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Public heat warnings have often been impugned for not reaching people soon enough, or worse still, deluging them with contradictory advice

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Destruction along Fraser Street in Lytton, B.C. in early June, nearly one year after a fire destroyed most of the village.Melissa Tait/The Globe and Mail

Heat waves are Canada’s deadliest form of extreme weather, a federal disaster database shows.

And according to the Intergovernmental Panel on Climate Change, the threat they present will only grow amid rising extreme temperatures, continuing urbanization and increasing numbers of vulnerable people. Yet public warnings have often been impugned for not reaching people soon enough, or worse still, deluging them with contradictory advice. And officials whose job it is to respond to the warnings have been criticized for not being adequately prepared to protect people.

Public safety experts love acronyms, and the one they’ve come up with for these two functions is HARS: heat alert and response systems. Such systems are intended to reduce the impact of extreme heat, particularly deaths, by warning citizens to drink more water, avoid outdoor activity or check on granny. But a HARS is about more than just issuing public bulletins: An advisory also needs to kick off responses from public officials, such as extending operating hours of swimming pools, shopping malls, libraries and other facilities where people can cool off, or staffing up 911 centres to handle a deluge of emergency calls

Some HARS clearly leave much to be desired. In June, a death review panel convened by the B.C. Coroners Service concluded last year’s extraordinary heat dome led to as many as 619 heat-related deaths, mostly of older people who lived alone and suffered from chronic diseases. Among its major findings was “a lag” between heat alerts issued by the federal Environment Ministry, and the responses of B.C.’s public agencies.

“We’re really far from being prepared,” said Glen Kenny, a professor at the University of Ottawa who researches heat strain. “And we’re certainly slow on the take when it comes to alerting people.”

The panel’s report said little about the reasons for that lag, nor did it indicate how many of the deaths an effective HARS might have prevented. (The coroners service did not make panel members available for an interview to answer questions about what specifically went wrong.) Nevertheless, the panel urged B.C. to establish a more co-ordinated system.

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The province was already working on it. In a statement to The Globe, Emergency Management BC spokesperson Aimée Harper wrote that B.C.’s new HARS is already able to issue heat warnings, including ones that interrupt television and radio broadcasts. EMBC has also collaborated with health authorities to support individuals most at risk during heat waves, and has developed a guide in multiple languages on how residents should prepare for extreme heat.

“Many of the recommendations from the panel’s report are complete or under way in preparation for this summer,” she wrote.

That some heat alert and response systems underperform is perhaps not surprising. “Some of the first ones in Canada, even internationally, only started in the late 1990s: Toronto, for example, and Montreal,” said Peter Berry, senior policy adviser with Health Canada. “So this is fairly new.”

It’s tough to generalize about the state of Canada’s HARS because like much else in Canada, they’re highly balkanized. Health authorities, municipalities and provinces have their own approaches. That’s not entirely a bad thing: the needs of a rural organization such as Manitoba’s Assiniboine Regional Health Authority should differ significantly from Fredericton’s, which in turn won’t be the same as Vancouver’s.

Health Canada began providing guidance on developing HARS about 15 years ago. Soon afterward, Quebec introduced a system known as SUPREME, which created indicators relating to heat risks including socioeconomic characteristics of neighbourhoods such as population density, or the locations of urban heat islands (areas of a city that are typically hotter than their surroundings). Alberta created its Heat Warning and Information System (HWIS).

Health Canada spokesperson Maryse Durette wrote in an e-mail that HARS coverage has been increasing. According to the ministry’s latest monitoring, 79 per cent of health regions across the country were already issuing heat warnings, or had decided against doing so based on scientific evidence demonstrating that heat wasn’t threatening health in their jurisdiction. That’s up from 73 per cent a few years earlier.

B.C. had been among the laggards: a 2017 study by the B.C. Centre for Disease Control found most of that province’s municipalities and health authorities lacked a comprehensive HARS. “At that time, planning for extreme heat was considered a lower priority because the risk seemed low, there were other competing priorities with fixed resources, or heat response planning was not considered their responsibility,” the panel’s report observed.

Just how many lives are saved by HARS is disputed. Some researchers have found them to be protective during heatwaves in France, Italy, China, India and elsewhere. According to an assessment on, an online data portal administered by Environment and Climate Change Canada and several partners, a heat wave in Quebec in 2018 caused less mortality and morbidity than one in 2010; its explanation included SUPREME, as well as increased adoption of air conditioning and other factors.

“We know these [HARS] can be effective,” Dr. Berry said.

Others have concluded that there isn’t sufficient evidence to demonstrate a measurable impact. A study of heat alerts issued by the U.S. National Weather Service for 20 U.S. cities between 2001 and 2006 found that with the exception of Philadelphia, there was no statistically significant evidence that the harm of those events was reduced. “The effectiveness of these alerts in preventing deaths remains largely unknown,” the authors concluded.

Their point wasn’t that HARS are useless, but rather that improvements were needed. “These results highlight the need to better link alerts to effective communication and intervention strategies to reduce heat-related mortality,” they added.

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Heat alert and response systems face a number of challenges. Even accurately predicting a heat wave is difficult. Of 98 heat waves observed in Quebec between 2010 and 2016, the SUPREME system issued warnings for only 47, meaning it missed more than half. While that might erode its credibility, a hypervigilant heat advisory system could be even worse.

“If they’re triggered too many times, people are going to ignore them,” Dr. Kenny said.

Typically, heat warnings are issued when outdoor temperatures are expected to surpass certain thresholds – for example, 31 degrees for two days in a row, and nighttime temperatures that won’t dip below 20. Setting such triggers is more difficult than it might seem. Most official weather stations are at airports, where temperatures can be significantly lower than in nearby urban environments. But what really matters is what’s happening indoors, where people typically retreat during heat waves.

“Within neighbourhoods, or within regions, you’re going to have a vast difference in temperatures,” Dr. Kenny said. “There’s a few studies that have looked at indoor temperatures, and during a heat wave they can vary dramatically by eight to 10 degrees.” The upshot: Some people might face hazardous conditions well before airport weather stations signal a problem.

Further layers of complexity are introduced because some of the people most at risk during heat waves might be difficult to reach. Not everyone has a Twitter account, for instance, or a mobile phone. Many don’t speak English or French as their first language. Some are socially isolated and may not even answer a knock at the door.

An effective HARS must be tailored to each individual community’s demographics, resources and other characteristics, but many health authorities lack the detailed data necessary to assess their community’s vulnerability to heat. They may therefore lack basic insights such as whether the most vulnerable individuals have air conditioning or can access cooling centres, hydration stations and other resources.

Institut national de santé publique du Québec (INSPQ) produces reports on the health consequences of heat waves for each year during which they occur. Dr. Berry said such regular evaluations are crucial for improving HARS. “Health authorities are very busy and it’s difficult sometimes to do these robust evaluations, but they’re really important,” he said.

Heat alert and response systems are limited in what they can achieve as stand-alone initiatives. Health Canada suggests they’re most effective when combined with longer-term preventive measures such as planting trees or introducing lighter-coloured roofing to help keep neighbourhoods cooler.

“Certainly the heat alerts are good,” Dr. Kenny said. “I do think they have their limits.”

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