Which Populations Were Hardest Hit by the Heat Dome?

We're still learning from BC's deadly "heat dome" in 2021, including who's at highest risk from future climate change-driven weather events.


For residents of British Columbia, the 2021 heat dome was an unprecedented week of extreme heat and fatigue that will not be forgotten anytime soon. While the climate anomaly was experienced throughout western North America, the effects were particularly brutal in BC, where between 600 to 740 people are thought to have died due to the extreme heat — making it one of Canada’s deadliest-ever weather events.

With increasing evidence that the event was linked to climate change, it is apparent that we must prepare ourselves for future heat waves of this magnitude. One way of doing that is through exploring novel methods of protecting the human body from extreme heat. However, to effectively do this, we must know who is most at risk from the heat.

Who is most vulnerable?

Unsurprisingly, the most at-risk population during the 2021 heat wave was elderly adults, with nearly 70% of the decedents being 70 or older, according to a government report commissioned following the heat dome. However, a new study published in the journal GeoHealth suggests that certain chronic diseases were also associated with greater mortality during the 2021 heat wave, or Extreme Heat Event (EHE).

Comprised largely of researchers from Environmental Health Services at the British Columbia Centre for Disease Control, the study found that individuals with schizophrenia were at a much higher risk of death during the 2021 EHE, as were individuals with chronic kidney disease and ischemic heart disease — though at lower rates.

Exploring the history

To understand the links between chronic diseases and EHE mortality, the researchers examined the 1,614 recorded deaths in British Columbia between June 25 and July 2, 2021 — the peak of the heat wave — and compared them to recorded deaths during the same time period in earlier years ranging from 2012 to 2020. They referred to the former as EHE deaths, and the latter as typical weather deaths.

Next, they used data from 21 chronic disease databases maintained by the BC Ministry of Health to understand the prevalence of these diseases amidst the EHE and typical weather deaths. These included diabetes, asthma, heart disease, epilepsy, schizophrenia, dementia, and many more.

What did they find?

When compared to previous typical weather years, the researchers found that the odds of death during the heat wave were over three times higher for those with schizophrenia: the largest discrepancy among all of the chronic diseases. A smaller but similar pattern was found for those with chronic kidney disease and ischemic heart disease.

Additionally, EHE mortality was increased among those with more chronic diseases, though this effect appeared to peak for those with three chronic diseases.

Surprisingly, the odds of mortality during the EHE were actually lower for some diseases, including angina, dementia, and osteoporosis.

The researchers suggested a few possible explanations for this increased risk of mortality among individuals with schizophrenia. Firstly, those with schizophrenia may “lack insight into their own health status”, making it more difficult to respond in a timely manner to extreme heat. Additionally, the disorder is accompanied by a host of social effects, including stigmatization, marginalization, and isolation — all of which have been demonstrated to be risk factors for mortality during heat waves.

As global temperatures rise, international agencies are already warning that heat waves will continue to occur, perhaps more drastically than before. It is crucial that we continue to explore the effects of these extreme weather events on our bodies and societies, and safeguard the most vulnerable from the searing future.

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Borna Atrchian is an MA student in the Department of Political Science at the University of Toronto. Having previously completed a Behavioural Neuroscience degree, he is passionate about issues where politics and power intersect with psychology and human behaviour. He is interested in understanding the conditions that create distrust of the scientific community, as well as finding the most effective ways to rebuild this trust.