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Over 500 Excess deaths from a heat dome in British Columbia, Washington and Oregon

An unprecedented heat dome trapped hot air over much of southern British Columbia, Canada and Oregon and Washington in the United States, in the week of June 25 – July 1, breaking temperature records in the usually temperate region. A towering ridge of high-pressure air cut off the normal flow of cool, moist wind from the Pacific Ocean, diverting the jet stream to the north, and warming the air by compressing it and funneled hot, dry air from the eastern arid side of the volcanic Cascade Mountains (Figure 1), causing widespread temperature anomalies exceeding 20oC, shown in Figure 3.

Figure 1. Heat dome over northwestern North America, 1 July 2021. Source:, 2021.

Temperatures in Lytton, British Columbia (Figure 2) reached 49.6oC on June 29 and set a Canadian all-time record before the town was burned to the ground by a bushfire the next day.

Figure 2. Left: Location of Lytton (red dot, top right corner) northeast of Vancouver, British Columbia (bottom left corner); bottom edge is the U.S. border. Right: Lytton fire. Source: CBC.
Figure 3.  Average 3 day 2m temperature anomaly (degrees Fahrenheit) June 28-30, referenced to 1978 – 2000. Source:

Temperature Record Broken in Lytton B.C. on 29 June 2021

The extreme heat has no precedent in modern record-keeping (Rohde, 2021). Figure 4 shows a pronounced temperature spike compared to the historical record, a breakout far above all previously measured values, to set a new national temperature record for Canada of 49.6 °C. Robert Rohde (2021) stated that this heatwave has reached further above historical means than any other summer heatwave previously recorded anywhere in North America. To put the temperature into context, the all-time high temperature record in Las Vegas, Nevada, located in the desert southwest of the United States, stands at 47.2oC. British Columbia broke that record this week. The following accounts are based on reporting from the Canadian Broadcasting Corporation (CBC).

Figure 4. Daily high temperature in Lytton, B.C. Source: Robert Rohde, 2021.

Lytton Fire of 30 June 2021

The people of Lytton had been warned of a fire, 123 acres (50 ha) in size, which was burning south of the village. Officials watched warily as it grew and inched towards the community of 250 people. But it was a new fire, fanned by strong winds gusting up to 71 kph, that surprised town officials, burned through the community and engulfed buildings within minutes of being spotted (Figure 2 right, and Figure 5). The fire consumed buildings so quickly that residents were not given advance notice to evacuate. Many were already leaving by the time the order came from the mayor at 6pm. Residents saw the thick black smoke filling the valley, grabbed what they could and escaped. Within hours, 90% of the buildings had been consumed by flames. There is speculation that the fire may have been caused by a spark from a passing train, and CN Rail is evaluating the status of its train traffic through the B.C. interior.

The BC Coroners Service has confirmed that two people died as a result of the fire. In a written statement, the service said the investigation is still ongoing but preliminary findings are consistent with the description reported by a family member. Jeff Chapman told CBC News earlier this week that he saw a power line fall onto a trench where his parents were sheltering after flames engulfed their home. After the fire passed, he said he saw their bodies. The BC Coroners Service said it hasn’t received any other reports of deaths related to the fire, but officials have said that some people remain unaccounted for, in large part due to the hasty evacuation of the village on Wednesday night. Chris Manseau, media relations officer with the provincial RCMP, confirmed that investigators were able to enter the village on Saturday.

Figure 5. Lytton before (left) and after (right) the fire. At that intersection was a home, the Canada Post office, the BC Ambulance Service, and a hotel. Source: McElroy, 2021.


The heat dome produced a flurry of bush fires, with crews grappling with more than 62 blazes across British Columbia, a task complicated by the lingering effects of the record-breaking temperatures. Earlier this week, helicopters sent to fight the Sparks Lake fire (Figure 6), which has since grown to more than 20,000 ha in size, were grounded because their engines had overheated. Towering over that blaze were pyrocumulonimbus clouds that can create their own weather systems, including lightning strikes. The dry conditions of the landscape have made suppressing the B.C. fires impossible, and B.C. has pulled back resources to keep fire crews safe. Roads buckled and power cable covers melted under the heat in Washington and Oregon. Heavy air conditioner use knocked out power for tens of thousands of people.

