Edmonton is steadily losing its urban green space, making the city significantly hotter than the surrounding area as temperatures rise due to climate change.
Research by the University of Alberta's Sandeep Agrawal and Nilusha Welegedara has found that between 1999 and 2020, Edmonton lost 15% of its vegetation. The loss is particularly evident in the northern parts of the city, where there is less river valley land and fewer ravines.
This is directly connected to the rise of the urban heat island effect, a phenomenon that occurs when cities replace land with surfaces that absorb and retain heat.
"(Urban heat island spots) correspond with more parking lots, more big box stores, and less trees. Most of the decreases in vegetation have occurred in newly built neighbourhoods because ... vegetation was removed for concrete and roads and things of that nature," said Agrawal, who is the director of the U of A's school of urban and regional planning.
Those changes to the landscape have contributed to summer temperatures that are six to 12 degrees Celsius higher in the city than in surrounding rural areas. Agrawal's research also found that winter temperatures over the 21-year period were up between two and six degrees. While it will be difficult to recover all the vegetation that has been lost, it's important to try to bring some back, Agrawal said.
"The loss of green space and the corresponding rise in the urban heat island effect is entirely due to human activity and urbanization," he explained. "We have seen the heat waves of the last couple of years and the intensity of that is increasing. It is imperative that we think about things that we can manage."
One way to combat the urban heat island effect is to plant more trees. The City of Edmonton has committed to adding two million trees by 2050, a move that's in line with the City Plan and the community energy transition strategy. So far, just over 54,000 have been planted since the goal was approved in December 2020, a city spokesperson said.
Another way is to protect existing trees. A bylaw that accounts for trees on city-owned land will come into effect at the beginning of May, but there is no current protection for trees on private property, though city council has asked administration to provide a report on tools that could be used to that end.
It's important because "even compared to the river valley, private trees make up much more of our urban forest than any other component," said Dustin Bajer, founder of Shrubscriber, a social enterprise that enlists members to fund trees for schools and community groups to plant.
Until the City Charter was introduced in 2018, Edmonton did not have the authority through the Municipal Government Act to regulate private trees outside the zoning bylaw, said Travis Kennedy, the city's general supervisor of open space operations.
Administration is currently in the process of reviewing whether that expanded authority will allow for regulation going forward. Potential options will be presented to the urban planning committee in June.
Protecting private trees would help the City of Edmonton meet its goal of building a tree canopy coverage of 20%.
"So we're talking about doubling the forest canopy," Bajer said. "I think you could even argue that 20% is too low of a number and that maybe we should be reaching for 30% to 40% canopy."
The benefits of more greenery go beyond counteracting the heat island effect, he added.
"Just purely on a well-being standpoint, having access to green space is important," Bajer said. "We also know that the amount of green space is not equitable across cities, and so certain neighbourhoods have more access."
The inequitable distribution of greenery makes some communities are more prone to other environmental challenges, such as flooding. "Green space tends to be permeable and can be an important piece of green infrastructure that can actually do a lot of the heavy lifting so that you don't have to depend on hard, expensive infrastructure to mitigate some of those things," Bajer said.
That's also an argument for spreading green space around instead of confining it to the river valley, though that's also an important part of connecting the city to nature. A move is afoot to create a national urban park in the Edmonton region, with the goal to provide "better access to quality green space for Edmontonians" as well as to act as a nature-based climate solution, Parks Canada said in an announcement on March 14.
As for other solutions that could help with rising temperatures, Agrawal suggested allocating more spaces for parks, or adding green roofs to large commercial and residential developments.
"Hopefully that would help, but obviously it will not bring (the temperature) down to the same level as the rural surroundings," Agrawal said.
Agrawal and Welegedara's research, which was measured using satellite data, weather stations, and other sources, is supported by similar findings by Statistics Canada. Its report shows a decrease in Edmonton's greenness between 2001 and 2019, based on the classification of urban pixels in satellite imagery as green or grey — with grey marking "areas that are predominantly covered by buildings, impervious surfaces, bare soil, and low-density vegetation."
The University of Alberta researchers plan to continue their work on the urban heat island effect, and the next step is to look to the future. They'll be exploring what would happen if various factors changed. The goal is to wrap up their research by this fall.