What happens when we hit 40C

It’s getting hotter everywhere and New Zealand isn’t immune to devastating heatwaves. Elijah Hills asks what would happen if we hit 40C.

‘‘We haven’t had 40C in the North Island yet, but I wouldn’t consider that to be unlikely.’’ Nava Fedaeff, Niwa

Wrapped up for the middle of winter, Kiwis have watched temperatures soar to 40C in Europe and North America leading to deaths, fires, failed crops and widespread drought.

But as the days start to get longer, Niwa weather forecaster Nava Fedaeff says she wouldn’t be surprised if New Zealand had its own record-breaking heatwaves this summer.

‘‘It’s not just a one-off, two or three days a year. It’s something that could be happening every other week or something like that.’’

The hottest temperature yet recorded in New Zealand was 42.4C, on February 7, 1973 in the North Canterbury town of Rangiora.

Roads melted, railways buckled, workers walked off the job, thousands flocked to beaches and pools, schools closed and firefighters scrambled to battle blazes across the region.

It hasn’t been terribly different in the UK, enduring its hottest summer ever. In one three-day period as many as 1000 deaths were directly attributable to the heat.

Fires broke out in forests, parks and residential areas, stretching firefighting resources so thin even small incidents quickly grew out of control.

Although electric fan and icecream shortages tend to hit headlines in New Zealand when the mercury climbs, high heat has a darker side than just requiring a trip to the beach to cool off.

Everything from organs to enzymes can shut down when a person’s core temperature gets too high and this can lead to major kidney and heart problems, and even brain damage.

France has experienced this already. In 2003, its heat-related death toll hit 15,000. These were mostly older people, often living alone.

It was so bad the French government created the National Heat Wave Plan which outlined who should do what when temperatures reach certain levels. It appears to have worked – deaths during the recent heatwave have been relatively low in number.

Up until this year the UK had dodged the worst of the annual European scorchers and so it has not taken equivalent action.

A major issue to emerge during the current heatwave is the way UK homes have for generations been designed to retain heat, to make cold winters bearable. As a result, a huge number of people cannot cool their homes to safe levels.

It is a similar situation to New Zealand, where a Stats NZ survey showed more than a third of homes are too warm in summer.

At best this can make it tough to sleep, but at worst, being too hot puts a person’s body under significant stress that can exacerbate existing conditions and it is the elderly and very young who are most vulnerable.

New Zealand’s hottest climates are not shared evenly around the country with the east generally hotter and dryer than the west.

The highest temperatures can be attributed to something known as the Fo¨hn effect, where hot northwesterly winds arriving from Australia get even hotter and lose moisture crossing the Southern Alps.

It’s the reason why areas such as Canterbury and Otago can become so scorching.

The effect also occurs to a lesser extent in areas such as Gisborne, Hawke’s Bay and Wairarapa in the North

Island.

‘‘We haven’t had 40C in the North Island yet, but I wouldn’t consider that to be unlikely,’’

Fedaeff says.

New Zealand’s most recent 40-plus day recorded was at Timaru Airport in 2011.

With no mountains to create the Fo¨hn effect and large bodies of water nearby to act as heat sinks, cities such as Wellington and Auckland, and many other areas of the country, are not likely to experience such extreme heat – but that doesn’t mean they won’t still get record hot conditions.

When it comes to roads, Kiwis could face more than just the odd jandal stuck to the pavement during heatwaves.

Across Europe and parts of North America, melted asphalt has been running off the roads and encasing car tyres, making travel impossible.

To enable the famous Tour de France cycle race to continue, organisers drove in front of riders spraying tens of thousands of litres of cold water on the road to keep it rideable.

Changing climate means roads are being forced to endure a wider range of temperatures and conditions, University of Canterbury civil engineering professor

Mofreh Saleh says.

‘‘If you’re measuring the air (and it’s) 45C, you would expect the pavement (to be) probably 10-15C (above that) or even higher, the pavement itself could reach easily 60C.

‘‘So basically, you can cook your egg outside on the road.’’

If we want our roads to cope with these conditions, and there really isn’t much choice, the cost will soar with the temperature, he says.

The type and timing of any 40C heatwave will play a big factor on how New Zealand’s flora and fauna are affected.

Generally, dry heat has a greater effect on plants than more humid conditions, Plant & Food Research principal scientist Grant Thorp says.

