Asphalt, concrete, and lack of tree cover raise city temperatures. Roads, rooftops, and other surfaces retain ultraviolet rays emitted by the sun and emit heat throughout the day and even at night.
This trapped heat creates urban heat islands, areas where natural ground cover is replaced by pavements, buildings, and other surfaces that collect more heat than other areas.
Smart surface technologies* can help mitigate the effects of the climate crisis by lowering urban temperatures.
Smart surfaces are coming to streets, parking lots, and rooftops in the United States and soon to the rest of the world.
What are smart surfaces?
According to the Smart Surfaces Coalition, a group of 40 national and international organizations working to make urban centers more climate-resilient, smart surfaces are technologies that mitigate the rise in temperatures caused by the climate crisis, enhancing urban resilience and saving money.
They include:
• Reflective coatings on roads.
• Outdoor shade structures with solar panels.
• Cool roofs that reflect heat from buildings.
• Green roofs and vegetation-covered walls.
• Porous pavements that absorb rainwater and recharge aquifers.
When extreme heat and urban heat islands meet, it becomes nearly impossible for regions of cities to reach lower temperatures at night, leading to a buildup of heat during the day.
Smart surfaces can help lower temperatures at night. Roads absorb heat during sunny hours; therefore, if reflective surfaces absorb less heat during the day, the roads will not retain and radiate heat at night.
“Since black asphalt absorbs 95% of heat, urban heat islands are felt at night, and that’s when they are slowly releasing heat,” said Davis Koleas, Sustainability Director at CoolSeal by GuardTop, a company that manufactures smart surfaces. “But cool pavements reflect 35% to 40% of solar heat.”
Two different analyses from 2021 — one in Stockton, California* and another in Baltimore* — demonstrated that “citywide adoption of 12 smart surface strategies over 20 years would reduce peak summer temperatures by nearly 3 degrees Celsius, reduce the city’s carbon dioxide emissions by over 10%, and have a cost-benefit ratio of over 5 to 1,” said Jackson Becce of the Smart Surfaces Coalition.
He mentions that a similar analysis is underway* in Bhopal, India, aiming to test the effectiveness of smart surfaces.
A recent pilot program by Arizona State University and the Streets Transportation Department along with the Office of Sustainability, both from the city of Phoenix, found that reflective road coatings can reduce road surface temperatures by around -12° to -9° Celsius. The coatings can also lower ambient air temperature, but this is harder to measure.
“We had great results,” said Ryan Stevens, Engineering Manager for the city of Phoenix who was involved in planning the citywide Cool Roads Partnership. “Even small temperature reductions combined across an entire urban area can result in a really positive impact.”
Smart surfaces are a technique that can help mitigate the negative effects of the climate crisis. Others include greening measures, such as increasing tree canopy, urban farms, and public gardens.