risk). To calculate it, the temperatures predicted for the following 72 hours are taken into account and how close they will be to the thresholds for triggering mortality due to heat.

Only one of the meteohealth areas in which the ten cities with the most inhabitants in Spain are located – where 9.3 million people live, almost 20% of the population, although during the summer the population fluctuates a lot – has not been under a single day of health alert since July 23. This is the area called North of Gran Canaria, where the city of Las Palmas is located. The Canary Islands archipelago has so far been spared from the episodes of high temperatures that have ravaged most of the Peninsula and the Balearic Islands since the second half of July: after a mild first, the heat was very intense from the 18th, and on the 23rd the first wave of the summer began, according to AEMET.

In some cases, such as Madrid, there has been almost no respite and it has become extremely difficult to sleep at night. On Tuesday 13 August, the streak had finally been broken and most of the map of Spain was green (there were only warnings in three major cities: Barcelona, ​​Alicante and Malaga).

Episodes of high temperatures, such as heat waves, are increasing in intensity and duration across the planet (Spain is no exception) driven by the climate crisis that has been triggered by humans, mainly, with the burning of fossil fuels. This same crisis is what has led to the record for the hottest day on the planet being broken this July. It was July 22, according to the latest data from NASA and Copernicus. It is not a one-off or anecdotal record, but is part of a pattern of global temperature increase that has already made 2023 the warmest year on record so far. Experts believe that this record will not last long: 2024 is already shaping up to be the hottest year on Earth.

Cities, where half of the world’s population is concentrated, are the setting in which this climate emergency is brewing, which has a clear impact on public health. The IPCC (Intergovernmental Panel on Climate Change) has its sights set on cities. This group, linked to the UN and which has periodically reviewed and updated scientific knowledge on climate change since 1988, is already preparing its seventh cycle of reports. And it has just been approved that the first of the reports, which will be published in March 2027, will be a special report on cities and climate change which will address mitigation and adaptation strategies to global warming.

Cities are victims and executioners of a crisis that shows one of its most recognizable faces during episodes of high temperatures. The heat island effect, which prevents cooling, causes warm nights that are dangerous for health. joint research A study by the CSIC and the Carlos III Health Institute in five Spanish cities with high population density (Madrid, Barcelona, ​​Valencia, Malaga and Murcia) found average variations in minimum summer temperatures between the interior of the city and the outskirts. These differences ranged from 1.3 degrees in Madrid to 4.1 degrees in Valencia, and reached 11 degrees on the most extreme days. It was also found that the heat island effect is more pronounced in coastal cities than in inland cities, probably as a result of humidity.

When mortality and emergency hospital admissions are studied, it is found that it is in these cities where warm nights have the greatest impact, while in inland cities it is the maximum temperatures that cause the most morbidity and mortality. Climatologist Dominic Royé explains that one of the reasons behind this may be that the cardiovascular system, which works to reduce body temperature and thus lead to sleep, does not succeed: “To sleep well we need our heartbeat to drop, but in the heat this is more difficult, which can cause dangerous stress for vulnerable people.”

María Ángeles Bonmatí, postdoctoral researcher at Ciberfes (Carlos III Health Institute) and also author of the book Let nothing take away your sleep, He adds that not sleeping enough or of good quality for several days can also affect cognitive and physical performance: “We concentrate worse, it affects our mood, we are more irritable, any small conflict is a big problem, in addition to weakening our health.”

Lack of sleep weakens the immune system, makes it easier to contract infections and has an indirect consequence that can be fatal: it causes work and traffic accidents. The DGT calculates that 7% of fatal road accidents are due to drowsiness, which means at least 75 deaths and 250 seriously injured people each year.

As Carmen Bellido, a doctor specialising in occupational health and a member of the Sleep Alliance, warns, it is precisely in summer, the time when the heat prevents us from sleeping, when there are more road trips and there is a greater chance of having an accident. “Sleep is life,” says this doctor, who warns of another possible negative consequence of losing sleep due to hot nights, which are especially common in cities: “It is a time when bad habits can be established. When we start to sleep poorly, we may get used to getting up to eat something, to pick up our mobile phone, or start taking inappropriate medication. And, without realising it, a person who slept well may find themselves with a sleep problem that becomes chronic.”

Apart from traffic accidents, extreme temperatures have an impact on health that can be fatal. Heat stroke is the most extreme case, but it is only the tip of the iceberg. The Ministry of Health recorded 24 deaths from this cause last year (three were reported in the heat wave that just ended, reports EFE). But deaths linked to heat due to the worsening of other ailments in the population at risk would rise to 8,352, according to a study published this Monday in the journal Nature Medicine. It is the imbalance in the body that causes the most vulnerable people (especially the elderly or very young children) to suffer problems (cardiac, metabolic and renal, among the most frequent) that can lead to hospitalization or even death.

That same publication estimated that more than 47,000 people died in Europe as a result of high temperatures in the summer of 2023. But the researchers from the Barcelona Institute for Global Health (ISGlobal), responsible for that article, go further and calculate the benefits of adaptation to high temperatures in recent years. They estimate that if the temperatures recorded in 2023 had occurred at the beginning of this century, heat-related mortality would have exceeded 85,000 deaths, that is, 80% more. “This is due firstly to individual behaviour; people are now more aware of the negative effects of high temperatures,” explains Marcos Quijal, one of the ISGlobal researchers who participated in the study. “It is also due to public health measures, which cause heat alerts to be activated when extremes occur,” he adds.

But more is needed on a planet that continues to warm and in cities where the heat island effect exacerbates the problem even more. One of the remedies that science clearly points to is green spaces. “Trees make temperatures cooler and reduce the exposure of the most vulnerable population groups,” says Quijal. “It is also very important to reduce traffic,” adds this researcher. “We are increasingly having hotter summers with more intense and longer-lasting heat waves, so the role of adaptation in societies is very important, especially for the most vulnerable population groups,” concludes Quijal.

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