Cool Pavements Show Promise as Part of Urban Climate Resilience Strategy

Dr. Haider Taha is President and Scientist at Altostratus Inc., a California-certified small business specializing in regional to urban atmospheric and environmental modeling and research.

Our greatest threat: extreme heat 

2023 was the fifth-warmest year on record for the United States, and it’s estimated that 65 million people across the country were impacted by heat last year. What’s more, 35 states, or more than half of the nation, experienced a top-10 warmest year in 2023 for the state. 

During July 2023, the hottest month recorded on Earth, one in five Americans reported experiencing temperatures of at least 100 degrees Fahrenheit in their area, and more than half (52 percent) experienced temperatures of at least 90 degrees Fahrenheit. Because of these extreme temperatures, many people experienced health issues, with more than one in five reporting dehydration, heat exhaustion, and rashes.

As temperatures rise to high and harmful levels, human health and overall livability are negatively affected, especially for people residing in urban areas. Today, nearly 80 percent of the U.S. population lives in cities, where the urban heat island effect can worsen heat extremes because of dense concentrations of pavement, buildings, and other surfaces that absorb and retain heat and a lack of trees and vegetation. When our cities become too hot, people and the planet suffer.

What is the solution to tackling extreme heat and alleviating the urban heat island effect? There is no silver bullet, but there are several actionable solutions. Cities and municipalities across the country have assessed and implemented innovative technologies and strategies to combat the growing threat of extreme heat.

A unique approach to fighting extreme heat 

The GAF Cool Community Project was a one-of-a-kind, community-wide research initiative spearheaded by GAF, the largest roofing and waterproofing manufacturer in North America, to assess and understand the impacts various cooling solutions have on urban heat and livability. Through this effort, which is a part of the company’s broader social impact initiative Community Matters, GAF worked with local organizations Climate Resolve and Pacoima Beautiful, as well as Altostratus and the City of Los Angeles, to install cool pavements in the Pacoima neighborhood.

The multi-phase project was launched in July 2022 in Pacoima, California, one of the hottest neighborhoods in Los Angeles, which historically has been underinvested in when it comes to climate solutions. What’s more, a majority of the 85,000 residents who call Pacoima home have spent much of their time inside in the past few summers because of the extreme heat, limiting their exposure to community engagement and overall livability.

In July 2022, the community coalition spearheading the project applied GAF Roads’s DuraShield-SR, a solar-reflective pavement coating, to more than 700,000 square feet of neighborhood streets and GAF StreetBond SR coatings to basketball courts, parking lots, a school playground, and a colorful community mural by a local artist. This was the largest contiguous application of cool pavement coatings known to date. Uniquely, the project involved a robust community engagement process to drive local involvement in the effort, measure qualitative and quantitative impact on how community cooling improves livability throughout the neighborhood, and ensure the success of the project.

Over the course of the next 12 months, scientists at Altostratus monitored community cooling in the neighborhood and collected observational data from 73 high-resolution mobile transects to examine and identify the impact of the cool pavement treatment. The project team deployed weather stations and a mobile platform to measure various indicators such as air temperature, humidity, incoming and reflected solar radiation, precipitation, wind speed and direction, atmospheric pressure, vapor pressure, lightning, and wind gusts to characterize conditions before and after the reflective coatings were installed. Satellite, aircraft, and drone instruments were also utilized to conduct additional remote-sensing measurements.

The results are in, reviewed — and impactful

In April 2024, the research findings were peer-reviewed and published in the IOP Environmental Research Communications journal. The study revealed reductions in ambient air temperatures by as much as 3.5°F during extreme heat events and a 25-50 percent reduction in the local census-tract urban heat island index during daytime temperature peaks. The research also indicated notable reductions of up to 10°F or more in surface temperatures following the application of GAF solar reflective, or “cool,” pavement coatings, which directly correlated to a reduction in air temperature and felt temperature in the community. The application also resulted in radiant temperature (e.g., MRT), which quantifies the exchange of radiant heat between a human and their surrounding environment, influencing personal comfort, experiencing a reduction of around 1.5 °F. Other thermal-comfort indicators used in the study also showed net reductions in heat effects.

In addition, using the project’s weather stations and a mobile platform to measure various indicators along with satellite, aircraft, and drone instruments, the study also found that through typical and hot-weather summer conditions, the effects of cool pavements were beneficial — the coatings contributed to lower temperatures in the areas with coated streets and slower warming before noon as well as faster cooling after noon time in some instances. Some of the larger reductions in temperature from the cool pavement coating were observed during a heat-wave event, which was an instance when the coatings were most effective.

What do these findings mean to community members? In simple terms, it means it feels less hot outside for them. Several Pacoima residents reported feeling cooler in their neighborhood and said more children are spending more time outside on the playground and playing on the local basketball courts again. Some community members have also asked for more pavements to be applied in their neighborhood because of the positive benefits they’ve experienced. One Pacoima resident, Jeniffer Ramirez, said, “The project you all have brought to us, has been a life changer. I have seen a lot more people out now than there have ever been.”

What’s more, the pavements also had aesthetic benefits for the neighborhood. Available in a wide range of colors, these solar-reflective coatings enable communities to turn pavement into works of art, making spaces beautiful and safe while mitigating extreme heat. In Pacoima, the vibrant StreetBond color palette was used for the community mural, basketball court, school playground, and crosswalk to the park.

While the initiative and study are finished, the work isn’t done. The Community Matters initiative plans to introduce cool roofing technologies in Pacoima and learn more about their cooling benefits for homes and homeowners.

The future of cool pavements

Combating extreme heat and fostering resilience in our communities will require a toolbox of solutions. The GAF Cool Community Project and this study by Altostratus demonstrated that cool pavements are an effective strategy to mitigate urban heat and provide positive environmental and social benefits to communities and residents. Cool pavement and cool roofing technology are tools every municipality can incorporate into their infrastructure, roads, and building plans and repairs to improve, enhance, and protect livability for people and communities.