Simply put, developed urban areas tend to be warmer than their surrounding rural or less developed regions. Urban areas are a complex interaction between human-made infrastructure and the natural world. Our day-to-day activities create heat – think about car engines, air conditioner exhaust or streetlights. Not only this, but cities often amplify heat through solid surfaces like concrete or pavement, which absorb more heat and radiate it back into the surrounding environment. Combine these factors with altered wind patterns from tall buildings, and all this heat can have a hard time escaping, unlike in a forest or less developed area.
Urban Heat Islands have many negative consequences. They lead to a reduction in ecosystem services, such as air and water filtration, waste decomposition and pollination. UHIs increase the cost and energy consumption necessary to cool buildings, elevate the emission of air pollutants and greenhouse gases and reduce water quality.
On top of those environmental concerns, UHIs can lead to impaired human health, such as respiratory difficulties, heat exhaustion and heat stroke (United States Environmental Protection Agency, 2023). When resources to cool down are not readily available to all, these conditions can be even more severe, and heat waves can become life-or-death situations. As temperatures and the frequency of heat waves increase with climate change, the effects of UHIs are compounded.
How you can help reduce Urban Heat Island effects
One of the main ways to reduce the impacts of the UHI effect is by planting trees to increase canopy cover! Trees help cool their surrounding areas in four different ways:
- Tree canopies cool urban areas by blocking sunlight and creating shade. Tree canopies help reduce the amount of sunlight that reaches hard surfaces like concrete, which absorb heat and increase the UHI effect.
- Trees help cool urban areas by releasing water vapour into the air through evapotranspiration. Evapotranspiration is the process of water moving from the land as a liquid to the atmosphere as a vapour (gas). Tree roots take up water from the soil, the water moves throughout the tree and is then released as vapour into the air through the leaves. As water turns from liquid to vapour, it absorbs heat and increases moisture levels in the air, which helps cool down surrounding areas and reduce the UHI effect.
- Trees fight the UHI effect by reducing energy consumption. When trees are strategically planted to shade buildings or air conditioning units, less energy is then required to cool those buildings. This decreases energy consumption, which in turn lessens greenhouse gas emissions that exacerbate the UHI effect.
- Trees help cool urban areas by maintaining more porous natural surfaces like soil. Areas that are planted with trees in urban areas are not converted into hard surfaces like concrete that absorb heat and worsen the UHI effect.
Homeowners can help grow the urban forest and reduce the UHI effect in their community by planting trees on their property! LEAF's subsidized Backyard Tree Planting Program has been helping homeowners plant trees on their property for less for almost three decades. In fact, LEAF has added more than 16,500 trees to the urban forests across Toronto, York Region and Durham Region! With a focus on planting the right tree in the right place, LEAF trees are set up to survive and thrive long term, so that we can enjoy all their benefits like UHI effect mitigation.
Of course, trees help with more than just reducing UHI effect. Check out the Ontario Residential Tree Benefits Estimate tool to learn more about the different benefits a new (or existing) tree could offer.
Interested in planting a tree to help combat UHI effect for less this year? Check out our Backyard Tree Planting Program and sign up for a consultation with one of our arborists today.
Joel Sloggett is the Residential Planting Programs Field Assistant at LEAF.
LEAF offers a subsidized Backyard Tree Planting Program for private property. The program is supported by the City of Toronto, the Regional Municipality of York, Durham Region, the City of Markham, the Town of Newmarket, the Regional Municipality of Durham, the Town of Ajax, the Township of Brock, the Municipality of Clarington, the City of Oshawa, the City of Pickering, the Township of Scugog, the Town of Whitby and Ontario Power Generation.