How Built Environments Contribute and Mitigate Urban Heat Island

Temperatures in cities or urban areas are often hotter than those in surrounding rural areas; this phenomenon is known as the Urban Heat Island (UHI) effect.

The difference, which can range from one to seven degrees Fahrenheit, arises from how surfaces in each environment absorb and retain heat.

Infrastructure is a significant contributor to urban heat, but it can also play a part in providing a solution. Built-up areas, such as roads and pavements, which are typically made from concrete, glass, steel, and asphalt, absorb heat and contribute to higher urban temperatures. However, when infrastructure is planned and designed thoughtfully, it can also help cool cities effectively.

The World Resources Institute (WRI) highlights how infrastructure can become a powerful tool for cooling, with examples of solutions already being implemented across cities worldwide to combat rising temperatures, which are further intensified by climate change.

Cooling cities beyond air conditioning

Cooling cities without relying on air conditioning focuses on “surface infrastructure”—the areas where the physical city meets the atmosphere. These include roofs, pavements, car parks, sidewalks, and even building walls.

The key lies in ensuring these surfaces reflect sunlight rather than absorb it. Reflective materials send solar energy back into the atmosphere, helping to prevent warming. Conversely, when surfaces absorb energy, it is later re-emitted as heat, which increases the temperature of the surrounding air.

Growing populations and urbanisation in already hot regions have heightened demand for air conditioning. Even in cooler climates, the expansion of built-up areas and the heat generated by offices and equipment create a need for indoor cooling. Yet air conditioning adds to the problem: while it cools interiors, it increases outdoor temperatures.

As heatwaves become more intense, frequent, and prolonged, they pose serious health risks. Europe’s heatwave in 2003, for example, caused an estimated 70,000 deaths, while the 2015 heatwave in India and Pakistan led to more than 3,000 fatalities from heat stroke.

Reflective roofs and surfaces

In Milos Island, Greece, roofs are painted with white, reflective paint to enhance the albedo effect and reduce local heat. Similarly, Phoenix, Arizona, has applied reflective treatments to surfaces, lowering local temperatures by over 7°C. In Almería, Spain, more than 40,000 hectares of white-topped greenhouses reflect sunlight, cooling the region by 0.3°C per decade, even as nearby areas warm by 0.5 °C per decade.

Expanding green spaces

Green spaces such as urban parks and forests are cooler than paved areas due to evapotranspiration—the process by which plants release water vapour, cooling the air.

Medellín, Colombia, has lowered average temperatures by creating “green corridors” lined with trees along roads, pathways, and cycle lanes. South Korea offers another striking example: in 2005, Seoul demolished a six-kilometre elevated highway to restore a historic stream. The restored green corridor has cooled the neighbourhood by nearly 6°C, while improving biodiversity, reducing pollution, and managing stormwater.

Towards climate-resilient cities

While reflective infrastructure and green spaces are adequate, cities must align cooling strategies with the diverse needs of residents. For example, towns with high pedestrian traffic could combine the widespread use of cool roofs and pavements with tree planting and the creation of shaded areas around commercial zones and transport hubs.

When integrated thoughtfully, these approaches not only reduce the Urban Heat Island effect but also enhance liveability, improve public health, and contribute to climate resilience.

Global cooperation, ensuring companies and governments eliminate deforestation from commodity supply chains (e.g., beef, soy, palm oil).

Cutting fossil fuel emissions, addressing the root driver of climate change. Cooling solutions implemented around the world.