Climate change: Hamilton’s rare February heat streak could happen most summers by 2070

• Over a sweltering 15 days last month, maximum temperatures in Hamilton never fell below 27C.
• It was a once-in-a-decade event in today’s climate – but scientists calculate it could be occurring in three of four summers by 2070.
• They warn cities and the primary sector need to prepare now for a hotter future.

An extraordinary heat streak that brought Hamilton two weeks of sweltering temperatures could be playing out most summers within decades, scientists have calculated.

Over February, Hamilton’s maximum temperatures average around 25C: yet they never dropped below 27C over a 15-day heatwave early last month.

Among city residents who endured the unusual run of hot weather were University of Waikato climate change researchers Dr Luke Harrington and Hamish Lewis.

They turned to climate data to find the streak was indeed exceptional – a one-in-10-year event in today’s climate – but by 2070, such multi-week episodes could be playing out in Hamilton every three in four summers.

Their analysis, based on high-resolution models and local climate projections, indicated for every degree of warming in New Zealand’s annual mean temperature, the hottest 15-day spell in a Hamilton summer would intensify by around 1.4C.

By 2070, these extreme spells could be up to 2C hotter than today’s equivalent – and as early as the 2050s, Hamilton and surrounding regions could be enduring weeks of temperatures exceeding 30C.

Their study found while human-driven climate change was the main driver of these escalating heat events, natural climate variability still had the potential to produce record-shattering temperatures.

Harrington said while the numbers were specific to Hamilton, many regions were increasingly likely to see extended periods of high temperatures as the planet continued to warm.

Over February, Hamilton’s maximum temperatures average around 25C: yet they never dropped below 27C over a 15-day heatwave early last month. Image / MetService

That posed clear implications for human health: something that recently prompted MetService to begin issuing summer heat alerts.

“The biggest concern I have is for the aged care sector, particularly given how rapidly our population is ageing,” Harrington said.

“We should have an upper limit on allowable indoor temperatures in aged care facilities specified in the Building Code – the fact that we don’t baffles me.”

Seasonal workers in the horticulture sector would also find conditions increasingly challenging, he said, suggesting employers adjust working hours and break times.

“Heat stress is already a significant issue for both dairy and sheep and beef farming in many parts of the country, in terms of ... animal welfare but also milk production,” he said.

“That’s only going to get worse, so existing efforts looking at livestock adaptation needs to continue apace.

“That includes the integration of the slick gene to improve heat tolerance in dairy cattle – as well as exploring the potential for no-wool sheep in some regions.”

Local councils could also plan to set up cooling shelters or misting fountains in parks during the peak of the summer, Harrington said.

While New Zealand remained “far behind the rest of the world” in acknowledging the risk of extreme heat, he was encouraged awareness was at least slowly growing.

“My fear is that we remain complacent until we have a wake-up call in the form of a severe heatwave event: something like Canterbury in 1973, Europe in 2003, India in 2015 or British Columbia in 2021.”

Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.

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