Understanding just how wet it has been this winter

Monday, 22 August 2022

Prime Minister Jacinda Ardern visits Nelson to meet residents affected by the August floods and land slips. First published August 22.

The South Island is about to close out an extraordinarily wet winter in 2022, where flooding hit Christchurch, Otago, Nelson, and the West Coast.

Numerous rainfall and temperature records have been broken over the past three months, according to Ben Noll, a meteorologist at Niwa.

Nelson is the latest victim of bad weather, with flooding, evacuations and landslips in the past week. The region is expected to take years to recover.

Flooding around north Nelson and Glenduan in August.

Nelson Airport has seen 383mm of rain fall this month, Noll said, which is close to five times the 83.8mm the area would get during a typical August.

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* Nelson floods: Prime Minister Jacinda Ardern arrives to address civil defence workers

A slip fell onto this Tesla car in Lower Hutt.

But, rain has not just fallen in August. The entire winter will go down as Nelson’s wettest on record, despite there still being a week to go until the season officially ends.

Between the start of June and now, 738.8mm of rain has fallen in Nelson. The previous winter record was 569.7mm, recorded in 1970.

Noll said Niwa was now investigating the strength of the atmospheric river – a huge plume of moisture from the tropics – that caused the worst of the Nelson rain.

“What we’re kind of expecting to find is that it’ll end up being New Zealand’s strongest atmospheric river on record for the month of August, but that’s kind of pending the results,” he said.

Noll said the atmospheric river seen in Nelson last week was generally more likely to occur in summer or autumn.

“To have it during August is not unprecedented, but the intensity of the event that we saw last week, that may be unprecedented for the month of August,” Noll said.

Nelson was not the only place hit.

On Sunday, several roads in Wellington were closed, and eight households were evacuated following 160 slips.

Parts of the Far North also flooded last week, when more than a month’s worth of rain fell in just 24 hours.

On Friday, 350 homes and businesses in the Far North region were without power. The region itself was cut off when two state highways closed due to flooding and slips.

The West Coast was also hit with heavy rain last week, but the region “dodged a bullet” damage-wise as it avoided widespread flooding.

Another deluge is expected in Westland later this week.

The rest of the South Island experienced the worst of the wet weather last month.

Christchurch was hit by three storms throughout July – and the month has now gone down as the city’s wettest July on record.

During the last of the three storms, streets were flooded and there were slips across Banks Peninsula.

Christchurch has invested millions of dollars in flood defence work over the past decade. While it was widely considered to have protected the city from the worst impacts last month, it was nearly overwhelmed.

The city has pledged to spend another $220m on flood defences in the next 10 years.

Also in July, residents were evacuated in Dunedin’s student quarter amid fears of the rising water levels in the Water of Leith stream.

Residents were allowed to return the next day, but not before two daredevils took to surfing the swollen waterway.