From the archives: In 2021, Paul Gorman wrote about a subject likely to fascinate most of us: where are you most at risk of lightning strikes? While we are no longer experiencing a La Niña weather pattern – we’re currently contending with El Niño – the story contains pertinent warnings and information especially as the country moves into autumn and the chance of stormy weather increases.
Sparks zapped between his metal fillings and leapt from his horse’s shoes, confirming to James Falloon that he had narrowly escaped a lightning strike.
Just 10m or so behind him fellow Northland Hunt participant Roger McGill and his horse Jaffa lay dead.
Falloon, a former Canadian cowboy and now a semi-retired farmer in the Wairarapa, said thunder was rumbling to the north near Dargaville when the hunt began just before midday on April 15 2008.
“I’d trotted past him but none of us saw the flash or heard the boom. But it was like a force went through us. Blue sparks were coming off the shoes of the horse. They were as big as your fingers. Sparks were going off in my mouth.
“My horse bolted and I turned around and Roger was lying about 5m away from his horse. They were both dead.” McGill, who with his wife and two young sons lived on a Waitoki lifestyle block north of Auckland, was well known in theatre circles in the city and was a founding director of Theatre Corporate.
Experts say on average there is about a death a decade in New Zealand from being hit by lightning, about a quarter of those dying outright. Several farm animals are also killed by lightning each year.
Lightning can be between 100 million and 1 billion volts, compared with the 230-240V of a New Zealand household power supply.
Lightning researcher Kerryn Hawke says the weather pattern that April 2008 day was dominated by a warm, moist northerly airflow. “That provides a good environment for convective activity and the hills around Northland can provide that extra oomph that may be needed to get the air moving up and producing convective clouds.
“One thing that stood out to me in the coverage is that the fatality occurred on top of a hill and while riding a horse. Unfortunately that would have increased the risk of a lightning strike as the more elevated you are compared with your surroundings the greater the risk.”
She says reported injuries from lightning are more frequent. Two men were struck in separate incidents in June 2013 near Cambridge in the Waikato, as were two fisheries officers on patrol close to Gisborne in December of that year.
As fisheries officer Martin Williams told RNZ last year, it felt like he’d been “walloped by something, or you were inside a bass speaker”.
After a split-second sensation of burning heat, he felt time had dilated and the world had gone dim.
“It was like someone actually turned down the brilliance on your TV … It was like you’d shifted into the twilight zone.”
Once he realised he’d been hit by lightning and was still alive, “time caught up and you just felt a tingling, like pins and needles throughout your whole body. It actually felt like you had ants crawling all over you.”
That “bolt from the blue” is what keeps Hawke awake at night. A brewing thunderstorm 20km away might be out of sight, out of mind, for most. But she knows that, even at that distance, people are in danger from positively charged lightning firing out from the top of the cloud. And New Zealand has proportionately more positively charged lightning than many other countries.
“Positively charged lightning carries, on average, a stronger charge than the more common negatively charged lightning and tends to be more destructive. It can travel through the air and hit the ground at a location remote from the storm so it is colloquially the ‘bolt from the blue’.
“From a public-health and safety point of view those are the ones that are the most dangerous – not only because they have more charge but also because people are less aware. If it’s pouring with rain people will think, ‘let’s get in out of this rain’, but in this case they could be out doing their thing thinking they are safe.”
Of the lightning that hits the ground (not all does), about three in every 10 strikes in New Zealand are
positive, Hawke says.
That means Kiwis are more at risk of being struck by lightning from distant storms than people in some other countries, despite New Zealand having less lightning overall than the US, Australia and in the tropics.
Lightning is caused by a separation of electrical charge at different heights of a thundercloud and the charge trying to equalise that.
Pummelling hail
The spark of lightning and the crack, boom and rumble of thunder have not been far away this summer, largely thanks to the La Niña weather pattern dragging warm and very moist, often subtropical, air across the country.
Baking in Perth’s summer heat, the Murdoch University associate lecturer is intimately acquainted with our thunderstorms – their icy anvil clouds with bubbling cauliflower turrets and inky black-purple bruised-looking bases. Not to mention the pummelling hail, torrential rain and even tornadoes that can accompany them.
Hawke grew up in Hawke’s Bay – “quite a place for thunderstorms” – and compiled New Zealand’s first lightning climatology as part of her doctorate in environmental studies at the University of Canterbury.
Using data from 2001 to 2012, supplied by MetService from Transpower’s lightning-detection network, she investigated how weather patterns and atmospheric processes influence patterns of lightning around the country.
She says there were a lot of new findings in her thesis – “not hard when no New Zealand lightning climatology had been done before” – but she was especially fascinated to discover how some parts of the country had a greater risk of being struck by the more dangerous positively charged lightning than other places.
“Wellington, the West Coast and Southland have the highest proportion of positive lightning because of the way the convection, which produces the lightning, is caused. This tends to be from the passage of fronts.
“Wellington, for example, doesn’t have a huge number of thunderstorms, but when it does, you’ll often see on the news that they’ve had a lightning strike. A good example was when the Phil Price Zephyrometer in Evans Bay was hit in August 2014.”
The peak current for positively charged lightning during the years Hawke studied was 508 kiloamps (508,000A), recorded on August 11 2008, in the Ikawhenua Range in the Bay of Plenty.
