Five ways that cities are adapting to extreme heat

By the time the ball drops on New Year’s Eve, 2024 will have been the hottest year in recorded history. But it likely won’t hold that title for long. Extreme heat is an increasingly persistent reality for most of the world’s population. According to a study published this past spring, there were 76 extreme heat waves worldwide in the previous year, with more than three-quarters of the global population experiencing at least 31 days of atypical warmth as a result.

Protection from extreme heat is not a luxury, United Nations Secretary-General António Guterres told attendees at the COP29 climate conference last week: it is a necessity and a sound investment. In July, Guterres’s office published a call to action on extreme heat, which stated that “the world’s cities are heating up at twice the global average rate due to rapid urbanization and the urban heat island effect.”

Heeding that call to action means cutting carbon emissions, of course. But solutions also lie elsewhere – notably, in better urban design, architecture and planning that mitigates excess heat that’s already a reality and helps reduce heat-related deaths and other detrimental social and economic consequences.

“Cities are where we live, that’s where the heat challenges are,” said Rasmus Astrup, partner and design principal at the Danish landscape architecture firm SLA, one of four expert panellists in a session at last month’s Human/Nature design conference in Toronto called “Forecast for Hotter Cities.”

Astrup is recognized worldwide for climate-adaptive designs rooted in nature. This includes SLA’s work as part of the team that created the framework plan for Toronto’s 520-acre Downsview airport site, the biggest urban redevelopment project in North America. “When we started working on the Downsview airport, we were told that we have to coordinate the whole design so it is fitting with the fact that [Toronto’s climate] would be like Barcelona when the master plan is fully implemented,” Astrup said. “That’s the reality: climate is changing. It’s happening everywhere.”

Astrup’s message, shared by his fellow panellists: “Don’t give up hope. We can do something.” Keeping with that mantra, the group presented an array of innovative ideas, planning policies and design projects from Canada and around the world that cities are now deploying to beat back the heat. Taken together, five key themes emerged.

Bring back nature

Data gathered for many years across hundreds of cities show what most urban dwellers know from experience: locations with ample tree cover and vegetation, particularly parks and ravines, are cooler than areas that are mostly pavement and other impervious materials.

Shade is the biggest factor. But trees also cool the environment by emitting water vapour into the air. Bringing back nature also has the collateral benefit of reducing other urban maladies – flooding, noise, air pollution and stress – while also boosting biodiversity.

Applying a “life-centric approach” to projects is another way to incorporate nature into the city fabric, said panellist Dorsa Jalalian, an associate and senior urban designer at the Canadian firm Dialog. It’s a concept that puts nature front and centre, rooted in Indigenous thinking. “If you just design an ecosystem that’s comfortable for all life to thrive, people are probably comfortable there, too,” Jalalian explained.

Focus on public health and equity

There’s a second correlation that goes with most of the data linking levels of tree canopy and urban heat: namely, that poorer, marginalized, minority populations typically live and work in the hottest areas. “We know that climate change impacts don’t affect neighbourhoods equally,” Jalalian said. “If you take a [Toronto] surface temperature map and the distribution of tree canopy and overlay that onto the socioeconomic data, you can see that wealthier neighbourhoods have better access to tree canopies and more vulnerable lower-income neighbourhoods have poor access to canopies and shade.”

In 2021, the White House directed the Council on Environmental Quality to develop a Climate and Economic Justice Screening Tool. It identifies communities that are overburdened, underserved and disadvantaged on eight metrics, including climate change. The tool is now used by federal agencies to ensure that those areas receive an outsized share of benefits from investments in climate and clean energy.

What’s ultimately needed is a reframing of the problem, explained panel moderator Fadi Masoud, associate professor of landscape architecture and urbanism at the University of Toronto. “Equitable access to shade and comfortable microclimates are often perceived as an amenity but should instead be considered a public health concern,” he said.

Appoint urban heat officers

When it comes to obstacles preventing cities from mounting strong, effective actions to address extreme heat, one of the biggest is a lack of accountability or coordination of efforts across various city departments. A potential solution, according to panellist Owen Gow, deputy director at the Atlantic Council’s Climate Resilience Center in Washington, D.C., is to appoint a chief heat officer.

The idea is to have someone in place who can tackle the issue of extreme heat across the entire city, Gow explained. “Can there be one person who wakes up every day in a city focused entirely on extreme heat; who can go to the health department, the transportation department and start drawing linkages between them?” As the idea catches on, Gow said, chief heat officers also become the face of a city’s response to extreme heat.

To date, Gow said, nearly a dozen municipalities worldwide have appointed chief heat officers. The Climate Resilience Center runs a support network helping the group develop and implement strategies and share ideas. “What’s applicable in Santiago is not applicable often in Freetown or Bangladesh, but there are a lot of commonalities,” he said. The result is an evolving “global playbook” with a set of solutions starting to be deployed around the world.

Rethink city streets

If cities are hottest where there’s pavement, then cooling the biggest paved areas – city streets – is low-hanging fruit in the fight against extreme heat. Technical fixes include using lighter-colour or permeable paving that absorbs less heat. But for larger road networks, “green streets” are a proven solution with the potential to be scaled up exponentially.

“Growing Green Streets” is one of the primary heat-mitigation programs now being rolled out by the City of Toronto’s urban design department. Still in the study phase, the initiative is “really about maximizing opportunities for growing the tree canopy across the city,” said Kristina Reinders, urban design program manager. While green street projects often start by simply adding planters and flower beds with enhanced drainage on sidewalks, more ambitious plans include tree plantings, rain gardens and road narrowing.

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A second option, of course, is to get rid of roads and pavement entirely and rethink planning policies to downplay the focus on cars. “What heats up the streets, what heats up the environment we live in? That’s the cars,” Astrup said.

To illustrate, he showed slides of an SLA project in Manchester, England, that’s still in the design phase. It involves removing the road in an inner-city block and restoring a river bed that had been routed into a culvert and paved over. ‘It’s the asphalt,” he said. “Asphalt is ‘ass’ and ‘fault.’ Why does it have to influence 70% of the space where I live? It is super dumb.”

Mandate thermal comfort

Along with focusing on city streets and pavement, planners and designers are also embracing a more holistic approach, encompassing site plans and building designs, to improve and set standards for maintaining a certain level of “thermal comfort” in public spaces. It’s a methodology that considers four factors that determine how comfortable people feel in an outdoor setting: air temperature, radiant temperature, wind and humidity. Those variables are then combined to calculate a site’s score on a thermal climate index.

In Toronto, designer Dorsa Jalalian is working with the city on a study that will ultimately establish a Toronto-specific methodology to measure thermal comfort, one that incorporates future climate projections. The final guidelines will be “performance-based and not prescriptive,” Jalalian said. “As long as you achieve the target or you are designing with thermal comfort in mind, you can pick whatever works best for your project.”

Brian Banks is a writer and editor whose work focuses mainly on science and nature, conservation, landscape, climate and sustainability.