‘Linear urban forest’ project aims to mitigate heat, improve health in cities

Linda Powers Tomasso presents plan for "linear urban forest" to Springfield residents
Linda Powers Tomasso presents plan for "linear urban forest" to Springfield residents

June 28, 2024 – In mid-May, a group of Springfield, Mass. residents gathered in a downtown meeting room to view, on a big screen, computer-generated visualizations of what streets in the Upper Hill neighborhood would look like with a lot more trees and vegetation—and what the potential health benefits would be.

The presentation—a “design charette” to share work and gather feedback—was given by Harvard T.H. Chan School of Public Health’s Linda Powers Tomasso, who is leading the School’s involvement with a project based at the Harvard Graduate School of Design (GSD) called the Linear Urban Forest (LUF). The project aims to help Springfield—and, eventually, other older cities across the U.S—minimize the “urban heat island” effect. Urban heat islands are city areas with lots of concrete and asphalt that absorb high levels of solar radiation and have few trees to provide shade, resulting in temperatures that can be 10-12 degrees higher than areas with more vegetation.

“Without natural spaces, heat gets concentrated, and that concentration of heat—which is worsening due to climate change—is dangerous for people to live in, recreate in, and work in,” said Tomasso.

The LUF—led by the GSD’s Martha Schwartz, a landscape architect, and supported by Harvard’s Climate Change Solutions Fund—is an interdisciplinary effort launched in April 2021 involving landscape designers, U.S. Forest Service biologists, municipal policy practitioners, and Harvard Chan environmental researchers. The group designed a linear urban forest—connected lanes of trees, shrubs, ferns, and other vegetation running along sidewalks or portions of streets—and plans to quantify its climate- and health-related benefits for U.S. cities, using Springfield as a pilot. The long-term goal is to help cities mitigate heat, reduce heat-related health harms, and improve residents’ overall health and well-being.

Tomasso and John Spengler, Akira Yamaguchi Professor of Environmental Health and Human Habitation, were initially brought into the project to help calculate the health benefits of greening Springfield streets. Over the course of their work, they got the idea of producing visualizations of Schwartz’s landscape design that could be presented to Springfield residents, to offer them a “you-are-there” picture of what it would be like to live amid more greenery, talk about how it could improve their health, and gather their feedback. Tomasso and Spengler applied for and won a $30,000 National Institute of Environmental Health Sciences grant to create the visualizations, with help from colleagues from the Visualization Research and Teaching Laboratory in Harvard’s Department of Earth and Planetary Sciences.

“Climate change is here and we need a process to engage citizens in creating adaptation strategies to cool their neighborhoods,” said Spengler. “Digitally created street images of how streets could be transformed offered people the opportunity to express preferences and co-create their neighborhoods.” He’s excited about the project’s innovation potential. “Creating digital images of neighborhoods allows us to project the future,” he said. “We are creating a new pedagogy for involving citizens and civic leaders, giving them a realistic sense of what adaptations to climate change might look like at the neighborhood scale.”

“This project—which we call ‘Visualizing the Impact of Urban Street Trees to Cool Cities’—has allowed us to have on-the-ground collaboration with the Springfield community,” said Tomasso. She noted that, sometimes, when cities are planning infrastructure improvements, residents’ concerns aren’t adequately considered. “It’s a matter of environmental justice,” she said. “For researchers, community involvement is often the missing component of translating evidence-based recommendations.”

Health and environmental benefits

Planting more trees and other vegetation in urban environments can have many benefits, said Tomasso. “If it’s not quite as hot, people would be inclined to be outside more,” she said. “Nature can mediate the temperature, provide shade, and make it pleasant to socialize. It also might prompt people to engage in more physical activity than they would otherwise. Those are some of the direct benefits.” Being more active and more social can also have indirect health benefits, she noted. Studies have shown that living near green spaces can lower the risk for health problems such as heat stroke, cancer, heart disease, hypertension, obesity, diabetes, and asthma, and can improve mental health.

Other benefits of the LUF project include better management of stormwater runoff, decreased energy bills, increased quality of life and walkability, reduced greenhouse gas emissions, and increased carbon sequestration.

