Part 4: You will hear a lecturer talking about Urban Albedo Coatings.
Lecturer: Today I’m going to talk about a simple approach that some cities are using to reduce extreme heat. It is called urban albedo coatings. The idea is easy to understand. Many surfaces in cities are dark, especially roofs, roads, and car parks. Dark surfaces absorb more heat from the sun. They warm up quickly during the day, and they stay warm for a long time afterwards. This is one reason city temperatures can be higher than nearby rural areas, particularly in summer and during heatwaves.
So, what does albedo mean. Albedo is a measure of how much light a surface reflects. A high albedo surface reflects a lot of sunlight. A low albedo surface absorbs more. If you look at a white surface on a sunny day, you can see how bright it is. That brightness is related to reflectivity. Urban albedo coatings are thin layers that are added to an existing surface to increase reflectivity. In simple terms, they help a roof or a road reflect more sunlight and absorb less heat.
Let’s talk about where these coatings are used. The most common place is on flat roofs, especially on large commercial buildings like warehouses, shopping centres, and office blocks. There are a few reasons for this. Roofs are directly exposed to the sun for many hours, and they cover a large area. If you can keep a roof cooler, you can often reduce heat inside the building as well. Coatings can also be used on roads and pavements, but that depends on the local situation, because roads need materials that can handle heavy traffic. In some cases, coatings are also used on building walls, although that is less common. Walls can be more visible to the public, and people sometimes have concerns about appearance.
Now, what effects do these coatings have. When a roof reflects more sunlight, the roof surface temperature can drop, sometimes by a large amount on a hot day. That can reduce indoor temperature in rooms just below the roof. The biggest benefit is often seen on the top floor, where the heat from the roof would normally enter the building. If the indoor temperature is lower, people use less air conditioning. That can reduce electricity demand, especially in the afternoon when cooling systems are working hardest. In some cities, cutting peak demand is a major reason for supporting these coatings, because power systems can struggle during heatwaves.
There can also be wider benefits at the city level. If many buildings in a district use reflective roofs, the overall heat stored in the city can be reduced. That may help lower surface temperatures across a wider area. The change is not the same everywhere, and it depends on building density, weather, and local wind, but the goal is to reduce the intensity of urban heat. People may feel more comfortable outdoors if pavements and surrounding surfaces are cooler, because there is less heat radiating from the ground and buildings.
However, there are practical issues, and it is important to be clear about them. The first issue is maintenance. These coatings work best when they are clean. In real cities, surfaces collect dust over time. Dust reduces reflectivity. When the coating becomes dirty, it reflects less sunlight, so its performance drops. Some cities schedule cleaning or re-coating, but that adds cost and needs planning.
Another issue is glare. If a surface becomes very reflective, bright light can be uncomfortable for people nearby. Glare can affect drivers, pedestrians, and people in buildings that face the coated surface. Because of this, designers sometimes choose materials that are reflective but not highly glossy, and they may avoid certain locations where glare would be a serious problem.
So, to sum up, urban albedo coatings are a straightforward way to reduce heat absorption in cities. They are thin layers applied to surfaces, most often roofs, to reflect sunlight. They can help reduce indoor temperature, lower electricity demand for cooling, and in some cases reduce surface temperatures in the wider urban environment. But they need maintenance because dust reduces effectiveness, and planners have to consider glare. In the next part of the lecture, I’ll look at how cities decide where to use these coatings and how they measure the results.
