This is how urban heat islands affect health

The Reference Unit on Climate Change and Health at the Instituto de Salud Carlos III (ISCIII) published research on the effect of urban heat islands on urgent hospital admissions and short-term deaths in five Spanish cities. The results, obtained after analyzes carried out in Madrid, Barcelona, ​​Valencia, Malaga and Murciaare published in the magazine Total Environmental Science.

The urban heat island effect is called a meteorological phenomenon that results in a temperature rise in urban areas, usually at night. This increase is attributed to bills that contribute to heat buildup during the day. Among them, the materials present in cities such as asphalt, building facades and air conditioning equipment. This phenomenon, added to global warming caused by climate change, can affect people’s health increase the risk of hospitalizations and deaths.

Heat islands are produced by the accumulation of heat during the day on asphalt and facades, as well as by the heat that comes out of air conditioners.

The main results of the work indicate that the thermal heat island effect is observed mainly in minimum temperatures -that is, the nocturnal ones- and not so much in the maximums, and that their values ​​fluctuate a lot depending on the city. In Murcia a difference of 1.2 degrees Celsius is reflected in the city above the periphery, while in Valence is 4.1 degrees.

Furthermore, the authors confirmed that the relationship between the risk of disease and death in inner cities occurs with the maximum temperatures -days-, while this association, in the coastal citiesappears with the minima -the nocturnal ones-.

Location and characteristics of each city

This work uses data from meteorological observatories, one located in cities and another in the outskirts, which has allowed confirm thermal differences of the heat island effect. O wider range of values Between the urban interior and the exterior they have a maximum daily amplitude of up to 11.2ºC in Valencia, 9.5ºC in Murcia and 7.1ºC in Madrid.

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The results indicate that the geographic location and characteristics of each zone are fundamental for the possible effect of the urban thermal island, which suggests the need to conduct local studies determine the greater or lesser importance of this phenomenon according to the type of city.

These heat build-ups pose a greater health risk in coastal cities.

The study points out that in inland cities like Madrid and Murcia the thermal island can cause discomfort in people, but it has less potential health effectssince it does not affect deaths or emergency hospital admissions in the short term.

On the other hand, in coastal cities like Valencia, it is possible to identify increased health risk, with an increase in daily urban minimum temperatures related to deaths and hospitalizations. In Barcelona’s case, both ends of the thermostat seem to have influence.

The work has been led since ISCIII by physicians Julio Diaz It is Cristina Linares and researchers Miguel Ángel Navas and José Antonio López Bueno participated. Scientists from the State Meteorological Agency (AEMET), the Eduardo Torroja Institute of Construction Sciences of the CSIC and the Castilla-La Mancha Health Service also collaborated.


Cuerdo-Vilches, T. et al. “Impact of urban heat islands on morbidity and mortality in heat waves: observational time series analysis of five cities in Spain” Total Environmental Science (2023)

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