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Quebec’s lethal heat spell is coming to an end with a bleak tally of at least 33 deaths and a sharper picture of those whose lives it claimed: Mostly lone, older men who were found in stifling apartments with temperatures as hot as 35 C.

Details on the victims emerged as public-health officials focused on how to deal with weather disasters such as heat waves that are expected to increase in frequency.

“With climate change, heat waves will probably be much more frequent, and we’ll have to adapt,” Horacio Arruda, Quebec’s director of public health, said in an interview on Thursday. “Most people will survive them without any problem. But for others with risk factors, they can kill them.”

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The extreme weather was forecast to peter out on Friday after blanketing swaths of Quebec in stifling heat and humidity for a week. Thursday offered no respite, with temperatures rising to a record-breaking 34 C in Montreal and the humidex factor making it feel like a punishing 45 C.

Health officials put the province’s death toll at 33 on Thursday, and Dr. Arruda said he expects the number to keep climbing in coming days as reports from front-line health workers filter in.

In the meantime, the profile of the 18 who died in Montreal has become clearer. They were overwhelmingly men aged 53 to 85 who lived alone and had health issues such as schizophrenia or heart disease.

Their housing conditions increased their vulnerability. Most lived on the upper floors of multistorey buildings, where heat rose and became trapped.

When ambulance technicians entered their apartments, they found smothering conditions with no air conditioning and temperatures exceeding 30 and even 35 degrees.

For someone with a chronic disease, “it’s highly likely that heat is what put them over the edge,” said David Kaiser, a physician with Montreal’s public-health department.

Dr. Arruda said the victims were alone. “If you have health problems, you might not realize you’re in the process of deteriorating.”

Geography mattered as well. Most of the homes were in heat islands – zones with little greenery and expanses of concrete that trap heat. They were in densely built neighbourhoods such as Parc Extension and Hochelaga-Maisonneuve that ring central and eastern Montreal.

“If you live in the suburbs in a house with a pool and air conditioning, you’re not facing the same conditions as someone who’s unemployed and living in downtown Montreal in a small apartment on the fourth floor, where it’s very, very hot,” Dr. Arruda said.

Parts of Ontario have also been baking in sweltering temperatures but, unlike Quebec, the province has not declared any heat-related deaths. That may be because the two provinces differ in their approach to this week’s weather disaster.

In Quebec, as soon as meteorologists predicted a searing heat wave early in the week, public-health authorities directed front-line workers to pass along reports of deaths they considered heat-related. The measure was intended to help officials target their prevention efforts as the heat wave progressed.

For example, firefighters in Montreal were dispatched to knock on thousands of doors to check on residents of zones considered at risk.

“It let us activate our prevention measures more rapidly,” Dr. Arruda said. The figures were made public “from a principle of transparency.”

Ontario is not releasing data on deaths during the heat wave. Officials say they do not conclude a cause of death until autopsies are performed, a process that could take at least three months.

“I can’t confirm any deaths due to the heat wave,” said Cheryl Mahyr, spokesperson for Ontario’s Office of the Chief Coroner. “Otherwise you’re asking our office to speculate, and we don’t deal in speculation.”

Heat waves such as those endured by central and eastern Canada this week are expected to become more intense, more common and stretch to larger parts of the planet, because of climate change. They are also expected to have increasingly deadly effects. Studies have found that the number of lives lost in heat waves has increased.

Environment Canada is calling for a high of 23 C in Montreal on Friday, and temperatures below 30 degrees in the early part of next week.

With a report from Victoria Gibson

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