The Impact of Urban Heat Islands in Europe
The summer of 2025 has once again been marked by a series of intense heatwaves, affecting large parts of Europe. These extreme weather events have had the most severe impact on urban areas, where temperatures are significantly higher than in surrounding rural regions due to the Urban Heat Island (UHI) effect.
According to Niels Souverijns, a climate expert at VITO in Belgium, cities can be up to four degrees warmer than their rural counterparts during heatwaves. This phenomenon is exacerbated by factors such as the materials used in construction and the concentration of buildings and traffic. Data from the European Commission’s Joint Research Centre shows that surface temperatures in cities can be as much as 10-15°C higher than in nearby rural areas during the summer months.
With almost 40% of Europe’s population living in cities and around 70% residing in urban areas, the implications of these rising temperatures are far-reaching. The UHI effect poses a serious health risk, particularly for vulnerable groups such as the elderly and young children. A study by NOVA National School of Public Health in Portugal found that hospital admissions increased by 18.9% on heatwave days, placing significant strain on healthcare systems.
Factors Contributing to the Urban Heat Island Effect
The UHI effect is primarily caused by the use of heat-absorbing materials like asphalt and cement, which retain and radiate heat throughout the day and night. Climate scientist Wim Thiery from VUB explained that these materials absorb sunlight and release it later, leading to higher nighttime temperatures. Additionally, tall buildings and narrow streets trap heat, reducing natural airflow and making it harder for cities to cool down.
In many cities, the problem is more pronounced in poorer urban areas, where dense and unregulated development often results in limited access to green spaces and cooling options. Thiery noted that wealthier neighborhoods tend to have more greenery, as seen in Brussels, where the divide between affluent and disadvantaged areas correlates with access to trees and parks.
Souverijns added that larger cities with more concrete and buildings are more affected by the UHI effect. Traffic also plays a role, as vehicle emissions contribute to a layer of greenhouse gases that trap heat over urban areas.
Green Solutions for Urban Cooling
Climate scientists warn that the UHI effect is expected to worsen due to climate change, with heat days becoming increasingly severe. However, cities can take measures to mitigate this issue. Thiery emphasized the importance of redesigning urban environments to reduce concrete and increase green spaces. This includes creating wind corridors, implementing green roofs and facades, planting more vegetation, and incorporating water features into city planning.
The City of Brussels, one of the most vulnerable areas in Belgium, has taken steps to address the issue. Residents are provided with interactive maps that highlight places to find drinking water, shaded areas, and other cooling spots. Frederik Ceulemans, alderman for climate in the City of Brussels, highlighted efforts to plant trees, soften surfaces, and create greener, shadier public spaces. Future plans include testing shaded structures, both temporary and permanent, to further combat rising temperatures.
The Need for Mitigation and Adaptation
While adaptation measures can help, experts agree that they are not enough on their own. Thiery pointed out that the impact of local interventions, such as planting trees, is limited. In densely populated areas, there is often insufficient space for widespread greenery. Souverijns echoed this sentiment, stressing that mitigation must be prioritized to prevent future heatwaves from becoming unmanageable.
The City of Brussels is focusing on sustainable building renovations, which account for 60% of CO2 emissions in the region, as well as sustainable mobility and energy plans. The goal is to reduce CO2 emissions by 55% by 2030 and achieve climate neutrality by 2050. If emissions are not reduced to zero, experts warn that cities could face “a tsunami of heat,” making them increasingly unlivable.
Currently, cities in India and equatorial countries are already experiencing similar challenges, where residents struggle to cope with extreme heat. As climate change continues to intensify, the lessons learned from these regions will become even more critical for cities across Europe.