Using the Urban Forest to Mitigate the Urban Heat Island Effect

In 2011, the City of Kingston, Ontario implemented a forward-looking Urban Forest Management Plan that, in addition to many other benefits, will help to combat the problems posed by extreme heat events and the urban heat island effect. The urban heat island effect is the phenomenon in which an urban space heats up faster, and retains heat longer, than the surrounding countryside. This means that an urban landscape is usually 1° C to 3° C warmer than the surrounding area, with the difference capable of reaching upwards of 12°C in the evening. In addition to adding significantly to air conditioning costs and strain on the electrical system, extreme heat events can pose substantial health risks to people, especially members of vulnerable groups such as the elderly or the homeless. There are multiple means of combating this problem and an aggressive tree planting campaign is a particularly effective one, as trees are a relatively inexpensive means of reducing heat in urban spaces while simultaneously offering many other benefits such as habitat for animals, filtering air pollution, capturing stormwater, and increasing the aesthetic beauty of a space. It is estimated that Kingston’s urban forest generates roughly $1.87 million in such environmental services annually.

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Understanding and Assessing Impacts

The primary motivating factor for this program was the recognition in 2010 that the City of Kingston had lost a sizable portion of its urban canopy. While the city could claim a 21% canopy coverage of urban space, a value similar to the rest of Canada, it was deemed that this value was insufficient for the vision that Kingston had for its future. It was quickly recognized that expanding the tree canopy could offer many valuable environmental services, particularly regarding extreme heat events and the urban heat island effect. The Urban Forest Management Plan was not created specifically to counter these effects, but rather was intended as a catch-all plan that incorporated and built upon the many positive attribute of an expanded urban canopy. It should be noted that although the plan did have a broad goal of increasing the urban tree canopy to 30% coverage, the officials in charge of implementing it took great care to examine the specifics of how and where trees should be planted in order to maximize the benefits they provide. For example, trees were specifically planted at bus stops around the city so as to provide shade for people waiting on transit services. This degree of specificity and detail in the planning process helped the Urban Forest Management Plan to achieve the multiple stated goals.

Identifying Actions

The first step in this process was analyzing the urban forest canopy; this was completed in 2009 and revealed that roughly 21% of the City of Kingston was covered by tree canopy. This was recognized as insufficient and when the official city plan was updated in 2010, it called for increasing the tree canopy coverage to 30%, which is keeping in line with the recommended guidelines set forth by Environment Canada. The Urban Forest Management Plan incorporated these changes and was published in the following year, 2011. Further measures to help increase tree canopy, and reduce the urban heat island effect in general, were also introduced in the 2012 Official Community Plan. Specifically, it provides support for “community-based initiatives such as community gardens and other forms of urban agriculture, and reforestation projects are permitted in all land use designations, subject to site by site evaluation.” Additionally, there are supplementing bylaws and plans that support the health and vitality of the urban forest indirectly, such as the Drought Protection Strategy that helps protect the forest in the event of a drought. When one occurs, a Tree Watering Alert to solicit assistance from the citizens in helping to keep public trees watered and healthy.

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Additional Resources:

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