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“2023 was the hottest year on record,” said Daniella Hirschfeld, ASLA, PhD, assistant professor at Utah State University. “But we must also think of a future when 2023 was one of the coolest years this century.”
In the next few decades, we can expect 250,000 excess deaths from extreme heat worldwide each year. People in underserved communities, children, and older adults are at greater risk.
There will also be significant economic impacts. “Already, an estimated 153 billion labor hours have been lost due to extreme heat.”
In an online discussion organized by the ASLA Biodiversity and Climate Action Committee, Hirschfeld said there is one approach that can help cool entire communities. “Nature-based solutions reduce urban heat islands.”
Landscape architects are weaving these solutions into the built environment, increasing our resilience to rising temperatures. They are also developing plans and designs to ensure underserved and historically marginalized communities see benefits in an equitable way.
Earlier this year, Hirschfeld published Landscape Architecture Solutions to Extreme Heat, a study supported by a grant from the ASLA Fund. Her research found that “increasing the number, size, and amount of greenery in a nature-based solution decreases urban heat islands.”
“How these solutions are distributed through a community also matters,” she said. If they are all clustered in one community, then other communities will not benefit. A greater cooling effect is achieved when these solutions are connected.
Her research identified four key design strategies to reduce urban temperatures:
- Increase tree percentage in parks and green spaces
- Provide shade
- Use plant materials and water instead of hardscape
- Switch to green ground cover, including grasses and shrubs
Instead of focusing on individual heat islands, Salvador Lindquist, ASLA, assistant professor at the University of Nebraska – Lincoln, sees them as connected in heat archipelagos or island chains.
In Omaha, Nebraska, these archipelagos form in underserved communities that were once redlined. “These communities are 13 degrees hotter on average.”
Lindquist and his research collaborator Keenan Gibbons, SWA, at SmithGroup, are using technology to understand how dangerous urban heat forms. His goal is to better measure and visualize heat impacts in neighborhoods and catalyze investment in nature-based solutions.
In three communities in Omaha, Lindquist looked at heat and demographic data. He found that “hotter communities also have lower physical and mental health and increased poverty and unemployment.”
He then deployed drones with thermal sensors to develop a 3D view of heat hazards. And he confirmed drone data with readings taken on the ground with hand-held sensors.
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The data and modeling told him that urban environments can be 10-30 degrees warmer than surrounding areas because of concrete and asphalt.
On a moderately warm day, in the mid-80s, he found that a black-colored roof can hit temperatures of 150 degrees, while a white roof can be 30 degrees cooler. A street can reach 113 degrees, but shaded areas can be 23 degrees cooler. “Color and shade make a big difference.”
With support from the Landscape Architecture Foundation and Council of Educators in Landscape Architecture, he and Gibbons will soon release a toolkit on technologies and techniques for measuring heat.
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In New Orleans, Wes Michaels, ASLA, principal at Spackman Mossop Michaels (SMM), also found that heat impacts are not evenly distributed throughout the city. “Some neighborhoods are 20 degrees warmer. And there is no surprise here — social and economic vulnerability and heat overlap.”
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The cause of the heat differences is largely due to the inequitable distribution of trees.
SMM partnered with the local non-profit organization Sustaining Our Urban Landscape (SOUL) to create a highly accessible, equity-focused reforestation plan for the city that provides a roadmap for achieving a tree canopy of 24 percent by 2040.
But more importantly, the plan also seeks to equalize the canopy, so at least 10 percent of all 72 neighborhoods are covered in trees. Currently, more than half of neighborhoods are under the 10 percent goal.
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Michaels said 100,000 trees will need to be planted at a pace of 7,000 trees each year for the next 15 years. “This is infrastructure that needs to be built.”
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A set of pilot neighborhoods are moving the plan forward. Over five years, these communities will grow trees, increase capacity to plant trees, and train local professionals.
In these neighborhoods, engagement is helping to ensure community members understand the goals of the plan and support where trees are planted. “Trees can’t become controversial. If a limb falls off a tree onto someone’s house, that sets back the plan.”
When planting trees in underserved communities, Michaels urged landscape architects to “stop, think, and listen.” He has learned the hard way that “not everyone sees trees the way I do.” It’s important to “go slow and meet people where they are.”
The reforestation plan also calls for the city to create a unified tree policy. “This is an ongoing project to create cohesion between city agencies,” Michaels said. And it also seeks to prevent net tree loss from development or storms.