The Growing Challenge of Urban Heat in Europe
The summer of 2025 has once again been marked by a series of intense heatwaves that have swept across large parts of Europe. These extreme weather events have had a particularly severe impact on urban areas, where the effects of climate change are amplified due to the Urban Heat Island (UHI) effect.
This phenomenon causes cities to be significantly warmer than their surrounding rural areas, often by two to four degrees Celsius. According to Niels Souverijns, a climate expert at VITO in Belgium, this temperature difference is especially pronounced during heatwaves. Data from the European Commission’s Joint Research Centre reveals that surface temperatures in cities can be as much as 10-15°C higher than in rural regions during the summer months.
With almost 40% of Europe's population living in cities and around 70% residing in urban areas, the implications of this trend are far-reaching. The UHI effect poses serious health risks, 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, putting significant pressure on healthcare systems.
One of the most concerning aspects of the UHI effect is that it persists through the night, preventing people from cooling down properly. This lack of nighttime relief can lead to additional health complications, especially for those with pre-existing conditions like respiratory or cardiovascular diseases.
Factors Contributing to the Urban Heat Island Effect
Several factors contribute to the UHI effect, including the widespread use of heat-absorbing materials like asphalt and cement, which retain and radiate heat throughout the day and night. Wim Thiery, a climate scientist at VUB, explains that these materials are responsible for making cities warmer than their surroundings. In addition, tall buildings and narrow streets trap heat, limiting natural airflow and reducing the city’s ability to cool itself.
Poor urban planning and socio-economic disparities also play a role. In many cities, lower-income neighborhoods often lack green spaces, proper insulation, and access to cooling options. Thiery notes that wealthier areas tend to have more trees and parks, creating a stark contrast in temperature and livability. For example, in Brussels, the poorest districts suffer from a severe shortage of greenery, exacerbating the heat island effect.
The size of the city and the amount of concrete and buildings also influence the intensity of the UHI. Larger cities with dense infrastructure are more affected, as they have fewer natural elements to mitigate heat. Additionally, traffic contributes to the problem, as vehicle emissions act like a greenhouse gas layer, trapping heat and worsening conditions.
Green Solutions and Urban Adaptation
Climate scientists warn that the UHI effect will likely become more severe in the future due to ongoing climate change. Thiery points out that temperatures in Europe are expected to rise by more than 2°C, with heat days becoming up to 4°C warmer. To combat this, cities must adopt a range of strategies, including the creation of wind corridors, green roofs, and increased vegetation.
Souverijns emphasizes the need to redesign cities to reduce concrete and increase green spaces. In the City of Brussels, efforts are already underway to make the environment more resilient. Residents are provided with interactive maps that highlight drinking water points, shaded areas, and other safe havens during heatwaves. The city is also focusing on planting trees, softening surfaces, and integrating more water into urban spaces to create green-blue networks.
Frederik Ceulemans, alderman for climate in the City of Brussels, highlights the importance of sustainable building renovations, which account for 60% of CO2 emissions in the region. The city aims to reduce emissions by 55% by 2030 and achieve climate neutrality by 2050.
The Need for Mitigation and Global Action
While adaptation measures are essential, both experts stress that they are not sufficient on their own. Thiery explains that even with local interventions like tree planting, the impact is limited, as neighboring areas may still experience high temperatures. He argues that mitigation efforts—such as reducing emissions—must be prioritized to prevent further escalation of the problem.
Souverijns agrees, warning that without drastic reductions in carbon emissions, cities could face an "unlivable" future. He points to examples in India and equatorial countries, where extreme heat is already affecting daily life and survival. The challenge is clear: addressing the urban heat island effect requires a combination of immediate adaptation and long-term mitigation strategies to ensure the sustainability of urban environments.