Since the turn of the century, cities have grown upward and outward as urban populations increased. Although urban development can enable prosperity, education, and culture, it may also negatively impact human health with increased levels of air pollution, noise, and crowding. Green spaces, which are urban areas that include trees or other vegetation, can mitigate negative impacts of urbanization by providing various ecosystem services, such as heat reduction and air purification, as well as improve public health and wellbeing.
Despite ongoing research that continues to emphasize the importance of green spaces, the understanding of long-term urban vegetation (i.e. greenness) dynamics across Canadian cities is limited. Studies to date have typically focused on the current state of urban greenness in individual cities, using variable methods that limit regional comparisons.
Developing the Urban Greenness Score
In partnership with Dr Nicholas Coops in the Integrated Remote Sensing Studio and colleagues at the Canadian Forest Service, I developed the urban greenness score, which is a comprehensive and accessible framework to understand the current state of urban vegetation and its historic change. The data used for this framework is based on regionally calibrated green vegetation fractions extracted on a yearly basis from the open and longstanding Landsat satellite imagery archive. Using these annual fractions, the multi-decadal change in greenness was calculated and classified as a negative, positive, or no change. The current state of greenness describes the most recent green vegetation fraction and is classified as a relatively low, moderate, or high level.
I applied the urban greenness score on the neighbourhood level to 18 major Canadian urban areas from 1984 to 2016. My results showed that Canadian urban greenness overall decreased since 1984 and exhibited a moderate level of greenness in 2016. However, greenness changes were mostly located along the city’s edge with localized pockets within the urban core, which emphasizes the close link between urban development and vegetation.
Regional differences in urban greenness and its long-term change were also apparent using the score, whereby the Prairies observed the greatest increase in greenness while Central Canada experienced the greatest loss. Despite a decrease in greenness on the west coast, including in Vancouver, greenness levels generally remained relatively high by 2016. Further city level patterns of the score highlight the complexity of intra-urban greenness dynamics that are influenced by varying historical and ongoing factors, such as municipal planning, housing demands, or individual homeowner decision making.
At a relatively low cost, the urban greenness score provides succinct and reliable information about long-term urban vegetation dynamics across Canada. It is also readily available to implement in cross-regional interdisciplinary research, such as epidemiological studies that analyze changes in health status in relation to urban vegetation dynamics.
Applications for this Research
City officials can also take advantage of this otherwise unavailable Canada- wide urban vegetation information to enhance strategic, evidence-based, and sustainable urban plans and policies. Residents are able to access the urban greenness score information to see how vegetation in their own neighborhood and city has changed over the past thirty years. With continued updating, the urban greenness score has the potential to serve as an open-access and consistent monitoring tool to better understand how cities and their vegetation change over time.
Agatha Czekajlo is a recent MSc graduate of the Integrated Remote Sensing Studio with Professor Nicholas Coops. She can be reached at firstname.lastname@example.org.