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In Chelsea, cooling an urban heat island one block at a time04:14
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Members of the DCR's Urban and Community Forestry Program plant a cherry tree on Maverick Street in Chelsea, part of the “Chelsea Cool Block” project to help mitigate urban heat in the city. (Jesse Costa/WBUR)
Members of the DCR's Urban and Community Forestry Program plant a cherry tree on Maverick Street in Chelsea, part of the “Chelsea Cool Block” project to help mitigate urban heat in the city. (Jesse Costa/WBUR)

A city block just behind the industrial waterfront in Chelsea is typical for urban heat islands across the U.S. Nearly every foot is covered by a roof or pavement. There’s a Boys & Girls Club at one end and a vacant lot at the other. Ten multi-family buildings with parking lots for backyards fill out the middle. A few weeks ago, there were just five small trees.

But this nondescript slice of the state’s smallest city is worth watching. It may become a template as municipalities struggle with longer, more intense warm seasons and heat waves.

The Cool Block project is loading the area with pretty much every heat fighting tool in use around the country. There are 47 new elm, crabapple, cherry and hawthorn trees. Sidewalks are being ripped up to add planters, porous pavers or white concrete. Dark asphalt will be replaced with gray. There’s a design contest underway for the best way to green and chill the vacant lot. And the city is negotiating with the Boys and Girls Club about installing a white roof.

Arial view of the city block in Chelsea chosen for the Cool Block pilot project. (Screenshot via Google Maps)
Arial view of the city block in Chelsea chosen for the Cool Block pilot project. (Screenshot via Google Maps)

Cooling one city block may not sound like an effective way to tackle climate change, but María Belén Power with the Chelsea-based environmental group Green Roots, says starting small works.

“That has really been an approach that we take in a lot of our projects,” says Power, Green Roots’ associate executive director. “Piloting small scale and ensuring that we can replicate those models to really have a much broader impact.”

State workers and volunteers plant trees on Maverick Street in Chelsea, part of the “Chelsea Cool Block” project to help mitigate urban heat in the city. (Jesse Costa/WBUR)
State workers and volunteers plant trees on Maverick Street in Chelsea, part of the “Chelsea Cool Block” project to help mitigate urban heat in the city. (Jesse Costa/WBUR)

Green Roots is collaborating with the city and researchers at Boston University. The team at BU helped select the block. They started last summer, placing temperature sensors in trees and on roofs around Chelsea.

All 2.5 square miles of the city are considered a heat island. That means residents are at greater risk for asthma and other lung ailments, heart disease and stroke, risks that will only get worse with climate change. But the BU research shows not all blocks pose equal threats. Chelsea has pockets of extreme heat. Temperatures on blocks like this one can be seven degrees hotter than in less sweltering areas of the city.

“It feels oppressive and kind of blinding,” says Madeleine Scammell, an associate professor at the BU School of Public Health. “I’ve walked every street in the city and these are two of the hottest streets.”

Scammell sits at one corner of the block, in front of the Boys & Girls Club.

“We identified the hottest block that we could where there are a lot of people likely to be affected by the heat,” she says.

This map uses temperature sensor data to show pockets of extreme heat in Chelsea. The Cool Block pilot is in the south east pocket. )Courtesy C-Heat Project)
This map uses temperature sensor data to show pockets of extreme heat in Chelsea. The Cool Block pilot is in the south east pocket. (Courtesy C-Heat Project)

Scammell’s team plans to monitor temperature changes during warm seasons for the next few years to measure the impact of the Cool Block pilot. Some residents say the trees are already adding beauty and a sense of well-being, but they’re a long term investment in shade. The white roof and new pavement could help cool the area immediately.

Chelsea’s director of housing and community development, Alex Train, says a white roof on a city elementary school lowered the surface temperature by 20 degrees and the surrounding air temperature dropped by seven to 10 degrees in the summertime.

“The health and environmental benefits are immense,” Train says.

