Hot cities, cool fixes: how to beat the urban heat trap

 

Now that the summer is coming to a close and Belgian rainy days are making a comeback, it’s worth looking back at how cities around the world endured yet another season of extreme heat. In June 2025, parts of the Balkans already saw temperatures soar to 40°C. Across the Atlantic, a persistent heat dome kept much of North America sweltering, with cities like Boston and New York reaching dangerous highs. Closer to home, Belgium and the Netherlands experienced heatwave conditions even before summer had officially begun.

These patterns are no longer exceptions. Earlier, longer, and more intense heatwaves are becoming a structural feature of our climate. Yet not all places heat up the same. Urban areas, with their concrete and asphalt, trap and radiate more warmth, staying hotter for longer. This well-documented phenomenon has a name: the urban heat island effect.

What is the urban heat island effect

Cities contain large amounts of heat-retaining material: asphalt, concrete, metal and glass. These surfaces absorb solar radiation and release it slowly after sunset. At the same time, cities lack cooling elements like trees, open soil and water. The result is higher average temperatures than in surrounding rural areas, especially at night.

 

The effect is well documented. In many cities, urban temperatures are 3 to 5 degrees warmer than their hinterlands. The impacts are significant. Health systems come under pressure. Air conditioning demand rises. And inequality increases, as vulnerable populations often live in poorly insulated buildings with limited access to green space.

Four mitigation measures

Cities don’t have to accept rising summer heat as an inevitability. While extreme temperatures are becoming a structural feature of our climate, there are practical measures that can make urban life more bearable. Many of these solutions are low-cost, relatively simple to implement, and bring multiple co-benefits. What they all share is the need for clear regulation and a long-term perspective.

• White roads: Painting roads with reflective white coatings lowers their surface temperature by up to 10°C. The approach is low-cost and already used in cities like Los Angeles. In dense city environments, this reduces both ambient temperature and the urban energy footprint.
• White roofs: The same principle applies to rooftops. Conventional roofs absorb heat. White or reflective roofs can lower indoor temperatures by 2 to 3°C. That reduces cooling needs and peak electricity demand, especially in poorly insulated homes.
• Rewilding: Nature-based solutions under the label of urban rewilding are gaining traction. Trees, green corridors, miniature forests and pocket parks cool the city through shading and evapotranspiration, even on fragmented plots. Water features such as fountains and shallow ponds add further cooling via evaporation. Importantly, research in Flanders shows that nature outside the city can still reduce urban temperatures, with cooling effects reaching up to 2 km beyond its borders.
• Future-oriented design standards: Cities must rethink their design codes. Heat mitigation should be integrated in architecture and urban planning. This includes minimum shading requirements in public space, sun orientation controls in housing codes, and incentives for passive cooling design. Retrofitting existing stock is a long process. Aligning future buildings with climate projections is faster and more cost-effective.

The Way Forward

The urban heat island effect is not new, but it is becoming increasingly costly. Heatwaves are no longer anomalies, they are part of the baseline. Cities that invest in smarter building standards, greener public spaces, and climate-proof infrastructure will protect public health and reduce long-term economic stress.

The good news: the tools already exist. What’s needed now is the will to put them to work.

At Ortelius, we help cities and regions look ahead: mapping economies in transition and designing the strategies needed for resilience. Learn more at https://ortelius.be.