Barcelona faces extreme heatwave surge by 2100

Summary:

Heatwaves in the Metropolitan Area of Barcelona could become up to 6ºC more intense by the end of the century, according to a study published in the Journal of Geophysical Research: Atmospheres. Conducted by the Institute of Environmental Science and Technology of the Universitat Autònoma de Barcelona (ICTA-UAB), the research projects how recent heatwave episodes might evolve under future climate scenarios using high-resolution meteorological modeling. The team applied the Pseudo Global Warming (PGW) method to simulate past heat events under conditions expected by mid-century (2041–2070) and end-century (2071–2100) based on the SSP3-7.0 scenario, which assumes limited emission reductions and rising global conflict.

The results point to a sharp rise in maximum and minimum temperatures – potentially exceeding 45ºC in inland urban areas and 42ºC in parts of Barcelona. Relative humidity is projected to fall, and nighttime cooling could become increasingly rare, especially in coastal zones. The study also identifies a rise in geopotential height at 500 hPa as a key driver of atmospheric stability, increasing the likelihood of persistent extreme heat. These projections highlight the vulnerability of densely populated urban areas and support the case for accelerating climate adaptation measures in cities.

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Barcelona could suffer heatwaves up to 6ºC more intense by the end of the century

Heatwaves that already affect the population of the Metropolitan Area of Barcelona (AMB) could significantly intensify in the future, with temperature increases of up to 6ºC and a general reduction in relative humidity in cities by the end of the century. This is shown in a study carried out by the Institute of Environmental Science and Technology of the Universitat Autònoma de Barcelona (ICTA-UAB), which warns of an increase in average maximum temperatures of 4ºC and average minimum temperatures of 3.5ºC if greenhouse gas emissions are not drastically reduced. Temperatures could reach values above 45ºC in urban inland areas of the AMB and above 42ºC in interior areas of the city of Barcelona.

The research focuses on heatwave episodes in the AMB over the past 30 years (1991-2020) and projects these events towards the middle and end of the century. Using the Pseudo Global Warming (PGW) method and high spatial resolution urban meteorological modeling (1 km), the study simulates how the most common meteorological conditions recorded in recent decades would evolve if repeated under the climatic conditions forecast for mid-century (2041–2070) and end-century (2071–2100).

The researchers considered a scenario in which regional and global conflicts continue, and the reduction of greenhouse gases remains not a priority, thereby producing an expected rise in CO₂ emissions to nearly double that of current levels by 2100.

The study allows identifying which meteorological conditions would be altered to a greater or lesser extent by global warming. The results show a notable increase in maximum temperatures and the “urban heat island” effect, particularly in cities, as well as a reduction in relative humidity and changes in sea breezes.

The main results of the study are as follows:

Temperature increase:

• Maximum temperatures could increase by an average of 4ºC and minimum temperatures around 3.5ºC by the end of the century.
• Under especially stable atmospheric situations, increases of up to 6ºC are projected to be reached by the end of the century.
• Thus, maximum temperatures could reach above 45ºC in urban inland areas of the AMB and above 42ºC in interior areas of the city of Barcelona. Minimum temperatures in coastal areas would not drop below 32ºC within the city of Barcelona by the end of the century.
• The greatest temperature increases would occur in urban areas, probably due to the high absorption of radiation by artificial materials and poor ventilation caused by regional and large-scale winds. Additionally, this situation would occur in late summer conditions with a warmer Mediterranean Sea, which would also lead to higher minimum temperatures in coastal areas.

Reduction of relative humidity:

• An average decrease of 6% in relative humidity for maximum values and 5.3% for minimum values is expected, with reduction peaks of up to 16% in the Garraf area, possibly due to alterations in sea breeze behavior.

Increase in geopotential:

• Geopotential height at 500 hPa could increase up to 100 meters, which translates into a warmer atmosphere. This would occur more notably in the eastern area of the Iberian Peninsula and especially in the Mediterranean, indicating a more stable atmosphere prone to persistent heatwaves.

“Our study is the first to combine the PGW approach with high-resolution urban simulations in Barcelona. This combination allows capturing the urban heat island effect and projecting more precisely how heatwaves will worsen over the next 75 years,” explains Sergi Ventura, ICTA-UAB researcher and lead author of the study.

The Metropolitan Area of Barcelona, which concentrates more than 3.3 million inhabitants in barely 636 km², already shows clear signs of climate vulnerability. In recent heatwaves, increases in mortality of up to 27% have been observed. Although future episodes could be accompanied by lower relative humidity — which could reduce perceived thermal stress — nighttime heat will remain a critical risk factor.

“Since more than half of the world’s population lives in cities, it is crucial to understand how future extreme events, such as heatwaves, will affect these urban areas,” highlights Ventura. The study reinforces the urgency to advance adaptation plans, such as the Barcelona Climate Plan, which aims for a 40% emissions reduction by 2030 (compared to 2005), and measures like the creation of 1.6 km² of new green spaces, green roofs, and promotion of public transport.

Ventura highlights the innovative use of the Pseudo Global Warming technique to “transport” past events to future conditions. It also uses a detailed urban simulation with 1 km resolution, including urban parameters such as land use, urban materials used, and vegetation.

It also analyzes the sensitivity to global warming of the most common large-scale meteorological patterns in heatwave cases in the Metropolitan Area of Barcelona found in previous studies.

Journal Reference:
Ventura, S., Miro, J. R., Segura-Barrero, R., Chen, F., Martilli, A., Liu, C., et al., ‘Assessing the intensity of heatwaves in a warming climate at the urban scale: A case study of the metropolitan area of Barcelona’, Journal of Geophysical Research: Atmospheres 130, 14: e2025JD043559 (2025). DOI: 10.1029/2025JD043559

Article Source:
Press Release/Material by Universitat Autonoma de Barcelona (UAB)
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