20 Dec 2022

Extreme heat alerts: MetService-led summer trial to cover 44 centres

10:09 am on 20 December 2022

By Jamie Morton of NZ Herald

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New Zealand is moving closer to establishing a national warning system for extreme heat, with a pilot programme planned for nearly 50 centres this season. Photo: RNZ / Tracy Neal

Extreme heat alerts are ready to be issued across nearly 50 centres this summer, as New Zealand moves closer to a national warning system for hazardously hot weather.

A smaller MetService-led trial last summer marked the country's first step towards a heat alert regime that other countries like the UK and Australia already have in place.

This time, local thresholds have been developed for 44 locations, spread from Kaitaia to Milford Sound.

Alerts will be included with local forecasts if temperatures are likely to come within record values, or if there's an imminent run of very hot or humid weather.

They meant people should consider precautions like staying hydrated and under shade, check in on vulnerable people and children, and look after pets and livestock.

"What we're looking to alert on is extreme or near record heat, say Christchurch being about to hit 39C or 40C - something beyond the peak temperatures that occur each summer," said MetService meteorologist Georgina Griffiths, who's working on the project with colleagues from Waikato University and ESR.

Another example was the unbearably sticky weather that Auckland just sweltered through, with a string of days with high temperatures and humidity.

"It's about considering the impact that heat has on people; I like my heat, but last week in Auckland was quite hard to deal with."

The town and city-specific warnings reflected that "extreme" heat could be a relative concept.

"The thresholds for the alerts are localised to the area in question - the threshold for Northland or Gisborne will differ from that used in cooler areas, such as Westland," University of Waikato climate scientist Dr Luke Harrington said.

"Thresholds to trigger alerts have been set very high, in part to 'future proof' this type of alerting against a background of continued warming due to climate change."

Woman drinking water in summer sunlight

Alerts would beem people should consider precautions like staying hydrated and under shade, check in on vulnerable people and children, and look after pets and livestock. Photo: 123rf

A recent synthesis led by Harrington showed the hottest days of the year have warmed by more than half a degree over the last 20 years for many populated regions of the country - a rate exceeding average annual changes across the country.

Global research has also shown the many health risks that could come with temperatures people weren't acclimatised to.

Sudden shifts could disrupt our body's normal biological cycle, with wide-ranging implications for our mental, physical and emotional state.

Other risk factors made some people more vulnerable: such as being very young or very old, obese or suffering from heart disease or poor circulation.

In already hot parts of the world, there's concern that climate change could be pushing conditions to extremes and making areas unliveable.

And despite its relatively cool and temperate climate, New Zealand isn't immune to extreme heat.

By the end of the century, if greenhouse gas emission rises continue to track at current levels, many regions would be recording more than 80 days a year with peaks above 25C, compared with between 20 and 40 days now.

Sydney at sunset.

Other countries like Australia and the UK already have an extreme heat alert system in place. Photo: 123rf/ Andrey Moisseyev

In previous research, however, Harrington has found flaws with that 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.

To define smarter thresholds for the 44 locations in their new trial, the team drew on nearly three decades of daily maximum temperature, humidity and wind data.

"These alerts are for extreme heat and we'd only expect to use them occasionally," Griffiths said.

"How often the alerts are issued, of course, depends on the type of summer we get."

While New Zealand had recently seen a string of record or near record summers, with plenty of moisture in the ground ahead of our warmest weeks of the season, the country wasn't starting off as dry as last year.

"The first week of December was cooler than usual, but La Niña temperatures are kicking in, producing above average summer temperatures, overall," Griffiths said.

The North Island locations covered by the trial are Kaitaia, Paihia and Russell, Whangarei, Dargaville, Auckland, Whitianga, Thames, Hamilton, Tokoroa, Te Kuiti, Tauranga, Whakatane, Rotorua, Taupo, Taumarunui, Gisborne, Napier and Hastings, Dannevirke, Masterton, New Plymouth, Whanganui, Palmerston North, Levin, Paraparaumu and Wellington.

In the south, the pilot will cover Motueka, Nelson, Reefton, Westport, Greymouth & Hokitika, Blenheim, Kaikoura, Christchurch, Ashburton, Timaru, Oamaru, Dunedin, Alexandra, Gore, Invercargill, Mount Cook, Wanaka, Queenstown and Milford Sound.

- This story was first published in the NZ Herald

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