In Québec, autumn brings cooler, invigorating temperatures that increasingly contrast with the stifling days of summer. Over time, the negative impacts of climate change are being felt more and more across the planet, and this past summer offered clear evidence of that reality. More frequent and intense wildfires, flooding, record-breaking heat, and increasingly severe extreme weather events are just some of the consequences of our changing climate. In our cities, one of the direct effects of rising global temperatures is the increasing intensity of urban heat islands.

What is a heat island?

An urban heat island (UHI) is a phenomenon that occurs in urban areas where temperatures are significantly higher than in surrounding, less urbanized areas. This is mainly due to the absorption and retention of heat by materials such as concrete and asphalt, as well as by buildings.

The impacts of heat islands

In general, the impacts of heat islands are most evident during the summer and increasingly during the shoulder seasons. Human activities such as vehicular traffic and the use of air conditioning, combined with a lack of green spaces, contribute to rising temperatures in urban areas. The impacts of urban heat islands include, among others, a significant increase in city temperatures, a marked reduction in comfort levels, higher energy consumption, degradation of air quality and biodiversity, and adverse effects on the health of vulnerable populations, placing added pressure on the healthcare system.

Strategies at the city and architectural scales

To mitigate urban heat islands and their effects, several strategies can be implemented, such as creating parks, integrating green roofs, increasing overall vegetation and urban tree canopy, reducing impermeable surfaces, and incorporating water features. The overarching goal is to reduce heat accumulation in cities and improve the comfort and well-being of residents.

In architecture, we have an important role to play in the fight against climate change and, consequently, in the mitigation of urban heat islands. Envelope performance, the choice of green or light-coloured roofs, high-albedo cladding materials, and generous landscape design that promotes surface permeability are just a few examples of the interventions within our reach to help reduce UHIs.

However, combating urban heat islands is a complex challenge that involves everyone, and must begin with stricter regulations and more rigorous land-use planning in certain areas. In general, these measures should aim to prioritize vegetation by limiting mineral and impermeable surfaces, notably through a drastic reduction in single-occupancy vehicle use and by strengthening public transit options. A city should function like a sponge, capable of managing water efficiently by minimizing impermeable surfaces, making it more resilient to climate change and, ultimately, more viable for its population.