In Boston’s heat islands, summers are becoming unbearable
It was so hot that day, the whole week for that matter, that Zaida Rodriguez swears she could see the heat radiating off of the pavement.
Boston was in its second heat wave of summer 2021, and Rodriguez, 23, could find little refuge from the swelter in Lower Roxbury, the community she’s lived in since she was a child.
The sidewalks — in most places barren patches of concrete with little, if any, shade — became unbearable after even 30 seconds outside. So Rodriguez spent the afternoon in her apartment, crouched in front of an oscillating fan and holding an ice pack to her neck and face.
“I could barely think, that’s how f— hot it was,” Rodriguez said, recalling the day with a grimace.
Not half a mile away, in neighboring Jamaica Plain, the feeling was different. Hot, yes. But residents spent the afternoon walking the tree-lined trails around Jamaica Pond and perusing the sprawling Arnold Arboretum. Data from the National Oceanic and Atmospheric Administration indicates that, at the hottest point that day, June 29, the difference in temperature between the two neighborhoods was a whopping eight degrees.
The disparity highlights a vexing reality for Boston residents: the city is getting hotter, and lower income neighborhoods left behind by historical disinvestment are bearing the brunt thanks to the so-called urban heat island effect.
That phenomenon — occurring in regions with an abundance of concrete and asphalt, which absorb sunlight and amplify the temperature on hot days — is well-documented. So too are the health consequences of extreme heat. Less prolific, though, are potential solutions, any of which will inevitably prove an immense infrastructure challenge for an aging city.
On Earth Day last week, Mayor Michelle Wu announced a series of steps the city will take towards combating heat inequities, chief among them a goal to expand tree cover for neighborhoods in desperate need of shade.
It was perhaps the first urgent action Boston officials have taken against oppressive heat in the city. More can’t come soon enough, experts said.
“Growing up it wasn’t like this,” said Rodriguez. “Now we can’t even let our kids out of the house some days. It's dangerous. I can’t imagine it any hotter than last summer.”
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The streets in Roxbury, East Boston, and Chinatown, some of the city’s most intense heat islands, are dense. Buildings are packed close together. And a key ingredient for magnified heat abounds — pavement.
Hessam Azarijafari, a researcher in the Massachusetts Institute of Technology’s Concrete Sustainability Hub, said it is these sorts of neighborhoods, where the trees and parks are few and the buildings are many, that are most susceptible to extreme temperatures. Not only do they get hotter faster and reach temperatures higher than most other neighborhoods, they also take much longer to cool down.
“These materials absorb a lot of heat and this heat will remain… [until] the nighttime when the temperature decreases,” said Azarijafari. “As a result of this temperature decrease, the amount of heat absorbed will be released to the atmosphere and make the surrounding neighborhood warmer.”
The heat in Boston last summer was oppressive in every corner of the city. Between June and August, four sustained heat waves, three or more days with temperatures exceeding 90 degrees, descended on the city, according to NOAA. In total, there were 24 days when temperatures hit 90 degrees or higher, the sixth most ever recorded in Boston. It was the hottest June on record. And the average temperature from June through August, 74.5 degrees, was the highest it's ever been, according to NOAA data.
It was a glimpse into the future.
By the end of the decade, the city projects temperatures to exceed 90 degrees for over 40 days a year. By 2070, that number could be as high as 90 days a year, a dramatic escalation from the 11 day average mark recorded in 1990.
That means temperature disparities will only worsen, though they are already on full display.
Take 2019, when a team of researchers fanned out across Boston’s census tracts for two days and recorded temperatures at 6 a.m., 3 p.m., and 7 p.m. The resulting data paints a picture of a city whose most vulnerable residents face some of its most intense heat.
For example, on the days the data was collected, the census tract encompassing East Boston’s Eagle Hill neighborhood registered an afternoon high temperature of 97.38, while tracts in wealthier, whiter Jamaica Plain all registered around 95 degrees. At 7 p.m., the Eagle Hill area still registered around 91.5 degrees. The temperature in Jamaica Plain had dipped to between 86 and 87 degrees.
Boston high temperatures at 3 p.m. in July 2019. Link.
Those disparities are inextricably linked to discriminatory policies of old, research has found.
Inequities in the city’s heat can be traced back as far as the early 1900s, when banks, at the behest of the government, engaged in redlining, or labeling neighborhoods with large populations of Black and brown families as “hazardous” to investors. The result was decades of disinvestment in redlined neighborhoods like Roxbury and Dorchester that prevented generations of people of color from accumulating wealth through property. Those communities never saw the beautification efforts that brought grassy parks and rows of trees to neighborhoods like the Back Bay.