Crops grown in Otago and on the North Island’s East Coast, such as apples and stonefruit, tend to do better in dry heat than avocados or kiwifruit.

Even so, apples still require cool nights to get their red colour – without which they stay green or go yellow.

Kiwifruit, which makes up about 32% of New Zealand’s total horticultural export revenue, could be hard hit by high temperatures.

Thorp studied golden kiwifruit in California during 40C-plus weather and recalled seeing fruit which stayed green rather than turning gold.

‘‘... and then they shrivelled, and they ended up being all tough and rubbery – like a jandal, we used to say.’’

Any reduction in the quantity of fruit and vegetables harvested will inevitably lead to an increase in price. New Zealanders may have to get used to paying more for the fruit and vegetables than they are used to. On the other hand, fruit and vegetables that thrive in the hot conditions may become cheaper.

Although high air temperatures don’t always translate to high temperatures in rivers, lakes and the sea, our waterways are already feeling the effects of climate change.

In 2020, hundreds of thousands of mussels were cooked to death on a Northland beach, while in summer, salmon in the Marlborough Sounds died at a faster rate than ever.

Cawthron Institute freshwater ecologist Laura Kelly says variation in water temperatures can affect the invertebrates that provide native fish with food.

Most native fish, aside from some eels, also have a preferred water temperature of less than 20C – going above this affects their ability to forage and feed.

‘‘Once you start getting into that 30C to 35C water temperature range, you’re looking at the upper limit where they will start dying.’’

Providing shade through tree planting and looking after the health of waterways can help negate some of these effects, she says.

Cawthron Institute marine ecologist Kirsty Smith says higher temperatures can boost toxinproducing species and algal blooms.

Algal blooms have been found to affect not only shellfish health, but also the health of humans who consume shellfish taken from a bloom area.

Extreme heat will also affect our forests.

A Ministry for Primary Industries report says fire severity is likely to rise significantly in the east and south of the South Island, especially in coastal Otago and Marlborough and south-eastern Southland, as well as on the west of the North Island, particularly Whanganui.

Many of these areas have already seen the effects of fire, such as 2017’s devastating Port Hills blaze which burnt the equivalent of more than 1600 rugby fields and claimed the life of one firefighter.

In Tasman in 2019, a spark thrown up by a tractor ploughing a rocky field turned into the country’s biggest aerial firefight on record and burnt through the equivalent of 2300 rugby fields.

These fires are part of a global phenomenon breaking forest-fire records every summer. The 2021 Dixie wildfire in Northern California burned for more than two months and was the largest singlesource wildfire in the state’s history, costing US$637.4 million (NZ$989m) to fight.

The ‘‘monster’’ wildfire currently raging near Bordeaux in France had forced 10,000 residents to flee already as of yesterday.

‘‘It’s an ogre, it’s a monster,’’ firefighter representative Gregory Allione told France’s RTL Radio.

Such massive fires can also have unexpected consequences for the global ecosystem. Smoke from Australia’s 2019-20 bushfires, for instance, stimulated algal blooms so big they could be seen from space.

Despite global heating, not every part of New Zealand will experience dryer conditions. Traditionally wet areas such as the West Coast of the South Island and Taranaki are projected to receive increased rainfall – reducing their fire risk.

New Zealand isn’t standing still in the face of such rapidly changing conditions.

The Government this year released New Zealand’s first National Adaptation Plan, a 193-page document outlining how the country can become more resilient in the face of a changing climate.

The document explores everything from the threat of severe droughts to drinking water and electricity generation to how we can increase the resilience of everything from the natural environment to communities and the economy.

University of Waikato senior lecturer in climate change, Luke Harrington, says the plan is a timely reminder that climate change is about more than just sea-level rise.

‘‘We need to contend with the reality of more severe and frequent droughts, widespread increases in the intensity of extreme rainfall events and rapidly changing risks associated with extreme heat.

‘‘Many of the impacts of climate change can be reduced by ensuring our responses are people-focused: Understanding who is exposed and how to bolster their resilience to worsening hazards.’’

Harrington says it is the very old, the very young, and those with chronic health conditions who need targeted assistance when extreme weather events occur.

‘‘Yes, urban greening can help to mitigate the effects of extreme heat in cities, but this will only work alongside early warning systems, pop-up cooling centres which are free and easy to access, and monitoring plans which are tailored to our most vulnerable friends and whānau.’’