Mega-flooding warning from top climate scientist: Have we had our last classic Kiwi summer?

“We’ve got to take stock and think about what we want the country to look like in another 50 years. Because the way it looks now is not going to be liveable.”

Three years ago, 16 people died in the Auckland floods and Cyclone Gabrielle.

The 2026 summer storms have seen slips destroy homes and cause major road damage, left tens of thousands of people without power and grounded dozens of domestic flights.

As Hawke’s Bay braced for wild weather late last week, a popular beachside campground was evacuated after a geotechnical assessment revealed the land above it was “highly unstable” and heavy rain could lead to a catastrophic landslide.

Renwick says what we have experienced over the past month is predicted to get worse across future summers.

Renwick – who in 2018 won the Prime Minister’s Science Prize for communication – said global warming is putting more moisture into the atmosphere.

While the frequency of storms won’t necessarily increase, the brutal intensity of downpours - and the damage - will.

“There’s no projection there will be more storms in future... but when they come, they are becoming more and more powerful. More rain, stronger winds.

“I actually can’t imagine what an even more pumped-up Cyclone Gabrielle would look like. I don’t really want to think about it.

“A Cyclone Gabrielle kind of storm in another 30 or 40 years ... you could have rainfall amounts that are 50% higher than we saw with that storm. Mega flooding everywhere, or anywhere a storm hits, terrible slips and deaths.

“That kind of thing you’d expect to be happening more often.”

Cyclone Gabrielle brought 546mm of rain when it struck Hawke’s Bay – the worst area impacted by the 2023 storm – including 501mm in 24 hours.

Half the region’s normal annual rainfall was recorded in a two-day period.

Last month, more than 270mm drenched Tauranga before the duo of fatal landslides at Mt Maunganui and Welcome Bay.

A 2024 United Nations report said the world’s temperature was set to rise by more than 3C by the turn of the century – spurred on partly by greenhouse gases – with warnings Earth would “plunge headlong into a climate disaster”.

Renwick says the so-called ‘Great Kiwi Summer’ uninterrupted by severe weather is something of a myth.

“The number of storms hasn’t really changed significantly over the last century or so,” he said.

“It’s not the case that we used to have glorious summers and now we don’t. We have had some really bad [summers].”

Going back to when records were first kept in the 1860s, parts of New Zealand have consistently been pummelled by ferocious weather events early in the year.

The Great Storm of 1868 caused extensive flooding nationwide, and sank numerous ships.

One hundred years on, the early-autumn Cyclone Giselle hammered the Wellington region and led to the sinking of the ferry Wahine, and the loss of 51 lives.

The past five decades have included the deadly Cyclone Bola that cut off access to the East Coast, successive summer storms in 1993 and 1994 that caused flooding in the South Island, a trio of summer storms that hit the Coromandel over three months in the summer of 1996-97 and repeated storms in Northland.

The storms have gradually become more potent, Renwick said.

“The rainfalls today are 10 or 20% worse than they were 10 years ago and they’ll be 20% worse in another 10 or 20 years,” he said.

The underlying factor behind that is that as the Earth warms, so too does the sea, which puts more water vapour into the air - especially in the summer months.

“You tend to get the heaviest rainfalls in the summer,” Renwick said.

“The nature of the storms in the winter is a bit different. Generally, because it’s colder, there’s less moisture in the air so the rainfall amounts are not as intense.”

It is a view shared by Earth Sciences New Zealand chief scientist Chris Brandolino.

Because New Zealand is an island nation, warmer ocean temperatures will have “an upward influence on our air temperature”, he said.

“That produces more water vapour,” Brandolino told the Herald.

“And water vapour is fuel for heavy rain.”

He said climate change was increasingly bringing extremes to the weather; including over summer.

“The extremes are accentuated,” he said.

Renwick – a Climate Change Commissioner from 2019-2024 – says amid growing scientific evidence and worsening storms, he would like to see action on climate change.

He sometimes feels he is “banging my head against a brick wall”.

Late last year he was critical of the Government’s moves to reduce a legislated target for cutting methane emissions.

He believes governments and industries around the world aren’t doing enough to tackle climate change by lowering greenhouse gases, which is a source of frustration for him as a scientist.

“I get a call from a reporter when there’s a storm, there’s a wee story on the news and then we’re back to the rugby and what’s happening with the Royal Family,” Renwick said.

“Collectively we’re just walking towards the end of the cliff.”

Earth Sciences NZ has completed detailed research into the potential impact on New Zealand if the temperature rises by 3C.

In a paper published late last year, it said up to 900,000 New Zealanders could be flooded in extreme storms.

It would also expose $288 billion in buildings and houses, 30,800km of roads and 29% of our national grid sites (including power substations) to flooding.

“It’d be great if the country could talk about what are we going to do in response to all of this?” Renwick said.

While parts of the country continue their storm clean-up, Earth Sciences NZ says more damaging weather could be coming.

Its February-April Seasonal Climate Outlook says during the next 10 weeks the risk of ex-tropical cyclones “may increase again”.

“Cyclone (TC) season indicates a normal or elevated risk for ex-TC interaction for New Zealand,” the outlook states.

“Although the season has been quiet so far, the peak risk for northern New Zealand is typically late summer and early autumn.”

Brandolino told the Herald that from mid-February, we enter “the apex of the tropical cyclone season in terms of things being active”.

He stressed the remnants of a tropical cyclone aren’t crucial to another soaking towards the end of summer.

The weather system that forcefully made its way down the North Island from late last week didn’t stem from a tropical cyclone.

“We don’t need a tropical cyclone to cause significant impacts,” he said.

Neil Reid is a Napier-based senior reporter who covers general news, features and sport. He joined the Herald in 2014 and has 34 years of newsroom experience.

Sign up to The Daily H, a free newsletter curated by our editors and delivered straight to your inbox every weekday.