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Photo Credit: Courtesy of University of Leeds
Scientific Frontline: Extended "At a Glance" Summary: Urban Treescape Cooling Dynamics
The Core Concept: Urban treescapes act as critical thermal regulation infrastructure by significantly reducing ambient temperatures and mitigating harmful heat exposure in built-up city environments.
Key Distinction/Mechanism: Unlike "grey spaces" built with heat-retaining materials, areas with dense tree cover lower surrounding air temperatures through dual physical processes: direct solar shading and evapotranspiration. During evapotranspiration, trees draw groundwater through their roots and release it as cooling water vapor from their leaves.
Major Frameworks/Components:
- Thermal Differential: Treescapes maintain an average temperature reduction of 1.4 °C compared to surrounding urban streets, with peak differentials reaching up to 6 °C during extreme heat events.
- Evapotranspiration: A biological cooling mechanism relying on water transport from soil through vascular tissues to stomata, facilitating atmospheric cooling upon evaporation.
- Heat Exposure Mitigation: Dense urban tree canopies reduce hours of harmful human heat exposure by up to 96% when contrasted with adjacent built environments.
- Microclimate Mapping: The utilization of granular, 15-minute interval sensor data across varied urban environments to construct high-resolution thermal profiles.
Branch of Science: Urban Climatology, Environmental Science, and Plant Physiology.
Future Application: Informing data-driven urban planning, integrating green infrastructure into public health protocols for extreme heat events, and developing climate-resilient municipalities.
Why It Matters: As global temperatures rise and urban heat island effects intensify, protecting and expanding urban tree canopies provides a highly effective, nature-based strategy to improve human thermal comfort and protect vulnerable populations from severe heat exposure.
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| Dr Jim Parker installs a sensor in a tree to capture air temperature and humidity. Photo Credit: Courtesy of University of Leeds |
Trees in urban areas are highly effective in reducing harmful heat exposure and improving outdoor comfort in cities, according to a new study.
Weather measurements in Leeds have shown that many green spaces, such as parks, gardens, and forests, were cooler than surrounding urban environments, also known as gray spaces.
Treescapes—areas with tree cover—were around 1.4 °C cooler on average compared to nearby built-up streets. During the hottest summer periods, treescapes were up to 5 °C cooler in the middle of the day.
The study, published in People and Nature, was a collaboration between researchers at the University of Leeds and Leeds Beckett University, as part of Dr. Jim Parker’s Future of UK Treescapes Fellowship funded by UK Research and Innovation (UKRI).
We need to take the role of trees and green spaces in our towns and cities more seriously—these aren't just nice to have; they are critical infrastructure.
Crucially, the findings conclude that trees dramatically reduce harmful heat exposure, with treescapes seeing up to 96% fewer hours of such exposure than the nearby gray spaces.
Dr. Cat Scott from the University of Leeds School of Earth, Environment, and Sustainability, who was a coauthor of the paper, said, “A key part of making our towns and cities more resilient will be to improve people's access to cooler spaces. As our findings suggest, the protection and expansion of urban tree cover is a key strategy for improving public health, thermal comfort, and the climate resilience of our towns and cities.
"We need to take the role of trees and green spaces in our towns and cities more seriously—these aren't just nice to have; they are critical infrastructure.”
Measuring Weather Conditions
The researchers installed a network of sensors across Leeds, measuring air temperature and humidity every 15 minutes through the summers of 2023 and 2024. The sensors were on busy streets, small city center parks, larger suburban parks, and different types of treescapes, such as larger woodlands or small groups of trees.
One sensor was installed in a mature tree at the University of Leeds Gair Wood site in North Leeds, providing a rural treescape dataset for the study. By comparing conditions across these locations, the researchers were able to explore how temperatures varied during warm summer periods.
The cooling ability of trees is due to the shade they provide and the process of evapotranspiration—where trees take water from below the ground via their roots, transport it through their tissues, and release it through tiny holes on their leaves. Once at the leaf surface, water can evaporate, which cools down the surrounding air.
Recent Heatwaves
Professor Jim McQuaid at the University of Leeds School of Earth, Environment, and Sustainability, who coauthored the research, said, “We are already seeing the impacts of climate change on summertime temperatures in the UK. This summer has seen records smashed across the UK, with four heatwaves already on the books this year. We are looking forward to analyzing the most recent data from the sensor network, which continues to provide a highly detailed map of the temperatures across the city.”
In the past few months, the sensors indicated urban woodlands relatively close to the city center had significantly lower temperatures than the surrounding built-up areas. When the Leeds city center reached a peak of 34 °C on June 26, Batty’s Wood in Woodhouse Ridge was over 6 °C cooler, and Fox Wood in Roundhay was 5.5 °C cooler.
In Headingley, a weather station on a Leeds Beckett University building rooftop saw the temperature reach 32.8 °C, while just hundreds of meters away, measurements in Church Wood showed it was only 27.3 °C at the same time.
Dr. Jim Parker from Leeds Beckett University, who led the study, concludes, “Our evidence shows that planting and protecting trees is a practical and effective way to make cities safer, healthier, and more comfortable, especially as our climate continues to warm.”
Published in journal: People and Nature
Title: Comfort in the canopy: How urban treescapes affect human thermal comfort in a temperate climate
Authors: James Parker, Catherine E. Scott, James B. McQuaid, and Thomas J. Sloan
Source/Credit: University of Leeds
Edited by: Scientific Frontline
Reference Number: as073126_01