“Along with all of the other ways redlining did harm to people of color, what it really did that a lot of people don’t think about is it kept trees out of those neighborhoods that were designated as ‘hazardous,’” said David Meshoulam, executive director of Speak for the Trees Boston, a nonprofit group that organizes around what it calls “tree equity.”
Boston high temperatures (July 2019) in relation to tree canopy. Link.
Trees, Meshoulam explained, play a big role in affecting the heat dynamics of a neighborhood. Heat islands lack trees, he said. Inversely, neighborhoods with a high percentage of tree canopy, or leafy cover measured via satellite imaging, don’t get as hot, and they cool off far quicker because they are better shielded from the sun.
Overall, Boston’s tree canopy stands at roughly 26 percent, but much of its coverage is concentrated in parks and wealthier neighborhoods, according to city data. A census tract bordering Franklin Park in Jamaica Plain, for example, is 87 percent covered by the canopy. A census tract in Chinatown, meanwhile, is only roughly 5.5 percent covered, the data indicates.
Boston mean afternoon high temperatures July 2019 in relation to tree canopy. Link.
Indeed, the tree canopy in areas of Boston that were redlined fall short of the canopy in those that weren’t. In the report published by the city last week, researchers concluded that during a heat wave, redlined areas can be 7.5 degrees hotter in the day and 3.6 degrees hotter at night than the rest of Boston. Those areas have roughly 20 percent less parkland and 40 percent less tree canopy than neighborhoods that weren’t redlined.
Extreme heat also leaves underprivileged communities at increased risk of heat-related health complications. It raises mortality and morbidity rates, and risk of heat stroke, exhaustion, and respiratory issues, according to the Centers for Disease Control and Prevention.
Comparing income level, people of color, and heat in Boston. Link.
The solutions are of much debate.
For its part, the city has committed to revitalizing Boston’s urban canopy, which, if done properly, would certainly help reduce extreme heat in the city, experts said.
“Trees are absolutely a way out of this problem,” said Meshoulam. “But trees are also expensive, they are picky, they are needy, and they take their time. If you plant trees now, depending on the [species], you may not have a full grown tree for 10 years.”
But logistical hurdles abound. On their own, trees can be expensive to plant, Meshoulam said. Perhaps the biggest challenge, though, will be the city’s existing infrastructure. As it is, very little space is available to plant trees in the areas that need them the most. Chinatown, for example, has almost no “possible tree canopy space” according to the city’s data. To plant in those neighborhoods would mean tearing up sidewalks, navigating zoning codes, and hiring new teams to care for the trees as they grow.
“Implementing urban vegetation is very effective but to gain the benefits it takes a lot of time,” said Azarijafari, the MIT researcher. “If you plant a tree, [you] have to have a fast growing tree that can provide enough shade to mitigate the urban heat island effect. It also has limited scope of application because we know that in many parts of the city, roads are already built [so] it's really hard to expand the urban vegetation or grasslands.”
Boston afternoon high temperature, overlaid with potential space for canopy expansion. Link.
To supplement what may be slow-going tree planting efforts, Azarijafari said the city should explore alternatives like “cool pavements,” a reflective coating painted on road surfaces that acts to reflect heat, rather than absorb it. There would be regular maintenance costs (the pavements have to be reapplied once yearly, as wear and tear from tires causes the reflectivity of the material to decline dramatically), but some cities, like Phoenix, Arizona, have used them with some success.
Some studies, though, like one conducted on cool pavements in use in Los Angeles, suggest the material’s reflective quality may have an unintended consequence. That particular study found the reflective materials led pedestrians to experience temperatures around seven degrees higher than normal in the afternoon.
In her Earth day remarks, Wu said the city would also look to implement so-called “green roofs,” a “vegetative layer grown on a rooftop,” as the Environmental Protection Agency puts it. These urban gardens provide shade, removing heat from the air and reducing the temperature on the surface of the roof and in the air. The EPA says the roofs can reduce citywide air temperatures by up to 5 degrees if used in high enough quantities.
The city has also said it will implement “white roofs,” which reflect radiation, and solar roofs, which generate renewable energy and provide shade.
Whatever the solution, some residents say it can’t come soon enough.
Elena Costa, 43, has lived in East Boston’s Eagle Hill neighborhood for more than 30 years. Last summer, the heat was so unbearable and unrelenting that she almost considered moving.
“It’s hard to live, to function when it’s that hot,” said Costa. “I can’t even go to the grocery store down the street. I feel like I’m going to pass out. I am hoping this summer is better.”
To see our methodology and datasets, click here.