3D street views

From left: Dillon Escandon of ReGreen Springfield with lidar scanner on his shoulders, Linda Tomasso, and John Spengler
From left: Dillon Escandon of ReGreen Springfield with lidar scanner on his shoulders, Linda Powers Tomasso, and John Spengler

To choose which Springfield neighborhoods to focus on for the visualizations, Tomasso looked for areas with the least shade, the highest levels of asthma, and populations of lower socioeconomic status. She zeroed in on Upper Hill, a densely populated low-income neighborhood with aging housing and limited recreational space. Last summer, she and colleagues walked through the neighborhood, capturing visuals using a mobile lidar scanner. The device sits atop a user’s shoulders, emitting laser pulses that bounce off roads, pavement, and structures. Each pulse returns to the scanner, and that data enables the creation of 3D visualizations of the real world.

The lidar scanner images, along with street images from Google Earth, provided a pictorial basis for the visualizations. Tomasso also consulted land use maps from the city of Springfield; scanned scientific literature for biophysical metrics about annual tree growth rates, evapotranspiration (the process by which water moves from the land surface to the atmosphere via evaporation and transpiration from plants), albedo (the reflectivity of surfaces such as streets, rooftops, and trees), and building intensity (the number of dwellings per acre); and used Stanford University’s Natural Capital Project model to generate estimates of city-wide ambient temperature cooling that could be expected if the urban forest were created.

Based on that wealth of data, Kachina Studer, a digital technology specialist in the Visualization Research and Teaching Laboratory, created a series of visualizations for residents to view.

Seeing the trees

Three visualizations of Albemarle Street in Springfield. From the top down: the current street; the street in 2070 with trees planted every 20 feet; the street in 2070 with trees 15 feet apart in double rows, with understory plantings.
Three visualizations of Albemarle Street in Springfield. From the top down: the current street; the street in 2070 with trees planted every 20 feet; the street in 2070 with trees 15 feet apart in double rows, with understory plantings.

Tomasso held two design charettes for residents in Springfield, each drawing about 20 participants. They gathered at the headquarters of ReGreen Springfield, a nonprofit aimed at reforestation in the city and a partner in the LUF project. After an introduction from David Bloniarz—president of ReGreen Springfield, project coordinator for the USDA Forest Service Urban Natural Resources Institute, and an adjunct professor at the University of Massachusetts  Amherst—Tomasso walked the groups through visualizations of what Albemarle Street, a residential street, would look like by the year 2070 under several scenarios. For example, one scenario showed trees planted 20 feet apart, another showed trees planted 15 feet apart, along with smaller plantings in and around the trees.

The presentation inspired a lot of ideas from the participants, Tomasso said. They talked about how the urban forest could create spaces for community gardens, for benches where people could socialize, and for bike paths. They had questions: Could the addition of trees help calm traffic on their streets? Would more trees mean there wouldn’t be enough room to park all their cars? The conversation also touched on some of the reasons why there were few trees on the streets: Some were felled by a 2011 tornado, and some were cut down by residents who didn’t want to rake leaves.

One participant’s comment was particularly telling. She said that the visualization with trees made her think “wealthy neighborhood,” whereas the visualization depicting the street as it is now—with just a sprinkling of trees—made her think “poor neighborhood.” “When you drive through neighborhoods where there is a complete lack of vegetation, there is a sense of economic degradation,” she said.

In addition to meeting with residents, Tomasso made a separate presentation to Springfield officials, including the mayor, finance director, and representatives from the public works and parks departments. Their overall response was positive. As a first step, the city plans to do a pilot test to see which tree species will survive best on Springfield city streets. “The trial plots are going in the ground this summer,” said Tomasso. “I’m not certain that would have happened without [the officials seeing] the visualizations.”

Going forward, the hope is that the visualizations will prove useful in other cities around the U.S. to show both residents and city leaders what’s possible. For now, Tomasso is grateful for having had the opportunity to connect with people in Springfield.

“I feel like the meetings gave the community the chance to be an active partner in the design process, in potential changes in their neighborhood that can impact their health,” she said. “For me—as a health researcher that has an interest in nature, and how we can bring communities in on a project like this and partner with them from the ground up—it was very satisfying.”

Karen Feldscher

Photos of design charette and lidar scanner: ReGreen Springfield
Visualizations: Visualization Research and Teaching Laboratory, Harvard University