Taking the actual temperature of Twin Cities area neighborhoods

The last Saturday in July brought a heatwave to the Twin Cities, with temperatures hovering above 90 degrees. But it felt much cooler on a shady block in south Minneapolis’ Kingfield neighborhood.

The leafy stretch on Pillsbury Avenue was where Anna Berglund and Seiko Shastri started collecting data to help Hennepin County officials understand which areas of the city are hotter than others, and the differences between blocks.

Berglund and Shastri were among more than 120 volunteers who spent July 27 driving across the Twin Cities using window-mounted sensors to collect street-level data on the urban heat island effect. As the temperature gauge in their Evie Carshare Nissan Leaf hovered in the low 90s, they drove through forested parkland near Lake Nokomis and past industrial parks off Hiawatha Avenue.

“This is the perfect day to do this,” Shastri said.

The National Oceanic and Atmospheric Administration (NOAA) selected Hennepin and Ramsey counties to participate in its urban heat island mapping project, which has studied the heat island effect in cities around the world for the past eight years. Urban areas experiencing a heat island effect can have a temperature difference of up to a 20 degrees, depending on the amount of shade.

Shadier sections, typically in predominantly white neighborhoods, are cooled by tree cover, while areas dominated by asphalt, concrete and industrial parks are more exposed to the sun. A 2020 study revealed that Minneapolis’ formerly redlined neighborhoods, areas where discriminatory housing practices took place from the 1930s through 1960s, were almost 11 degrees hotter than the city’s coolest neighborhoods.

The data will be used by the two counties to allocate climate investments aimed at reducing the disparities between wealthier, whiter neighborhoods and formerly redlined areas that are home to more immigrants and people of color.

“We see a strong correlation between areas that are hotter and areas that are formerly redlined,” said Cliff Mountjoy-Venning, a senior planning analyst on Hennepin County’s climate and resilience team.

The two counties submitted a joint application for the NOAA project, with support from the University of Minnesota and the cities of Minneapolis and St. Paul. The project has financial backing from the U.S. Health and Human Services and Housing and Urban Development departments.

The project typically selects individual cities, but climate staffers at Hennepin and Ramsey counties decided they would have a better chance with a joint application. Officials in both counties say reducing the urban heat island effect is one of the racial equity goals baked into their respective climate plans.

Areas that are socially and economically vulnerable in Ramsey County feel hotter in the summer, according to climate and health supervisor Abigail Phillips. “It’s an unfortunate pattern,” she said.

Using satellite imaging, the Metropolitan Council mapped the urban heat island effect across the seven-county metro area in 2016 and 2022. The NOAA project uses sensors from CAPA Strategies, a company that analyzes the data for the federal government; past studies are available online at Heat.gov. Data collected in Hennepin and Ramsey counties is expected to be available this fall.

“It’s going to have similar trends, but it’s going to be a little more targeted and focused,” Mountjoy-Venning said.

Heat islands in the Twin Cities are concentrated in the downtowns of Minneapolis and St. Paul, along major highways, and in industrialized areas such as St. Paul’s Midway. Hotter environments are linked to cardiovascular and respiratory issues, and heat waves can be deadly for the very young or old, pregnant women and people who work outdoors.

Ramsey County sent data collectors across all 152 square miles, Phillips said, with an emphasis on areas deemed socially vulnerable and points of interest such as schools, libraries and light-rail stations.

Much of Hennepin County’s 554 square miles is farmland or leafy suburbia, so county officials decided on a mix of routes that emphasized the urban core: north Minneapolis and the northwest suburbs, northeast Minneapolis and Fridley, south Minneapolis, Edina, Richfield and Bloomington.

“Heat doesn’t stop at city borders, so we want to make sure we’re providing this information for as much of the county as we can,” Mountjoy-Venning said.

Officials said they were impressed by the number of volunteers willing to devote a summer Saturday to data collection. After virtual training, volunteers had their vehicles outfitted with sensors just after dawn on the collection day. They were instructed to stick to their routes and stay under 35 mph to ensure the sensors could take an accurate temperature reading every second.

The volunteers drove their routes three times to capture the heat island effect across the day — early in the morning, in the heat of midafternoon and in the evening. Berglund and Shastri diligently drove their route and made time notes in a message to administrators when they briefly made a wrong turn. Those notes are important to the integrity of the data collected, according to Phillips, and a reason that both counties were so impressed with their volunteers.

Berglund and Shastri said they were excited to see the data when it comes out, and hope it results in tangible benefits for residents. “I think it’s cool,” Shastri said. “It’s a fun, sort of unusual engagement opportunity.”

About the partnership

This story comes to you from Sahan Journal, a nonprofit newsroom dedicated to covering Minnesota’s immigrants and communities of color. Sign up for a free newsletter to receive Sahan’s stories in your inbox.