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Volunteer Pat Meyers attaches a heat sensor to the window of Deborah Rylander’s car to collect data on heat and humidity on July 22, 2022. The one-day study was conducted by the city of Boulder and the National Oceanic and Atmospheric Association, or NOAA. 18 cities nationwide participated in the heat mapping project. (Olivia Sun, The Colorado Sun via Report for America)

A volunteer-led project to identify the hottest and coolest parts of Boulder shows cooling stations and other solutions are most needed in the city’s commercial corridors — where multiple lanes of road and big parking lots absorb and hold heat — and in low-income neighborhoods, where there are few trees and homes aren’t air conditioned.

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The project also delivered data that helps city leaders plan for the extreme heat scientists have warned about for years.

“We’re going to take into consideration, both where it’s hot, and where people are most vulnerable. And those are the areas that we are going to be targeting,” said Brett KenCairn, the city’s natural climate solutions team leader for the project. 

More than 70 volunteers fanned out across the city on July 22, one of the hottest days this summer, in the annual heat-mapping project. The results were released Friday.

The most consistently warm areas were in the 28th Street commercial corridor from Iris Avenue south to Baseline, and in downtown, the samples show. The temperatures in those areas were consistently 10 degrees warmer than in other parts of the city, KenCairn said.

Some of the hottest areas recorded that morning were along 28th Street and in West Boulder, near the Foothills. But during the afternoon, when the hottest overall temperatures were recorded, west Boulder became one of the coolest areas in the city likely because of topography, sun exposure, location and elevation, he said. 

Some of the coolest areas were recorded that morning near the Martin Acres neighborhood on the south side of town, and in some parks in East Boulder, he added. 

Downtown Boulder and other largely commercial areas will now be targeted for heat-reduction activities, KenCairn said, such as by increasing tree planting to reduce heat. But more importantly, lower-income neighborhoods, and places with fewer trees, will be targeted for solutions such as by enhancing people’s access to cooling centers, low cost air conditioning, electric heat pumps and possibly evaporative coolers, KenCairn said.

Volunteer Pat Meyers attaches a heat sensor to the window of Deborah Rylander’s car to collect data on heat and humidity on July 22. The one-day study was conducted by the city of Boulder and the National Oceanic and Atmospheric Association, or NOAA. 18 cities nationwide participated in the heat mapping project. (Olivia Sun, The Colorado Sun via Report for America)

City leaders will not only consider the hottest spots in Boulder for heat-reduction solutions. They’ll also consider the most vulnerable areas in the city for heat-reduction activities, such as the intersection of social vulnerability or residents’ access to resources like air conditioning and people’s physical condition. The work will take years to complete, KenCairn said.

“Thinking about this in the context of where people live and work and where they play and how heat affects them throughout their daily routine is one of the big things we want to highlight,” said Adam Hall, a graduate student at the University of Colorado studying urban resilience and sustainability, who is helping to lead the local initiative.

The key findings also showed:

  • Areas with little vegetation and a high proportion of impervious surfaces, such as roads and parking areas, were significantly hotter. In some cases, these areas were 17 degrees hotter, one of the greatest heat ranges of all cities that participated in the one-day national study.
  • Trees played a big role in keeping Boulder’s neighborhoods cool. Residential areas with lots of tree coverage seemed to hold less heat throughout the day and densely vegetated areas, like those along Boulder Creek, cooled adjacent neighborhoods.
  • There were significant differences in tree canopy, or the parts of the city that are shaded by trees, resulting in higher risks of extreme heat exposure in some areas with massive parking lots and tiny trees, such as along 28th Street or in downtown Boulder. Now, additional work is underway to assess how these areas are linked to other heat-related risks, such as lack of access to air conditioning. 

Half of Boulder’s housing stock does not have air conditioning, “because we didn’t used to need air conditioning in Boulder,” KenCairn said. “That’s why people came here for the summers.”

The findings will now help guide strategies that reduce the unhealthy and deadly effects of extreme heat, study leaders said, including nature-based solutions that enhance shade and evaporative cooling, like expanding urban forests, and increasing access to high-efficiency cooling systems for people most vulnerable to heat extremes.

“This data also illustrates the importance of a diverse, healthy and resilient urban landscape as we work to cool and protect our community,” KenCairn said.

In late July, volunteers fanned out across seven predetermined routes across Boulder on car, bike and foot as they used heat sensors to record the time, temperature and humidity to help scientists tracking climate trends nationwide. The routes included some of the most low-income and environmentally vulnerable parts of wealthy Boulder. 

The study was conducted by the city of Boulder and the National Oceanic and Atmospheric Administration, or NOAA, and CAPA Strategies, a climate planning and analysis consulting firm.

Eighteen cities participated in the nationwide project this summer, collecting heat data in Nevada, South Carolina, Ohio, Philadelphia, New York and San Francisco, among others. NOAA is also working with local groups on heat-mapping campaigns internationally in Freetown, Sierra Leone and Rio de Janeiro.

As climate change increases temperatures across the globe, the most vulnerable communities are facing the greatest heat burden, according to study leaders

Extreme heat kills more Americans than any other weather event but not everyone’s risk is the same. Extreme heat most adversely affects older adults, low-income communities, people of color, people with preexisting health issues, infants, outdoor workers and residents without access to air conditioning.

Dense urban areas with many dark surfaces that absorb and hold heat, such as parking lots and roads, make urban areas hotter than rural or suburban ones.

The summer study collected data in three shifts throughout the day. During the morning shift, the valley of Boulder, recorded at the lowest temperature of 61 degrees, and at the same time of day, another area, the western foothills, recorded at 78 degrees, the greatest range in temperature that NOAA collected across all cities this year. 

Sun exposure majorly contributes to the difference in temperature, because the mountains have a strong influence on the shading of the entire community, KenCairn said. 

Location also is a factor. In areas with little vegetation and almost all impervious surfaces like those near downtown Boulder, where there’s lots of concrete and asphalt, there’s no way for these surfaces to cool down and they instead re-radiate heat, he said.

The change also partly occurred because of Boulder’s unique topography at the base of the foothills, at an elevation of 5,430 feet. Elevation is a small factor that influences temperature. Temperature tends to drop as elevation rises.

Now that the hottest areas of Boulder are mapped, study leaders said, the city and its climate partner organizations can identify natural climate solutions. 

The Cool Boulder campaign, a long-term effort to create partnerships to implement natural climate solutions, is working with the city and other organizations to use tree planting, pollinator gardens and conservation of natural areas that absorb carbon, moisture and energy to mitigate the effects of climate change and extreme heat. 

Boulder leaders are now calling on members of the public to help implement some of these solutions. To get involved, visit:

Tatiana FlowersEquity and general assignment reporter

Tatiana Flowers is the equity and general assignment reporter for the Colorado Sun. She has covered crime and courts plus education and health in Colorado, Connecticut, Israel and Morocco. In her spare time, she enjoys skiing, intense exercise, working as a local DJ, and live music...