Excess Deaths Attributed to Heat

The B.C. provincial coroner, Lisa Lapointe, reported that at least 719 people died suddenly between June 25 and July 1 during B.C.’s record-breaking heat wave, almost three times the usual number. This suggests that 240 sudden deaths would normally occur in the province over that period, implying excess heat deaths of 479 people. Lapointe said in a statement that heat is very likely a factor in many of those deaths, but that is to be confirmed, and that many of the people who died lived alone and were found in residences that were hot and not ventilated. She said the 719 number is preliminary and will increase as coroners enter other death reports into the agency’s system. Coroners have been delayed in responding to scenes due to a surge in sudden deaths in some areas. The agency has enlisted coroners from its service who typically do not work in the field, and is working to minimize wait times. B.C. had seen only three heat-related deaths in the past three to five years before the heat wave.

Figure 6. Left: Sparks Lake fire (Source: CBC). Right: Lytton, Sparks Lake and McKay Creek fires with snow cover indicated in white (Source: NASA).

“This, frankly, took many of us off guard,” Lapointe said. “Many of our health services, our first responders, we haven’t experienced anything like this in the province previously. It took a bit of time for us to ramp up our response. There were some delays in reaching the coroner and there were some delays in responding to scenes.” Lapointe said the agency will look at patterns in the deaths, including regions where they occurred, the age and sex of the person, any underlying health conditions they might have had and their type of dwelling. The report will also study best practices in other jurisdictions and provide recommendations to the province. Lapointe said it will take a couple of months to complete.

As of Thursday, officials in Washington state had attributed 20 deaths to the heatwave, 13 of them in King county, which includes Seattle. Oregon had recorded 79 deaths attributable to the heat.

The Role of Climate Change on Heatwaves

While this heatwave has been extraordinary in many ways, its birth and evolution followed a well-known sequence of events that generate heatwaves. Christian Jakob, of Monash University, eloquently describes its formation in The Conversation this week (Jakob, 2021):

Eight days ago, it rained over the western Pacific Ocean near Japan. There was nothing especially remarkable about this rain event, yet it made big waves twice.

First, it disturbed the atmosphere in just the right way to set off an undulation in the jet stream – a river of very strong winds in the upper atmosphere – that atmospheric scientists call a Rossby wave (or a planetary wave). Then the wave was guided eastwards by the jet stream towards North America.

Along the way the wave amplified, until it broke just like an ocean wave does when it approaches the shore. When the wave broke it created a region of high pressure that has remained stationary over the North American northwest for the past week.

So, did climate change have a role to play in this event? The answer is most probably yes – as the mean global temperature increases, it increases the probability of hitting extremes more frequently, and reaching extremes that are ‘unprecedented’ in our historical view. But we are still some way from being able to say exactly how climate change will impact the location and intensity of heatwaves, because individual heatwave events are caused by weather patterns – undulations and breaking of the jet streams – not time-averaged climate conditions.

Risk Frontiers does not model weather, but it has been probabilistically modelling losses associated with heatwave and related bushfires in Australia since 2004. The most recent release of our bush and grassfire loss model, FireAUS, uses satellite-derived environmental data with machine learning to model long-term burn probabilities and associated losses for given time-averaged climate conditions across Australia. FireAUS can now also model future changes to bush and grassfire loss probabilities for a range of future climate scenarios. Similarly, PerilAUS, Risk Frontiers’ database of impacts and consequences of natural hazards in Australia, holds records on heatwaves dating back to 1844. It was analysis from this dataset that led to the now oft-quoted datum that heatwaves are Australia’s deadliest natural hazard (see Coates et al, 2014). Many of these deaths directly preceded disastrous bushfires.

References (2021).

Coates, L., Haynes, K., O’Brien, J., McAneney, J. and Dimer de Oliveira, F. (2014). Exploring 167 years of vulnerability: An examination of extreme heat events in Australia 1844-2010, Environmental Science & Policy, 42:33-44

Jakob, Christian (2021)., Justin (2021). Chilliwack Fire Department. (2021).

Rohde, Robert (2021).

About the author/s
Paul Somerville
Chief Geoscientist at Risk Frontiers | Other Posts

Paul is Chief Geoscientist at Risk Frontiers. He has a PhD in Geophysics, and has 45 years experience as an engineering seismologist, including 15 years with Risk Frontiers. He has had first hand experience of damaging earthquakes in California, Japan, Taiwan and New Zealand. He works on the development of QuakeAUS and QuakeNZ.

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