Excessive heat causes up to about 1,000 deaths annually in the 36 municipalities of the Barcelona area, according to a study by the Institut Metròpoli for the Metropolitan Administration. The work has analyzed the impact of climate change on health during the hottest months, specifically between May 15 and October 15 in this territory during the period 2002-2022. This research calls for the implementation of adaptation policies aimed at the population during extreme heat episodes, especially when intense heat levels exceed 32 ºC.
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Mortality in the metropolitan area due to warming has been showing an “upward trend” in recent years, according to this work, led by Elena Domene.
In fact, deaths increased from 9,237 in 2003 to 10,922 in 2022.
In these exact 21 years, deaths attributable to heat have been estimated at 10,218.
The evolution is not strictly linear over these two decades, but in years with extreme heat episodes (2003, 2019, and 2022) higher mortality values are observed.
An average of almost 500 deaths per year in these decades
The number of heat-related deaths in the metropolitan area shows different behaviors depending on the year. Specifically, the years with the highest mortality attributable to extreme heat were 2003 and 2022, with 957 and 1,060 deaths respectively, a circumstance that coincided with periods of hotter summers.
Conversely, the years 2007 and 2014 recorded the lowest values (around 300), which is associated with cooler summers. Even in years with few deaths for this reason, the amount “is not negligible,” as they can still have health effects.
Over the entire period, an average of 490 deaths per year has been calculated, with a particularly increasing trend from 2015; all this “in parallel with the observed increase in maximum summer temperatures and the higher frequency of sustained heat episodes.”
Heat is also an important cause of total mortality in the metropolitan area, as it is estimated to have been responsible for 9% of total deaths in 2003 and nearly 10% in 2022.
The risk increases rapidly from the 32°C threshold
The intensification of extreme temperatures in the metropolitan area over the last two decades is also highlighted, confirming the already known trend of lengthening periods of intense heat beyond the months traditionally associated with summer, traditionally August.
The results of this work show that the mortality risk remains stable up to temperatures close to 30ºC but increases rapidly from 32°C, and records significant increases from 36ºC where “very significant increases” occur.
62% of deaths are women, and 45% are over 65 years old
During this entire period, excessive heat is estimated to have caused many more deaths among women; specifically, 3,967 deaths of men and 6,436 of women were recorded in the Barcelona area.
Women therefore systematically show higher mortality than men, as they account for 62% of deaths (6,436 of 10,403), a fact related to women’s life expectancy, which is higher and, therefore, they are the majority in the most vulnerable ages.
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In the most critical year, 2022, about 423 deaths in men and about 650 deaths in women are estimated, well above the period average.
The older population also concentrates most of the deaths. Mortality clearly increases with age, as in the entire analyzed period 45% of deaths correspond to the age group between 65 and 84 years. In 2022, about 740 deaths are estimated in the population aged 85 and over, which corresponds to approximately 70% of total deaths.
From 32ºC things change and worsen
The results of this work show that the mortality risk increases rapidly from 32°C, and records significant increases from 36ºC where “very significant increases” occur. These results align with the thresholds marking the health impact of high temperatures for the province of Barcelona by the State Meteorological Agency (Aemet). They indicate that in the Barcelona pre-coastal area (which includes the metropolitan area) the threshold temperature is 33.3ºC; that is, from this level a significant increase in deaths is observed. “This pattern reinforces the need to apply adaptation policies aimed at the population during extreme heat episodes,” especially when intense heat levels are exceeded. It should be noted that the risk thresholds observed in this study (based on the so-called Gasparrini method) and those published by Aemet do not have the same methodology and therefore are not expected to fully coincide.
In the case of this study, to obtain these levels of mortality attributable to excessive heat, an epidemiological model is used that estimates the relationship between temperature and mortality in the analyzed period (2002-2022) so that the point where the risk begins to increase significantly is identified and indicated. In contrast, Aemet’s thresholds are established with an operational criterion for risk management, based on climatic zones and validation of previous studies. Despite the differences, the results are consistent, as this Metropoli study points to the inflection point at 32ºC, very close to the 33.3ºC threshold set by Aemet for the Barcelona pre-coastal area. “Action should be taken when these values are exceeded,” concludes this work.
The incidence is higher in the most densely urbanized areas
The research also confirms that heat increases mortality, especially in densely urbanized areas, due to the heat island effect.
Additionally, the population living in areas with a very high climate change vulnerability index (IVAC) shows greater increases in mortality. (This index is established based on variables such as income, population over 65 years old, proximity to green spaces, and age of housing).
And to establish this classification, any municipality with a census section with very high vulnerability is considered a high IVAC municipality.
Specifically, Barcelona, Badalona, Cornellà, Esplugues, l’Hospitalet, Montcada i Reixac, Sant Adria, Sant Boi, and Santa Coloma de Gramenet have this consideration.
In these municipalities, the rate reaches 3 deaths per 1,000 inhabitants, compared to about 2 cases in the rest, reinforcing the relationship between structural vulnerability and the impact of heat.
Vulnerability is greater in areas with old housing, little green infrastructure, and an aging population
Heat does not affect all metropolitan territories equally. People living in coastal municipalities have a higher risk level against heat than those in inland municipalities.
Vulnerability to heat is greater in areas with old housing, little green infrastructure, and an aging population (where women predominate due to their higher life expectancy), while income and educational level act as protective factors.
The study warns of the urgent need to strengthen adaptation policies to protect the health of the population, especially the most vulnerable, in a Mediterranean context increasingly exposed to climate change.
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