Torontoist Explains: How Heat Alerts Work
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Torontoist Explains: How Heat Alerts Work

We know it feels like heat-alert weather, but what does that mean and how does Toronto Public Health respond?

Earlier today, Toronto Public Health declared a heat alert for the city, as temperatures are expected to hit 38 degrees Celsius with the humidex. We all know it’s hot—after all, our fans are on the highest setting, and our ice packs are ready. But TPH deals with hot weather on a different scale, and they have it down to a fine art. Their system for calling heat alerts analyzes both forecasts and historical weather and mortality data to determine whether the public should just wear more sunscreen when they go to the Island, or seek shelter from the oppressive heat immediately.

We asked TPH to walk us through a heat alert: what makes the health unit call one, how it prepares, and what it looks like in action.


What is a heat alert?


Heat and extreme heat alerts are warnings issued by Toronto’s Medical Officer of Health to inform the general public—vulnerable residents in particular—that there will be oppressively hot weather that can be detrimental to their health. Toronto Public Health calls heat and extreme alerts between May 15 and September 30 every year. Last year, TPH had just one heat alert because the summer was uncommonly cool; in 2013, it called seven heat alerts and six extreme heat alerts.


How does TPH determine when to call a heat or extreme heat alert?


Up until this year, TPH relied on its Heat Health Alert System to determine when to call a heat or extreme heat alert. The HHAS was designed specifically for the City of Toronto, in collaboration with the Toronto Atmospheric Fund and the University of Delaware in 2000-2001. It compared forecast data—the expected temperature, humidity, dew point, cloud cover, wind speed and wind direction on a given day—to weather conditions over the years that led to increased heat-related deaths in the city. The HHAS combined more than 40 years of weather-related data and 17 years of mortality data into an algorithm to predict the excess mortality rate.

Under the HHAS, a heat alert was called when the forecasted weather conditions indicated the probability of a high mortality level was between 25 and 50 per cent greater than a typical day. An extreme heat alert was called when the weather conditions suggested that probability was at least 50 per cent greater.

It’s a process that evolved from when Toronto first started issuing heat alerts in 1999. At that time, it used a threshold of a one-day forecast of a humidex of over 40 degrees Celsius.

This year, the heat alert process is changing again. TPH and the nine other health units that are within the Pan Am and Parapan Games’ footprint are piloting a new heat alert system, which will use Environment Canada forecast temperatures to call their alerts. The plan is for all the health units in the province to get on board in 2016.

“The one thing we want is consistency. There are 36 health units across Ontario and some of them have heat warning systems, such as Toronto Public Health, and some don’t,” says Rajesh Benny, TPH’s manager of health hazards and cold and hot weather response. “The federal government, the provincial government, and the various health units wanted to get together to have a consistent system, so that when people are informed of an alert, they know what to expect.”

For example, Toronto had an established program with the HHAS and Peel Region had a similar alert system in place. But York Region, Hamilton, and Durham all had different ways of calling alerts. “This new system is a means of harmonizing all of that,” Benny says.

Under the new system, when there’s a forecast of two days in a row with a maximum temperature of at least 31 degrees and an overnight low of at least 20 degrees, or when the humidex is at least 40 degrees Celsius, then the Medical Officer of Health will call a heat alert. If there are three consecutive days that are forecast to fit that same criteria, he’ll call an extreme heat alert. The new thresholds are based on a Public Health Ontario study that looked at the association between temperature, humidity and mortality across the province to create consistent triggers for calling heat alerts.

Rather than calling the alerts based on forecasts alone, TPH will wait until a day with those conditions has passed. If conditions change between the first and second day, or the first day isn’t as hot as anticipated, the health unit won’t call the alert.


What happens when TPH calls a heat alert?


First, the health unit notifies its hot weather response partners—Toronto Paramedic Services, Toronto Police, the Red Cross, and various community partners—and updates its website and the City’s website. Both Health Connections and 311 provide information on hot weather services.

TPH also has a contract with the Red Cross to hand out bottled water at city parks. The society also does additional outreach work during the heat alerts: representatives drive around to different parts of the city and look for people in stress because of the heat. Toronto’s Shelter Support and Housing also does the same outreach. Shelters across the city allow their clients to stay in air conditioned areas, and drop-in centres with air conditioning extend their hours.

And when the health unit calls an extreme health alert, there’s even more work to be done.


Like what?


During extreme heat alerts, the same heat alert services are still available. In addition, the City opens seven cooling centres at the Centennial Recreation Centre, the Driftwood Community Centre, the East York Civic Centre, the Etobicoke Civic Centre, the McGregor Community Centre, Metro Hall, and the North York Civic Centre. The cooling centres are air conditioned and drinks and light snacks are provided.

In addition to opening cooling centres, some community centres and libraries with air conditioning extend their hours on extreme heat alert days, and so do some city pools. Benny says it’s “relatively easy” for people to get out of the heat. The City also provides TTC tokens to shelters across the city, so low-income individuals can get to a cooling centre.

In an extended period of extreme heat alerts, public health inspectors go to rooming houses, boarding homes and other places that house vulnerable residents to see if there is a hot-weather plan in place, like having a room in the house that’s air conditioned.


How does TPH prepare for heat alert season?


At the beginning of the year, the health unit provides landlord packages to landlords of known rooming houses. The package offers tips on managing the heat, information on the closest cooling centres, libraries, and community centres across the city, and encourages them to set up and promote among residents a designated cooling station in the rooming house. “We encourage landlords to provide a place that people can go and relax during that time of the day when it’s extremely hot,” Benny says.

TPH also has a hot weather response committee that meets twice a year, once before May 15 and once after September 30. It’s made up of different city divisions and community partners, including police, paramedics, the library, the Red Cross, and Change Toronto, which help to plan the year’s heat alert services. In October, they meet again to evaluate the season and determine how to improve next year.


Who is most vulnerable to extreme heat?


Generally speaking, Benny says, people on the lower levels of the socioeconomic scale are very vulnerable to heat: recent immigrants, residents whose first language isn’t English, and people in poor housing conditions, for example, might not have access to the best facilities. For rooming house tenants, it can be incredibly hot in the summer.

Young children, seniors, and isolated people are also particularly vulnerable. “Once we have those alerts being issued, we want people to call or visit family, friends, neighbours,” Benny says. “Especially isolated adults and seniors who are at a greater risk of suffering from heat-related illnesses.”

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