In the first days of July, an intense heat wave hit Quebec. On July 2, Montreal recorded a historic heat record of 36.6°C. The heat wave not only affected Quebec; several records were broken in the United States, Europe and the Middle East, Scotland, Ireland and Armenia.
Unfortunately, the number of deaths caused by heat will only continue to increase. According to a recent study, 30% of the world’s population is exposed to life-threatening extreme heat waves that can last more than 20 days a year. If greenhouse gas emissions continue to increase, 75% of the world’s population will be at risk of heat death by 2100. The deadly heat waves are more common than we think and wreak havoc on more than 60 regions in the world each year. (https://www.nationalgeographic.fr/environnement/).

In urban areas, the temperature can reach several degrees higher (up to 10 degrees difference) than in rural areas. This phenomenon is known as the ‘heat island effect’. In general, we can distinguish three categories of heat islands:
1. The first category is heat on the soil surface;
2. The second is the heat of the urban canopy, that is to say the air between the ground and the treetops. Usually, this happens at night when the ground releases the solar energy absorbed during the day;
3. Finally, the third category is that of the urban boundary layer. This layer of air is located above the urban canopy.

There are many factors that cause heat islands, both human and natural. The lack of plant canopy, non-reflective mineralization (like asphalt), materials that absorb solar energy, etc. are all causes of heat islands. In addition, industrial activities, transportation and air conditioning are examples of human-caused causes that influence the presence of heat islands. City morphology can also affect heat islands, depending on the height of buildings and the presence of automobiles. (https://www.inspq.qc.ca/pdf/publications/988_MesuresIlotsChaleur.pdf).

In Montreal, there has been an increase in heat islands for several years due to densification and mineralization that are reducing green spaces. This also reduces the availability of cool spaces in the city.

Heat islands have several consequences, both in terms of the environment and human health. At the environmental level, heat islands contribute to the development of smog and reduce indoor air quality, which can promote mold, bacterial multiplication, as well as the release of toxic substances from construction materials. Moreover, during periods of intense heat, the demand for energy and water is higher, which has a significant impact on the environment. In addition, heat islands can have serious repercussions on the health of the population, even leading to death. Part of the population is more vulnerable to heat, for example seniors, small children, isolated people, etc. The heat can cause weakness and discomfort, heatstroke and even worsen the condition of people with chronic illness.

To avoid heat islands, many solutions are available to us. Not surprisingly, by greening public spaces and mineralized areas, one can prevent heat islands while enjoying environmental benefits for the city. White or green roofs, green walls, green parking lots, etc. are some examples to limit paved surfaces that favor heat islands. Another solution is to better manage water in the city, to use it for a second use rather than sending it directly into the sewers. Installing fountains can refresh the environment, in addition to creating a pleasant space for the population.

Climate change disrupts the entire planet, especially with extreme heat waves becoming more deadly and more frequent. In the city, the temperature can be much higher than in rural areas because of heat islands. This can have several environmental and human health impacts. Fortunately, several solutions exist and in Montreal, several initiatives have emerged. The green alleys are a good example of a greening project with resident involvement.