A recent World Meteorological Organization report called heat waves the “deadliest meteorological hazard” from 2015 to 2019, affecting people living on all continents, and setting new national heat records in many regions. Canada’s top weather event in 2021 was British Columbia’s record-breaking heat, according to Environment and Climate Change Canada. The temperature in Lytton, B.C., hit 49.6 C on June 29. The following day a wildfire destroyed 90 per cent of the town, killing two people and displacing 1,200 others.

Heat waves also exacerbate existing health issues, including cardiovascular and respiratory disease. They’re associated with increased hospital admissions, psychological stress and aggressive behavior, as well as excess mortality.

During heat waves, the highest temperatures are often found in urbanized areas. Urbanization is almost always associated with an increase in paved, impervious areas, and often a decrease in greenery. Concrete and asphalt roads, and other built materials readily absorb, store and release heat, raising city temperatures, a phenomenon called the urban heat island.

Many studies have shown that urban forests can reduce the urban heat island, and many policies focus their attention on large green spaces. Small green spaces, such as yards, rooftops and small parcels of undeveloped land, can make impressive contributions to lowering urban heat, but they are often overlooked when developing strategies for urban cooling.

The effect of small green spaces

Cities rarely have the opportunity to add large green spaces to help counter the effects of heatwaves. Smaller vegetated spaces, however, can still meaningfully decrease local land temperatures.