Summers are getting hotter, especially in cities like Rotterdam, where asphalt and concrete dominate the landscape and trap the heat long after sunset. The consequences are significant: heat stress leads to serious health risks for vulnerable city dwellers like the elderly and pregnant women, and can even affect children’s school performance. Rotterdam’s response to the increasing risks of heat stress? The Rotterdam HeatLab: a joint initiative by local knowledge institutions and the city.
A city warming up
With climate change driving temperatures higher, Rotterdam is bracing for longer, more frequent, and more intense heatwaves in the coming years. Yet the impact of heat is already being felt. Hans de Voogd, director of Resilient Delta and one of the HeatLab’s founders, calls extreme heat a "silent disaster" for the city.
'When rising sea levels become a threat, no one questions the need for immediate action', he says. 'But rising temperatures don’t trigger the same alarm bells. Heat is one of the most underestimated climate risks we face, largely because its effects are less visible than the damage of a flood or storm, for example. But as a society, we need to start recognizing that the impact of heat can be just as devastating.'
Every year, people die from heat stress. Other health risks include dehydration, sleep disturbances, headaches, and impaired concentration. 'The health and livability of the city are already under strain, especially in vulnerable neighborhoods', De Voogd says. 'And we have to prepare for even more extreme scenarios.'
Vulnerable people and neighbourhoods
Heat doesn’t affect every Rotterdammer equally. Professor Lex Burdorf, expert in public health at Erasmus MC, observes large temperature differences within the city itself. 'On hot days, temperatures in some Rotterdam neighborhoods can be five to seven degrees higher than in other parts of the city', he explains. 'That’s a matter of how neighborhoods are designed: some areas have very little greenery or water, and lots of stone and pavement. That makes a huge difference. During a heatwave, you’d rather live near the Kralingse Plas than in Afrikaanderwijk.'
Housing quality also plays an important role. In the most heat-vulnerable neighborhoods, many homes are poorly insulated against heat. 'In these areas, residents don’t just suffer from higher outdoor temperatures,” says Burdorf, “but also from higher indoor temperatures. Heat stress is therefore not just a climate issue—it’s a social issue too. In underprivileged neighborhoods, we see the most severe health effects. Elderly people, the sick, pregnant women, and other vulnerable groups face the greatest risks.'
Living with heat
To better protect the city against the growing heat problem, HeatLab Rotterdam was founded in 2024. The HeatLab, an initiative by Resilient Delta, is a collaboration between the Convergence alliance (TU Delft, Erasmus University Rotterdam and Erasmus MC), Rotterdam University of Applied Sciences, the GGD Rotterdam-Rijnmond and the municipality of Rotterdam.
Rick Heikoop, lecturer-researcher at Rotterdam University of Applied Sciences and coordinator of the HeatLab, says heat greatly affects daily life in the city. 'Besides the health risks, we’re also seeing other negative effects during heatwaves. People sleep poorly, their ability to function declines, and there’s more aggression and violence', he explains. 'Children find it difficult to concentrate at school, especially in older school buildings where temperatures in classrooms rise quickly. Even here at the Rotterdam University of Applied Sciences we notice it: classrooms facing south become uncomfortably hot. Teaching and learning become much harder under those conditions.'
According to Heikoop, the effects of heat go further than many people realize. 'The Netherlands simply isn’t designed for heat', he says. Having lived for years in the Philippines, Heikoop knows what it means to organize life around high temperatures. 'For example, schools in the Philippines start very early in the morning and close during the hottest part of the day. At the HeatLab, we’re also looking at those kinds of solutions. Of course we need solutions for greening, cooling and heat-proofing urban spaces, but it’s just as important to think about how we organize daily life in the city.'
Students as catalysts
Within the HeatLab, students play a key role.“Research questions often come from the GGD or the municipality', says Heikoop. 'Students from different institutions and study programs work on these questions. They measure temperatures around the city, study the health effects of heat, or explore ideas for climate-adaptive urban design.'
According to Heikoop, young researchers are a driving force within the HeatLab. 'Today’s students grew up with bleak climate scenarios and a daily stream of negative climate news. That can be paralyzing. But we’re seeing that many students are incredibly motivated to contribute and to work together on solutions. That kind of energy is infectious.'
The first student research projects have already been completed. 'We’re collecting all their research and publishing it on the Heat Lab’s website', says Heikoop. 'That way, knowledge continues to build. New students can pick up where others left off.'
Awareness about heat stress
The question is: what will Rotterdam do with all the knowledge emerging from the HeatLab? The first step is raising awareness, says Hans de Voogd. 'Fortunately, we’re starting to see more attention for the issue. A day like the recent Heat Action Day really helps. It was a day for all Rotterdammers, entirely focused on heat. There was theater, the Erasmus Bridge lit up in orange, there was a heat run, and we organized an inspiring knowledge day where we brought together science, politics and the city.'
During Heat Action Day Rotterdam, held on June 2, 2025, De Voogd and the other HeatLab partners signed a covenant, committing themselves to intensified cooperation to address heat-related challenges in the coming years. 'Collaboration is essential', says De Voogd. “We need each other to tackle the heat problem and to keep the city livable, healthy, and safe for future generations. This isn’t something we can put off for another fifty years until cities become unbearably hot. The time to act is now.'
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The Resilient Delta initiative is one of five programs of Convergence, an alliance between TU Delft, Erasmus University Rotterdam and Erasmus MC. At the Resilient Delta initiative, we collaborate across disciplines to design real-world solutions to the global challenges we face – from climate change to growing social inequality. With the Dutch delta as our living lab, our pioneering research aims to help the Netherlands and delta regions across the world navigate towards a resilient future.
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