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Is climate change to blame for the summer washout?

Days of intense rain will put a dampener on summer events, festivals and get-togethers.  (Photo file)

AIMAN AMERUL MUNER/Stuff

Days of intense rain will put a dampener on summer events, festivals and get-togethers. (Photo file)

As you pack up your sodden tent or cancel the weekend barbecue, you may curse the changing climate for the intensive downpours. But is global warming responsible for the weather woes?

More than a month’s worth of rain has fallen on Northland and Coromandel – with more to come.

Climate change makes extreme rain even more likely. But weather experts said the current forecast is a combination of many factors, including human-made greenhouse pollution.

One finger-pointed a high-pressure system – which first brought warm, sunny weather in the run-up to New Year’s Eve.

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Metservice forecaster David Miller said the high is now meandering across the Pacific to the east of Aotearoa.

If fast-moving weather moves in from the west, this type of slow-moving high can create a “squash zone”, he said. “Because the high has been parked to the east of New Zealand, it hasn’t let this tropical air go.”

This pattern over New Zealand concentrated rainfall. These rainy patches of air will “be sitting there for the next few days”, he added.

This set-up – high pressure to the east of Aotearoa and low pressure to the north-west – is “quite common” during La Niña years, Miller said.

Bringing moist conditions to the north and east of the country, La Niña is the opposite climate pattern to El Niño, which is famous for causing drought in eastern areas.

The rain-bearing low came from the subtropics, although it was never classified as a tropical cyclone, Miller said.

Instead, it was generated by a regular atmospheric phenomenon (known as the Madden-Julian Oscillation). Regularly, a patch of wet air and wind forms in the Indian Ocean, builds up over the seas surrounding Indonesia and moves into the Pacific Ocean.

“It makes the tropics more active, adding more fuel,” he said.

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Miller couldn’t confidently say climate change is or isn’t a factor in this week’s wild weather.

“You’d have to do more research on that,” he added. “But La Niña and the Madden-Julian Oscillation are the main drivers for this particular event.”

Overall, heating from climate pollution has already caused “unprecedented” hot spells plus heavier rain, according to the world’s climate scientists.

Average global temperatures are about 1.2C warmer than the pre-industrial era. The mercury could reach 1.5C of warming in the coming years.

The latest report from the Intergovernmental Panel on Climate Change warned every fraction of a degree of extra heat will cause more extreme heat waves, heavy rain, drought and sea level rise. Tropical cyclones and wildfires are also expected to worsen.

Niwa meteorologist Chris Brandolino​, who works with his organization’s climate scientists, said climate change leaves “a hand or footprint” on every weather event. “The question is: how big is said handprint.”

It takes “a bit of time” to determine the size of the contribution for each event, he warned.

But generally speaking, warmer air is likely to hold more water vapor, meaning a storm is capable of producing heavier downpours. “For every 1C of warmth, there’s roughly an 8 to 10% increase in rainfall,” he said.

People should expect more of this week’s weather.

As the atmosphere warms, rain will increasingly arrive in intense bursts, separated by drier periods, Brandolino said.

“I call it binge rainfall. Like Netflix: you’re watching the same content – but are you squeezing that in two days or stretching it out over two months? It’s a similar thing with rainfall.”

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