Discovering the Dual Role of Urban Parks in Combating Heat

Urban parks serve as vital oases in the concrete jungles of Canadian cities, offering respite from rising temperatures driven by climate change and the urban heat island (UHI) effect. A groundbreaking study from Concordia University, published in the journal Urban Forestry & Urban Greening, uncovers how the arrangement of trees within these parks influences cooling differently during the day and night. Conducted in Montreal, this research highlights the need for thoughtful park design to maximize thermal comfort around the clock, providing actionable insights for urban planners and landscape architects across Canada.

Montreal, like many Canadian metropolises, grapples with intensifying summer heat. Downtown areas can be up to six degrees Celsius hotter than greener outskirts such as Mount Royal, exacerbating health risks during heat waves. In 2025 alone, Montreal reported multiple heat-related deaths amid prolonged hot spells, underscoring the urgency of effective UHI mitigation strategies. Concordia's findings emphasize that simply planting more trees isn't enough; their placement and density play a crucial role in balancing daytime shade with nighttime ventilation.

The Science Behind Daytime and Nighttime Cooling Dynamics

The study, titled "Tree Presence and Level of Aggregation in Urban Parks are Associated with Opposite Daytime and Nighttime Urban Cooling," examined 13 diverse parks across Montreal. Researchers deployed on-site sensors to measure air temperature and relative humidity in three distinct micro-environments: open grassland areas, dispersed tree clusters, and large, dense tree aggregations. Wet-bulb temperature—a metric combining heat and humidity to gauge human thermal comfort—was calculated to provide a comprehensive view of park usability.

During the day, especially under sunny conditions, dense tree clusters excelled at cooling. Through shading, which blocks direct solar radiation, and evapotranspiration, where trees release water vapor cooling the surrounding air, these areas significantly lowered temperatures compared to open grass, which absorbed heat and sometimes exceeded nearby paved surfaces in warmth. This daytime benefit is critical as Montreal's humid continental climate amplifies perceived heat, making shaded parks essential refuges.

At night, however, the dynamics reversed. Dense tree canopies trapped residual daytime heat and moisture, slowing radiative cooling and resulting in higher nighttime temperatures. Open grass areas, conversely, facilitated rapid heat dissipation into the cooler night sky, promoting lower temperatures and better overall comfort. This trade-off reveals why a one-size-fits-all approach to greening falls short; parks must accommodate both diurnal cycles for year-round resilience.

Lead Researchers Driving Urban Ecology Innovation at Concordia

Lead author Lingshan Li, a PhD candidate in Concordia's Department of Geography, Planning and Environment, spearheaded the fieldwork. "We often assume that more trees always mean cooler conditions, but our findings show that the configuration of those trees, and the presence of open space, matters just as much," Li explained. Supervised by Assistant Professor Carly Ziter from the Biology Department and collaborators like Associate Professor Angela Kross and Professor Ursula Eicker, the team drew on interdisciplinary expertise in urban ecology, planning, and engineering.

Ziter's Urban Landscape Ecology Lab has a track record of influential work, including prior studies on scale-dependent tree canopy effects and unequal greenspace access in Montreal. This latest publication builds on a related 2025 paper by the same group, which linked hotter neighborhoods to lower-income, racialized areas with sparse vegetation. Concordia's Next Generation Cities Institute fosters such cross-faculty collaborations, positioning the university as a leader in sustainable urban research vital for Canada's growing cities.

Urban Heat Challenges in Canadian Cities: Montreal in Focus

Canada's urban centers face escalating UHI effects, where built environments trap heat, raising nighttime lows by 2-5°C in major hubs like Toronto, Vancouver, and Montreal. Statistics from Health Canada indicate 916 heat-related deaths nationwide from 1981-2022, with projections warning of thousands annually by mid-century absent interventions. Montreal's 2025 heat waves claimed at least eight lives, disproportionately affecting vulnerable groups in heat-vulnerable neighborhoods.

A 10% increase in tree canopy can reduce land surface temperatures by 1.4°C, far outpacing shrubs or grass at 0.8°C, per Concordia's prior analysis. Yet, equity gaps persist: wealthier areas like Outremont boast continuous tree patches for superior cooling, while Montréal-Nord's fragmented greenery leaves residents exposed. This study extends those insights, advocating designs that optimize both cooling supply and demand for equitable resilience.

Photo by Jp Valery on Unsplash

Practical Implications for Park Design and Urban Greening

Urban planners should prioritize structural diversity: integrate mature tree clusters for daytime shade with open grasslands for nocturnal cooling. During heat waves, dense forests risk becoming thermal traps, but balanced layouts ensure parks remain havens 24/7. Li recommends, "A park that meets visitors’ needs at different times of day should be structurally diverse. A balance of mature trees and open grassland can help maintain comfortable conditions both during the day and at night."

This approach aligns with national initiatives like Tree Canada's urban forestry guide, promoting resilient canopies. Cities could enhance models by parameterizing dispersed vs. aggregated trees, improving predictions for retrofits. For instance, avoiding over-forestation in humid climates prevents humidity buildup, as wet-bulb temperatures revealed moderated but persistent differences.

Canada's Urban Forestry Momentum: From Montreal to Coast to Coast

Montreal aims for 25% canopy cover by 2025, planting millions via SOVERDI partnerships. Toronto targets 40%, Vancouver's 2025 Urban Forest Strategy invests in equity-focused greening. These efforts, informed by studies like Concordia's, emphasize species diversity, irrigation, and wind corridors to amplify cooling without nighttime penalties.

• Tree Canada: Planted 80+ million trees since 1992, focusing on UHI mitigation.
• Nature Canada Tree Equity Report: Highlights canopy disparities, urging inclusive planting.
• Health Canada UHI Guide: Recommends vegetation expansion for health protection.

Such programs position higher education institutions like Concordia at the forefront, training future experts through programs in environmental science and urban planning.

Equity and Social Justice in Urban Cooling Design

The study's revelations intersect with social equity. Poorer Montreal neighborhoods endure higher heat exposure due to scant, fragmented greenery, compounding vulnerabilities for seniors, children, and racialized communities. Concordia's October 2025 paper quantified this: continuous tree patches in affluent areas yield superior cooling, mismatched with demand in underserved zones.

Optimizing tree arrangements addresses this by maximizing limited space's efficacy. Policymakers can prioritize vulnerable areas with hybrid designs, fostering inclusive resilience. This research empowers Canadian universities to influence equitable greening policies, bridging academia and municipal action.

Future Directions: Enhancing Urban Climate Models and Research

Future work should explore tree species (e.g., deciduous vs. evergreen), canopy height, irrigation impacts, and variables like wind or cloud cover. Integrating these into models refines forecasts for Canada's diverse climates—from humid Montreal to arid prairies.

Collaborations with cities could test designs in pilots, scaling successes. As Li notes, "Urban green spaces are essential for climate resilience. Understanding how their design affects thermal comfort can help cities make better decisions as extreme heat becomes more frequent." Concordia's role exemplifies higher education's pivot toward applied sustainability research.

Photo by Frederick Wallace on Unsplash

Actionable Insights for Stakeholders and Policymakers

• Planners: Favor 40%+ canopy with open zones for dual benefits.
• Municipalities: Audit parks for aggregation, retrofit for diversity.
• Educators: Incorporate findings in urban forestry curricula.
• Residents: Advocate for equitable greening via community input.

By leveraging this Concordia study, Canadian cities can craft cooler, fairer urban landscapes, mitigating UHI while enhancing livability. As climate pressures mount, such evidence-based designs from higher education research will be pivotal.