Michael Griffin of the state Department of Conservation & Recreation watches as a volunteer waters the root ball of a cherry tree. (Jesse Costa/WBUR)
Michael Griffin of the state Department of Conservation & Recreation watches as a volunteer waters the root ball of a cherry tree. (Jesse Costa/WBUR)
Brian Martinez, 15, and other volunteers from the neighborhood help remove clay from the root ball of a cherry tree as they prepare to plant it on Maverick Street. (Jesse Costa/WBUR)
Brian Martinez, 15, and other volunteers from the neighborhood help remove clay from the root ball of a cherry tree as they prepare to plant it. (Jesse Costa/WBUR)

The cost of the white roof on the Boys & Girls Club, the road and sidewalk resurfacing, the corner plantings, the trees and the creation of a park in the empty lot will total approximately $350,000. Most of that will come from a state grant.

Other cities are doing pieces of this project. Phoenix pledged to plant 100 tree-lined “cool corridors” by 2030 and is painting streets gray. Philadelphia requires cool roofs, often white, on new construction. Misting projects are opening as a way to cool down residents in Vancouver and New York.

Train says packaging all of these elements on a single block will multiply the impact.

“What we've found is that each of these interventions individually, although they're slightly effective, they're not as effective as they could be if they're implemented in unison,” he said.

Experts offer cautions. Ariane Middel, who studies urban heat impacts at Arizona State University, says it may be difficult to measure which strategies have the biggest impact when they overlap as in the Cool Block pilot. And making some changes on the same street may not make sense. For example, light colored sidewalks are cooler because they reflect sunshine. They aren’t useful under shaded trees.

“Some of the strategies are tough to combine,” Middel says. “You have to think about how to smartly place them and arrange them so they can work together and not against each other.”

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But Middel says it does make sense to start small and focus resources on the hottest areas of a city. Juan Declet-Barreto, with the Union of Concerned Scientists, says low-income areas like Chelsea, where residents don’t always have the means to buy air conditioning or pay a higher electric bill, should be a priority.

“A population of wealthier people that drive air-conditioned cars to air-conditioned offices is not going to need the cooling benefits more than people who ride a bike or walk or take a bus or ride in the back of a pick-up truck to work,” says Declet-Barreto, a senior social scientist for climate vulnerability.

Declet-Barreto says making changes on one block may be easier because there are fewer political hurdles. And the return on dollars spent will be greatest in densely packed neighborhoods, like Chelsea, where the cooling effects will reach more people.

To track the impact of the project, he suggests monitoring 911 calls to see if residents experience any decrease in aggression, mental health problems, heart attacks or any of the other physical ailments linked to heat.

Some residents on or near Chelsea’s “Cool Block” say they are already enjoying the changes. Brian Martinez, 15, volunteered to help plant the new trees.

“Trees do make you calm down,” he says. “And they will give us some shade. We don’t have that now.”

Five-year-old Julia Martinez shovels dirt, as state worker Jake Hennessey assists Malikai DeTar-Kock, 2, and Sonorus Salem, 4, water the root ball of a tree they just set into the ground. (Jesse Costa/WBUR)
Five-year-old Julia Martinez shovels dirt, as state worker Jake Hennessey assists Malikai DeTar-Kock, 2, and Sonorus Salem, 4, water the root ball of a tree they just set into the ground. (Jesse Costa/WBUR)

Green Roots is applying for a grant so it can pay low income residents to water the trees. That’s one lesson learned from past tree plantings that didn’t take root. Many Chelsea residents work two or three jobs. Train says they should be compensated for this additional task.

The Cool Block project may offer additional lessons in the months and years to come. In the meantime, organizers say it gives them hope at a time when climate change updates deliver a lot of doom and gloom.

“Some days we feel like, what are we really having an impact — like is this really going to prevent the climate crisis?” Power asks. “And then I think, ‘It's no longer about preventing it. It's about protecting the most vulnerable communities.’ ”

Editor's Note: Boston University owns WBUR's broadcast license. WBUR is editorially independent.

This segment aired on May 12, 2022.

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Martha Bebinger covers health care and other general assignments for WBUR.

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