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.