Hamish Sandison, the Canterbury DHB's community and public health emergency preparedness co-ordinator, said having an alert system would be "essential" to the DHB's heatwave response plan – potentially helping prevent illness and save lives.
"Heatwaves are dangerous to everyone, especially for particular sections of the community such as infants and children, the elderly, pregnant women, outdoor workers, and people with pre-existing medical conditions."
To define temperature thresholds for the 22 selected locations, scientists from ESR and Victoria University drew on nearly three decades of hourly observation data from MetService weather stations.
After analysing local daily maximum "feels like" temperatures, they identified local "threshold" temperatures that were rarely exceeded for two or more days in a row.
Those thresholds varied across the country, spanning from 24C in Hokitika to 31C in Gisborne, and also accounted for effects like high humidity.
That was a particular risk factor in northern spots, as muggy conditions - much of which are expected this summer - could pose serious health consequences.
"When it's high humidity, our bodies struggle to wick away the moisture from our skin, which is a method we use to cool ourselves down," said Victoria University climate scientist Dr Luke Harrington, who calculated the thresholds.
"That means we can't really sweat, which can lead to heat building up in our bodies."
In previous research, Harrington has found flaws with the traditional benchmark of 25C – purportedly stemming from the claim that beef and dairy cattle start experiencing heat stress at that point – as a catch-all measure for extreme heat.
He argued that "extreme" was instead a relative concept – hence the pilot's wide-ranging thresholds - and there was ample evidence from overseas that people were adapted to the temperatures they were familiar with.
"In New Zealand, a lack of targeted monitoring means we have less data relating to the health impacts of extreme heat than other countries," Harrington said.
"While these monitoring systems are being improved, we have opted to select thresholds for heat alerts that are conservatively high, by international standards."
Following the pilot, the team aim to refine and improve the service for next summer.
"Having an early warning system is a really important step towards reducing the impacts of heatwaves," said ESR scientist Dr Annette Bolton, who has been working on adaptation planning for climate-related health impacts.
"It is only going to get warmer and more uncomfortable for many. The pilot will be a success if we can reduce the number of people suffering heat-related illnesses and going to hospital, or even increase awareness."
