Heatwaves can kill, there will be more of them, and district health boards, councils and businesses need to develop health plans to manage their effects, the Ministry of Health says.
Many countries already had heat health plans — including generally cooler nations such as Britain — but New Zealand did not, the ministry said.
New Zealand did not even have a formal definition of "heatwave" — although a guideline report issued by the ministry at the weekend used a World Meteorological Organisation definition, of marked unusual hot weather persisting for at least two consecutive days during the hot part of the year.
Australia is now experiencing a record-breaking heatwave. Noona, in western New South Wales, made history on Friday with a highest minimum temperature of 35.9degC, and maximum temperatures have neared 50degC in some places.
The weather patterns driving that heatwave have affected New Zealand’s weather, bringing strong winds and temperatures in the high 20s.
The South has recent experience of heatwave conditions: last year, a series of scorching days led to the temperature in Alexandra reaching 38.7degC on January 30 — the 12th-highest temperature recorded in New Zealand — and records being set throughout the region.
The recently issued Niwa annual climate review said last January was the hottest month recorded in New Zealand, and 2018 was New Zealand’s equal-second warmest year on record.
"Because effects of heat are associated with relative rather than absolute temperatures, even in New Zealand’s temperate climate people can experience negative health effects with modest increases in seasonal temperature," the ministry said.
"Climate change is predicted to cause both average and maximum temperatures to rise and the number of hot days experienced in New Zealand is expected to increase."
Heatwaves are not recognised as a potentially significant hazard in the national civil defence plan, but weather incidents are recognised in local and regional plans.
The report recommended local government and district health boards develop heat health plans, and integrate those with existing emergency management plans.
New Zealand needed to develop appropriate thresholds for each region, based on demonstrated risks to human health, and should consider setting a temperatures which would trigger a warning, as Australia and England do, the report said.
No weather warnings about extremes of temperature are currently issued in New Zealand, although a system may be developed in the future.
"However, by recognising the early signs of heatwaves and their own individual risk factors, organisations can prepare for such events and in this way reduce the risks to human health," the report said.
Heatwaves could trigger surges in rashes, cramps, sunburn and heat exhaustion.
At worst, heatstroke and sunstroke — the body temperature exceeding 39.4degC — could cause the body’s thermoregulation system to fail, with potentially fatal consequences.
The old, young, homeless, ill, and alcohol and/or drug dependent were most vulnerable to heat-related conditions, the report said.
As well as health, proper monitoring of heatwave conditions could benefit transport, electricity and water providers and environmental planners.
