"It's not surprising," he said. "Heat risk in an urban setting is a combination of medical, social and environmental exposures. The elderly, people with chronic diseases and people with mental health problems are more at risk."

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Kaiser said the social aspect - living alone and not having another place to go to cool down - typically plays a major role in heat-related deaths in the city.

"Montreal is gigantic heat island," he said, referring to an environmental phenomenon caused by a lack of vegetation and an abundance of concrete. There also micro heat islands throughout the city, particularly in some of the poorer areas, he added.