What will be our first El Niño summer since 2016 is now shaping up to be one of the most intense in eight decades - raising the risk of drought on the North Island's East Coast. Photo / Andrew Bonallack
An El Niño climate pattern anticipated to be among the strongest in 80 years has forecasters looking ahead to a potentially unprecedented summer for parts of New Zealand. Science reporter Jamie Morton explores the four big trends they’ll be watching closely.
If you’re already tired of the pesky westerly winds that’ve been blowing hard these past few weeks, get used to it – summer’s likely to be even windier for New Zealand.
“In my 30 years of looking at forecast summer patterns, I haven’t seen one this westerly that I can remember,” MetService’s Georgina Griffiths said.
What will be our first El Niño summer since 2016 is now shaping up to be one of the most intense in eight decades.
Forecasters have already been turning to some of the most memorable El Niño events that’ve played out here – notably the dramatic summers of 1982-83 and 1997-98 – and a repeat only meant stronger, more frequent westerlies as the warm season approached.
This classic El Niño calling card owed to the way the big climate driver helped to place high pressure to the north of New Zealand and low to our south – like two spinning cogs of a wheel constantly steering westerly flows toward us.
It meant different weather for different places: those in the South Island’s West Coast could expect more rain bands and fronts, while, in regions like Hawke’s Bay, Gisborne, Canterbury and eastern Marlborough, those winds would instead arrive warm and stripped of moisture.
That constant wind, however, would be felt everywhere, Griffiths said – and El Niño wouldn’t be the only factor behind it.
Climatologists were expecting a key indicator of storminess in the oceans deep below New Zealand, called the Southern Annular Mode, to run unusually negative over coming months.
“So, while we have a really intense El Niño in play, we’re also likely to have a very stormy Southern Ocean over summer – and that will just amplify that westerly pattern,” Griffiths said.
For Kiwis in centres like Wellington, who enjoyed relatively pleasant summers over the last few years of La Niña, the contrast would be especially stark.
“The big headline is that this summer looks to be absolutely different from what we experienced last year, which was a bummer-summer in the north, and a great summer in the south,” she said.
“The reverse is true for what we’ve got coming.”
Niwa forecaster Ben Noll had little doubt the dominant westerlies would be a talking point among Kiwis.
“They’re going to grow quite annoying to people this summer, especially when it comes to cancelled flights or holidaymaking.”
After some incredible wind speeds this month – a 246km/h gust measured at Cape Turnagain on September 17 came close to setting a new national record – Noll saw plenty more opportunity for powerful gales.
“We’re looking right to the end of summer – and the outlook for February looks very similar to October and November,” Noll said.
“In terms of wind intensity, it’s pretty unrelenting.”
One consolation was that choppier seas would make it harder for marine heatwaves – which have had major impacts in and above water over the last few years - to form around our shores this summer.
Yet, there’d be more than enough other drivers in the mix to wreak their own havoc.
We’ve already seen those gusty westerlies tear off roofs and bring down trees and powerlines – but arguably their more serious impact has been occurring below ground.
“Soil moisture for Canterbury just went from full to about empty in only two weeks of westerlies in the first half of September – it’s happened so quickly that it’s surprised me,” Griffiths said.
Adding to this was the likelihood of much less long-term rainfall in hot-spot areas like the North Island’s East Coast, despite a deluge forecast for Tairawhiti for the next 48 hours.
Hawke’s Bay, which ended last summer as one of the soggiest parts of the country, received just half its average rainfall for August – and only about 5 per cent of normal over the first half of September.
“We’re already seeing the flavour of the summer with these westerlies and that soil moisture just absolutely plummet,” Griffiths said.
WeatherWatch’s Philip Duncan had been similarly taken aback by the speed of that change.
“As someone on Twitter said to me recently, El Niño is bringing a hair-drier effect to the eastern side of New Zealand,” he said.
“In coming months that is likely to be more widespread and spread further over the North Island and upper South Island.”
Griffiths said El Niño didn’t necessarily mean all our eastern regions with normally dry summers would feel the effect.
“It may actually not be a case of every day being sunny and dry for eastern places like South Canterbury, Marlborough and Nelson – and the signal for Southland, Central Otago, and obviously the West Coast of the South Island is extremely wet, cloudy and horrible.”
Noll was similarly closely watching soil moisture levels, which have also tumbled in eastern Northland, Gisborne, Wairarapa, Marlborough and parts of Canterbury.
What water this coming storm delivered to the East Coast could be quickly stripped from the ground by warm westerlies.
“If we look at the climate models for spring and into summer, they’re producing odds of below normal rainfall in the north and east of both islands in the 50 to 70 per cent range, which is a very high level of confidence.”
Noll anticipated another big-picture climate driver – a positive phase of the Indian Ocean Dipole – to work in tandem with El Niño to enhance those regional patterns.
Though it’d be premature to pick all-out drought for some areas this far out from summer, there were enough “pieces on the table” in the long-range modelling to sound warning bells for farmers.
“There’s a real concern here, especially when you’ve got low prices for our sheep at the moment, along with high interest rates,” Gisborne sheep and beef farmer Toby Williams said.
Farmers were preparing for a drier season by bringing weaning forward and marking dates to off-load stock by, if little rainfall came.
“The one thing we’re not concerned about right now is our aquifers – our springs are still running high, so water for stock isn’t going to be an issue going into summer – but feed potentially will be, and grass is running pretty tight,” said Williams, who serves as Federated Farmers’ meat and wool chairman.
Among old hands, thoughts of disastrous El Niño summers like 1997-98, which cost hundreds of millions of dollars, loomed large.
“Some of those horror memories, you try to suppress them and hope that it’s not going to be like that – but if you’ve farmed through them, then you know what the trigger points are,” he said.
