A report comparing satellite images of large urban areas over a span of 20 years shows that while many cities are losing their green space, the City of Guelph has increased its urban greenness.
The Urban Greenness Report looks at satellite images from 2001, 2011 and 2019, to track greenness across cities at the three points in time.
The report tracks the same physical spaces using satiate imaging to compare the vegetation coverage with the data broadly representing vegetation across the whole of the city, reflecting parks and other publicly and privately owned green spaces and features.
The level of urban greenness will depend on natural environmental conditions as well as the local land use.
“With this data, especially with the time-series data, it allows cities to get one metric or one indicator on what is happening to vegetation, especially if they couple it with on the ground knowledge that they have for their city,” said Jennie Wang, one of the authors of the report. “They can use this as one metric to see, you know, our vegetation in one case may be going up and try to explain that.”
Guelph was among the few cities analyzed in the report that saw its greenness increase over the nearly two-decade period, with each satellite imaging period showing an increase in the greenness.
In Guelph, that urban green space number went from 79 per cent in 2011, to 80 per cent in 2011 and up to 86 per cent in 2019.
In large urban population centres, an average of 70 per cent of the total land area was classified as green.
Average urban greenness was 78 percent in medium population centers and 87 percent in small population centers. In over one third of small population centres, the entire area was classified as green.
According to the report, greenness was assessed for nine weeks from June 25 to August 26 for the reference years 2001, 2011 and 2019 for the same physical area using the 2016 population center boundary to ensure consistency.
Wang said there are numerous benefits to the city’s work within urban green spaces, such as the filtering of polluted air and the reduction of heated zones.
“We have seen benefits of increased vegetation on mitigating urban heat islands, and that can be particularly important when we look at something like the extreme events we have seen in some recent time periods, like this past summer in BC we had the what dome in late June,” said Wang. “SO having areas with some vegetation can provide some of these shelters or at least areas that can help mitigate and reduce the need for cooling.”
Of the cities undertaken in the study, the greenness of Guelph in 2019 was tied with both London, ON and Victoria, BC
Eight cities studies had a higher percentage of urban greenness in 2019.
“Green spaces are essential to building the resilience and liveability of cities through the ecosystem goods and services they provide. For example, trees and other vegetation can improve urban air quality, mitigate urban heat island effects, reduce or delay stormwater runoff, provide wildlife habitat and provide recreational opportunities and aesthetic benefits,” the report reads. “Urban greenness reflects the presence and health of vegetation in urban areas and is a measure of urban ecosystem condition.”
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