With the hot July sun beating down, Josh Kumin headed south on 13th Street, heat sensor in hand.

He stopped, just past the Boulder Museum of Contemporary Art, and took his first reading: 102.8 degrees.

Kumin was one of more than 100 people who participated in a one-day study to learn more about where extreme heat poses the greatest risk in Boulder. The city, which conducted the study in partnership with the National Oceanic and Atmospheric Association, is one of 18 across the country participating this year in the urban heat mapping initiative.

The effort was conducted Friday, which organizers determined to be one of the hottest days of the year as well as a dry day with little to no cloud coverage.

Some volunteers drove in their cars, collecting data with high-resolution sensors mounted to record the temperature every second as long as the vehicle is going 35 miles per hour or slower.

Others, including Kumin, walked or rode their bikes to collect data.

“I didn’t even realize these tools were even available to capture this data. It’s really interesting,” he said. “I think I’ve just typically thought of temperature as being pretty constant in the area.”

The fact that temperature can be different in one area, depending on what’s growing naturally and what buildings and structures are there, is something Kumin said he’d never really considered.

But conversations with Adam Hall changed that.

Hall, a graduate student at the University of Colorado Boulder, helped coordinate Friday’s study as part of a university capstone project.

“I always knew urban heat is an issue; just growing up in a city and experiencing how much hotter our cities are compared to the area just outside,” he said.

“Thinking spatially about environmental hazards is something I really enjoy,” Hall added.

Generally speaking, he is expecting areas with impervious surfaces such as concrete or asphalt to be much hotter than those with grass or water. The data is also certain to influence Boulder’s urban forest expansion goal, allowing the city to target planting trees in areas with the highest heat.

The more official data that can be replicated is being collected by those in cars, Natural Climate Solutions Policy Advisor Brett KenCairn acknowledged.

But those traversing the streets by bike and foot had an important role, too, he noted.

“The other approach that we’ve created is more of an experiential opportunity for people, but we think that it has some potential down the road for being a way that we can do some simple citizen science year over year to watch these numbers,” KenCairn said.

It’s also a good way for older adults and children to participate, he said.

The study is part of the newly launched Cool Boulder campaign, which looks to expand natural climate solutions in order to impact the more stringent set of climate targets the Boulder City Council adopted in 2021.

The campaign includes three action areas: pollinator pathways, connected canopies and absorbent landscapes. These efforts will help cool temperatures, foster biodiversity and hold more carbon, water and thermal energy within particular landscapes.

In addition to providing the city with information that can improve its climate readiness, Boulder will provide the data collected Friday to NASA’s Jet Propulsion Laboratory so it can be used to help create new heat models for the Earth.

Boulder climate team, volunteers look to better understand urban heat