Reflective Pavements: A Smart Solution to Cool Cities When Used Strategically

As heat waves become more frequent, cities are exploring various methods to reduce temperatures, and one promising solution lies right beneath our feet: pavement. Dark pavements and asphalt absorb heat, raising not only their own temperature but also the surrounding air temperature, exacerbating the urban heat island effect.

The Science Behind Surface Heat

Urban areas are particularly prone to heat retention due to the large amount of paved surfaces. Approximately 40% of urban land is covered in pavement, which absorbs solar radiation during the day and releases it slowly, keeping the environment warm even after sunset. This contributes to cities being several degrees warmer than nearby rural or suburban areas.

How Reflective Pavements Work

Reflective pavements counteract this heat retention by increasing the surface’s albedo, which is a measure of how much light a surface reflects. Dark surfaces, like conventional asphalt, have a low albedo of 0.05-0.1, meaning they absorb up to 95% of the sunlight they receive. By using lighter-colored materials, reflective aggregates, or special coatings, the albedo can be tripled, reflecting more solar radiation back into the atmosphere and reducing the heat absorbed by the pavement.

The Benefits of Reflective Pavements

Research from MIT’s Concrete Sustainability Hub (CSHub) has shown that increasing the albedo of pavements can significantly reduce air temperatures and greenhouse gas emissions. A model from MIT CSHub estimated that enhancing the albedo across all U.S. roads could decrease energy use for cooling and cut greenhouse gas emissions equivalent to taking 4 million cars off the road for a year. Additionally, using locally sourced materials for these pavements can save costs.

Strategic Placement is Crucial

However, the effectiveness of reflective pavements varies depending on their location. In some areas, reflective surfaces can inadvertently increase the heat load on nearby buildings, raising air conditioning demands. Therefore, strategic placement is essential.

Case Studies: Boston and Phoenix

In Boston, reflective pavements could be beneficial on unobstructed freeways and suburban roads, potentially lowering peak summer temperatures by 1 to 2.7 F (0.3 to 1.7 C). However, in Boston’s dense downtown with narrow streets and tall buildings, the benefits are minimal.

Phoenix, on the other hand, could see a temperature reduction of 2.5 to 3.6 F (1.4 to 2.1 C) with reflective pavements. But in some low-density downtown areas, increased incident radiation on buildings could actually raise cooling demands.

Lessons from Los Angeles

Los Angeles has experimented with cool coatings over asphalt. While these coatings reduced ground temperatures by up to 11 F (6.1 C), they increased temperatures slightly above the ground due to reflected sunlight. This suggests that such coatings might be more effective on roads rather than sidewalks or playgrounds.

The Way Forward

Reflective pavements offer an elegant solution to urban heating, but their implementation must be carefully planned. Cities need to consider the lifecycle emissions of the materials used, the specific urban layout, and the potential unintended consequences of increased reflective radiation.

Strategically optimizing pavement albedo can make urban areas more livable and contribute significantly to mitigating climate change effects. By transforming everyday surfaces into tools for cooling cities, we can take a significant step towards sustainable urban living.

source :

https://www.preventionweb.net/news/lighter-pavement-really-does-cool-cities-when-its-done-right