Cities trying to cool sweltering streets often set broad tree canopy targets. But those targets can overlook the reality that not all shade is equally useful, and not every neighbourhood has room for more trees.
Now, two new studies from University of British Columbia researchers offer a more targeted approach. Tested in Kelowna, B.C., the complementary tools can identify urban hot spots down to individual blocks and determine where new trees could deliver the greatest benefits.
"Cities often know they need more tree canopy, but they still have to decide exactly where planting is possible and where shade will make the greatest difference," said Dr. Melissa McHale, a professor in UBC's Faculty of Forestry and Environmental Stewardship and senior author on both studies. "Together, these approaches move us from broad citywide targets toward decisions at the scale of the streets and neighbourhoods where people actually experience heat."
Unmasking 'hidden' heat
Satellite thermal maps give cities a bird's-eye view of surface temperatures, but often lack the detail needed for block-by-block planning. Standard 30-metre pixels can blend the temperatures of rooftops, asphalt, lawns and tree canopy into a single average.
In the first study , published in Remote Sensing, UBC researchers tested an open-source machine-learning technique that sharpens imagery from Landsat and Sentinel-2 satellites to 10-metre resolution.
The higher-resolution maps revealed nearly five times as much temperature variation across Kelowna. With conventional 30-metre imagery, hot spots appeared in broad areas averaging 18,000 square metres, roughly two and a half Canadian football fields. The 10-metre approach detected much smaller hot spots as small as 700 square metres, about the footprint of a large residential lot.
Features of the landscape like tree canopy and paved surfaces explained more than 65 per cent of the additional temperature detail, indicating the method was detecting real landscape differences rather than digital noise. While surface temperature is not the same as air temperature, the freely available approach could help cities identify small hot spots that conventional mapping misses.
Putting shade where it counts — and fits
Finding heat is only part of the challenge; cities also need to know where trees can realistically be planted and provide useful shade.
In the second study , published in Urban Forestry & Urban Greening, the team used CanopyFit, a modelling approach conceived and spearheaded by Dr. McHale and developed collaboratively with the Urban Ecology and Sustainability Lab and her municipal partners, to map practical planting potential. It excludes areas unsuitable for planting, such as buildings, sports fields, underground utilities, wildfire buffer zones and environmentally sensitive ecosystems, then assesses shade potential alongside heat exposure and social and economic need.
Across Kelowna, the model identified space for 248 hectares of potential new mature canopy, but that opportunity was highly uneven. Just 20 per cent of the analyzed area accounted for more than half (50.8 per cent) of all potential shade gains.
The analysis also points to different solutions for different neighbourhoods. Some are "win-win" areas, where high heat and equity needs coincide with ample planting space, identifying areas where additional tree planting could deliver particularly large benefits." Others face high heat and greater need but have little room for new trees, suggesting alternatives such as removing asphalt, changing development rules or installing engineered shade.
Because both approaches use adaptable frameworks and widely available data, municipalities elsewhere can combine them with local information to develop strategies for reducing heat.
"Cities have limited space and resources for planting, so we need to be strategic," said Dr. McHale. "The goal is to establish and sustain large, healthy trees where their cooling and other benefits are needed most. Where the built environment leaves little room for trees, the findings can help cities identify barriers to planting and assess other approaches to providing shade."
