As heatwaves increase in frequency and severity around the world, more people are dying during extreme heat events. However, precisely attributing the cause of these deaths to heat has proven to be challenging, which has consequences for how we may understand and account for the significant heat-related health and mortality risks.

In their recently published peer-reviewed article in GeoHealth – authors Liv Yoon, Gregory Richardson and Melissa Gorman provide a reflection on a century of extreme heat event-related mortality reporting in Canada.

KEY FINDINGS

The authors identified six extreme heat events in Canada between 1900 and 2021 with known heat-related deaths. They were identified through an analysis of 206 peer-reviewed journal articles, 340 news-media articles, and grey literature sources. The authors found differences in the amount, type, and depth of mortality data across these six extreme heat events. For example, while age and sex of people who died from heat-related causes were included in almost all reports, there was seldom mention of racial, ethnic or Indigenous identity.

Of the available data, the authors found some common demographic and vulnerability factors about people who died from heat-related causes in more than two of the identified extreme heat events. Aligning broadly with the populations identified as most at-risk in literature, most common heat-related mortalities included people who were:

• 65 years and older
• living alone
• low-income
• who live in urban heat islands (UHI) with little to no surrounding greenspace
• had pre-existing chronic health conditions such as cardiovascular disease, hypertension, and diabetes)
• had mental illnesses – namely schizophrenia, substance use disorders, anxiety and mood disorders

Other factors, such as material deprivation/housing status and lack of access to air conditioning were also commonly found. There was also inconsistent consideration of the compounding impacts of social vulnerability indicators across reports of extreme heat event-related deaths. Factors such as living in areas with high pollution or low green canopy, income level, housing status (security and quality), access to material resources like air conditioning, or social connections were considered more often in reporting after the year 2000, but were inconsistent across time and location, and were limited in scope. This shortcoming is particularly notable in light of the robust body of literature that points to the significant role of social vulnerability in amplifying one’s risk to heat-related morbidity and mortality.

SIGNIFICANCE

A prominent insight was that people with schizophrenia have died at alarmingly disproportionate rates across the two of the most recent extreme heat events in Canada within the six extreme heat events identified (2018 Montreal extreme heat event and 2021 Heat Dome). Informed by this analysis, the first author is leading a study exploring the disproportionately high rates of heat-related mortality among individuals with schizophrenia.

The analysis also found differences in the level of detail amount of mortality data, which may impact the accuracy of reported extreme heat event-related deaths and impact the development of effective preventive measures.  The shortcomings identified may be attributable to differences in the quantity and quality of primary mortality data available across and within extreme heat events in Canada and in reporting practices among various jurisdictions and agencies. Improving the accuracy and consistency of how heat-related deaths are counted and reported is crucial for accurately identifying populations at high risk from heat, which can inform targeted, evidence-based interventions by health authorities.