“The key thing is having those conversations with your neighbours and the people around you, and keeping your bank manager involved.”
The Ministry for Primary Industries’ acting director of rural communities and farming support, Andrew Curtis, said it was possible drier conditions could set in earlier - and linger longer.
That could spell water restrictions and less crop growth and pasture cover – although some sectors, like wine and fruit crops, might stand to benefit.
Curtis said the ministry was working closely with Niwa – with which it’s launched a drought forecasting tool – and with farmers, through services like its new regionally-based On Farm Support programme.
“Should there be significant impacts from a drought, MPI can consider various forms of support working with other agencies including Inland Revenue and Work and Income.”
Fortunately for Aucklanders, there wasn’t any sign of a looming repeat of the 2019-20 summer’s big water shortage, with local dams sitting at more than 99 per cent capacity, WaterCare’s head of water value Andrew Mercer said.
“Our own modelling indicates our total dam storage level is likely to be in a good position by the end of summer and as we head into autumn – even if we do face the extended dry periods forecasters are predicting.”
When the mercury climbed to 29.6C in Wairoa last week – a new September record for the North Island – locals were left wondering what those daytime extremes would look like four months from now.
Many of our most blistering historic temperatures – including the still-reigning 42.4C that Rangiora reached in February 1973 - have coincided with El Niño.
Only in 2023, Noll said, the pattern would be playing out with global warming’s tailwind.
“Even in the last decade, we’ve seen a number of years of warming since our last El Niño in 2015-16,” he said.
“So, when we get these hot dry air masses from Australia, they’re warmer than they would have been in the past – and all things being equal, you can really start to achieve some very high daytime extreme temperatures.
“Maybe a few months down the line, 30C might become 35C. It’s been a while since we hit 40C in this country, but there are higher odds for something like that to happen this year than there was in our last few summers.”
Griffiths had her eyes cast particularly on Hawke’s Bay and Gisborne – but also the eastern South Island, from Kaikoura down to Timaru – and said MetService’s heat alert system would kick in earlier this year.
“Those foehn westerlies are consistently forecast to have a real impact on temperatures in those eastern regions.”
Waikato University climate scientist Dr Luke Harrington said that, while El Niño’s presence didn’t guarantee record-breaking extremes in parts of the country this summer, “the risks are certainly elevated”.
Harrington also pointed back to that baking-hot 1972-73 summer, but also February 1998, which proved the month with the largest number of extreme hot spells for many of the North Island’s largest cities.
“There’s an open question about whether heat stress risks are greater during La Niña or El Niño events, but the reality is we should be expecting record-breaking heat to be occurring nearly every summer these days,” he said.
“That’s the consequence of global temperatures currently rising at such an unprecedented rate.”
Amid what was New Zealand’s warmest summer, climate change was found to have made a roughly 1C contribution to extreme heat observed in Southland on January 31, 2018.
“It was also about 10 times more likely that we witnessed such high temperatures in today’s climate relative to a world without climate change,” Harrington said.
“We’d expect these numbers to be a little higher again were we to look at any extreme heat events that might happen this summer, particularly in the North Island.”
With that extreme heat came potentially significant health risks for vulnerable people.
“It’s not people in their 20s or 30s holidaying at the beach that we’re worried about,” Harrington said.
“Rather, it is elderly people living in aged care facilities, seasonal workers who are outdoors during the hottest part of the day, and children under 5 who can’t regulate their body temperatures as effectively as adults.”
Hot, dry, blustery weather of course also spelt a headache for rural firefighters, who’ve been busy preparing for what threatened to be a disastrous fire season across most of New Zealand’s east coast.
Fire and Emergency NZ wildfire specialist Rory Renwick said conditions could prove similar to the 2019-20 season, when crews had to deal with more than 5700 blazes, and also 2002-3.
“We had a lot of wind-driven fires through Canterbury that summer and had to cycle crews from all around the country.”
In any case, he said the season was “definitely likely” to bring more days of extreme fire danger.
“When we talk about extreme fire danger, it means there’s a likelihood you’re going to get a fire of such intensity that even aircraft are not going to be able to stop it at the head of the fire,” Renwick said.
“They might be able to work around behind it to control it, but you’re talking about fires that are going to unstoppable until the weather changes or the fuel runs out – and this is quite a likelihood for many areas.”
Those predicted soaring temperatures – especially amid long dry spells of low humidity - also raised the risk.
“When you hear predictions for an extra degree or two of temperature here and there, it doesn’t sound that threatening – but when you get more of those, the number of days of extreme danger is going to be several times what the norm is,” he said.
“We also haven’t experienced that normal for the last few years – so this is going to be extremely different.”
Climate scientist Dr Nathanael Melia, who’s modelled wildfire risk decades into the future, summed up the picture: “To put it simply, it’s looking bad.”
Making predictions on seasonal timescales was notoriously difficult, but, if you only had September conditions to go on, “for the last 20 years, betting that 2023-2024 would see the worst wildfire weather might get you about even odds”.
Alongside El Niño, Melia, of Climate Prescience, saw another big risk factor this season: extra growth from record-wet conditions.
“The record wet going into El Niño to have two effects: firstly, the vegetation is going to go grow like it’s on Viagra over September and October,” he said.
“If this dries out, there is going to be heaps of available fuel. Secondly, we might expect some areas and vegetation types to take longer to dry out and get drought-stressed, if that record rain is still able to be accessed.
“This and the myriad [other climate drivers] means there’s a large element of uncertainty to exactly how it’s all going to unfold.”
Melia echoed officials’ calls to Kiwis ahead of summer: start thinking about fire danger now.
“Wildfires need ignition, in Aotearoa, ignition means people, this means that wildfire can occur essentially anywhere around us - not just in those regions that may have the most extreme risks.”
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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