Analysis of community deaths during the catastrophic 2021 heat dome: Early evidence to inform the public health response during subsequent events in greater Vancouver, Canada

Abstract

Background: British Columbia, Canada, was impacted by a record-setting heat dome in early summer 2021. Most households in greater Vancouver do not have air conditioning, and there was a 440% increase in community deaths during the event. Readily available data were analyzed to inform modifications to the public health response during subsequent events in summer 2021 and to guide further research.

Methods: The 434 community deaths from 27 June through 02 July 2021 (heat dome deaths) were compared with all 1,367 community deaths that occurred in the same region from 19 June through 09 July of 2013-2020 (typical weather deaths). Conditional logistic regression was used to examine the effects of age, sex, neighborhood deprivation, and the surrounding environment. Data available from homes with and without air conditioning were also used to illustrate the indoor temperatures differences.

Results: A combined index of material and social deprivation was most predictive of heat dome risk, with an adjusted odds ratio of 2.88 [1.85, 4.49] for the most deprived category. Heat dome deaths also had lower greenness within 100 m than typical weather deaths. Indoor temperatures in one illustrative home without air conditioning ranged between 30°C and 40°C.

Conclusions: Risk of death during the heat dome was associated with deprivation, lower neighborhood greenness, older age, and sex. High indoor temperatures likely played an important role. Public health response should focus on highly deprived neighborhoods with low air conditioning prevalence during extreme heat events. Promotion of urban greenspace must continue as the climate changes.

Keywords: All-cause mortality; Greenness; Heat dome; Neighborhood deprivation; Urban heat island.

Figure 1.

Time series of daily observed mortality (bars) and daily population-weighted maximum temperature (blue line) estimates for greater Vancouver during the 2021 heat dome. Counts are coloured according to their deviation from expected values (black line), as calculated with the PHIDO algorithm used by the BC Centre for Disease Control. Heat dome deaths were drawn from the 6 days coloured in red, which include June 27 through July 2. PHIDO, Public Health Intelligence for Disease Outbreaks.

Figure 2.

Hourly temperature measurements during the 2021 heat dome in greater Vancouver. These data come from the inland municipality of Abbotsford, where temperatures are usually at least 5°C higher than in the coastal areas. The outdoor measurements (black line) were taken from the weather station at Abbotsford International Airport. The indoor measurements (blue and red lines) were accessed through the ecobee Donate Your Data program (https://www.ecobee.com/donate-your-data/), which allows its internet-enabled thermostat owners to make their data anonymously available for research purposes. There were 11 homes with ecobee data in Abbotsford. The red line shows the worst-case scenario home without air conditioning, demonstrating how temperatures can build to dangerously high levels during an extreme heat event. The blue line shows the best-case scenario home with air conditioning, though data were missing for the days before the heat dome.

Figure 3.

Maps of the heat dome community mortality rate (A), locations in the material and social deprivation categories (B), and greenness within 100 m (C). The crude mortality rate is shown for those aged 50+ in each of the 20 local health areas included in the study. Deprivation categories are shown at the postal code locations for all deaths included in the study, whether they occurred during the heat dome or the typical weather period. Likewise, the NDVI greenness values are shown at the postal code locations of all study subjects. NDVI, normalized difference vegetation index.