Despite the strength of that charge, lightning is far less likely to start wildfires in New Zealand than in Australia and parts of the US, such as California, Hawke says. “Researchers at Scion have found that only about 0.1% of all New Zealand wildfires are caused by lightning, although there are a lot of fires where the cause is unknown.
“One of the reasons for this is that ‘dry lightning’ [without rain] is much less common in New Zealand than Australia, where precipitation from thunderstorms often evaporates before reaching the ground because it’s hot and very dry.
“Dry lightning does not happen nearly as readily in New Zealand because it’s cooler and being surrounded by oceans there is generally more moisture available. Rain either before, during or after a lightning strike can be enough to either directly extinguish a lightning-ignited fire before it takes hold or damp down the fuel so that it doesn’t catch fire.”
Risks underestimated
Hawke says people often don’t make safe decisions during thunderstorms because they lack awareness of lightning’s power to injure and kill.
She recalls while researching in Christchurch driving past a school where a sports day was in progress “and all the kids, teachers and parents were out there and the sky was that kind of purply-black colour of an imminent thunderstorm. I thought, ‘People just don’t understand what the dangers are.’ And then lightning hit a tree near Princess Margaret Hospital.”
Hugely damaging hailstorms such as that experienced around Motueka on Boxing Day 2020 often accompany the most vigorous thunder and lightning activity, she says. It’s all due to the size of the cloud and the intensity of the up- and downdrafts within it. “Hail is produced in a cumulonimbus cloud – the same cloud that produces lightning.”
As the climate warms, with increased moisture in the air, there is a chance of more and bigger thunderclouds. “The vast majority of research looking into lightning projections in future is saying lightning is predicted to increase, especially in the mid-latitudes. If there’s more lightning, there’s going to be more of that positively charged lightning.”
Local hotspots
This summer’s La Niña has given a hint of that increased storminess, she says. “There are warmer oceans in the La Niña phase, and you tend to get more warm moist northeasterly winds coming in over the country than normal so you have more instability. The storms over the central North Island this summer are a fantastic example of that.”
So where are the lightning hotspots around the country? Hawke says the South Island’s West Coast has by far the most lightning, with little difference between it happening during the day or at night. It is more frequent in autumn and winter as lightning is associated with cold fronts. The region also has a higher chance of positively charged lightning.
Lightning in the east of both islands is mostly an afternoon or evening occurrence in the warmer months triggered by southerly changes and local wind patterns.
Elsewhere in the North Island, lightning is often associated with light winds and sunny summer afternoons and evenings, allowing thunderclouds to build up over the warm land as sea breezes converge. It is also associated with fronts arriving from the west or, in Wellington, from the west and south.
“Lightning is lazy,” Hawke says. “It will try to reach the highest point so it can dissipate its charge the fastest.” That makes Auckland’s Sky Tower a prime target. “Because lightning tries to find the shortest path to the ground as possible – it takes a lot of effort for electricity to move through air – tall buildings do tend to get hit by lightning more than smaller buildings in the vicinity.”
In June 2000 the Sky Tower was hit 16 times by lightning in 30 minutes, destroying MetService instruments and knocking out radio and internet transmitters.
A lightning conductor from Australia was installed, with a gold-plated ball and a spike, to attract lightning and send the electric current into steel bars inside the tower and down to the earth. “Wind turbines and power pylons are other structures that are often hit by lightning, which is why Transpower owns the New Zealand lightning-detection network,” Hawke says.
There are lightning-protection standards that builders have to follow and if a building is assessed as needing protection this would be designed into the building.
Hawke says as well as the obvious risk of fire damage to a building struck by lightning, it can also destroy wires and pipes.
“A common insurance claim after a lightning event is for fried electrical equipment. The strike may not have hit the dwelling – in fact, it’s more common to get electrical-equipment damage by lightning striking, say, a nearby power pole, with the surge travelling through the wires and into the house. That’s why I always unplug my computer, TV and so on when there’s a thunderstorm.”
Lightning strikes on aircraft are not uncommon either, Hawke says. At least three times last year planes had to divert or return to the airport after being hit by lightning. In August an Auckland to Queenstown flight was diverted to Christchurch and in November a plane bound for Hamilton from Wellington landed at Auckland. In December a flight heading for Wellington had to return to Invercargill after being struck soon after takeoff.
“Much more lightning stays in the air than reaches the ground so lightning strikes on planes are not uncommon, especially when the plane is climbing or descending through clouds,” Hawke says. Protection systems channel lightning away from the cabin and essential aircraft systems, meaning significant damage is rare.
Hawke is keen to make her study more comprehensive by including lightning data for the years since 2012 if she can obtain it from MetService. She is also pushing for greater public awareness of lightning’s risks.
“Internationally, especially in developed countries, a high proportion of lightning fatalities occur while doing sports – fishing, boating and golf are high-risk – and men are much more likely to be killed than women.”
Between 2006 and 2016 352 people were killed by lightning in the US, almost two-thirds of them involved in outdoor leisure activities. Men accounted for 79% of the deaths.
“The only safe place in a thunderstorm is indoors in a proper building. So the best way to stay safe is to check the weather and if a thunderstorm is forecast change your outdoor plans.”
This story first appeared in the NZ Listener’s March 13 – 19, 2021 edition.
