The 'mild' winter that wasn't

Darfield in Canterbury was under 36cm of snow after June's storm. Picture / Christchurch Star

Niwa said it would probably be a mild winter, but with the chilly season officially on its way out next week experience suggests it wasn't.

The country has shivered through record snows in Canterbury, waded through floods in Coromandel, Otago and Wairarapa, been battered by gale force winds in Auckland, Taranaki and Waikato and dodged land slips in Wellington, Hawke's Bay and nearly everywhere else.

The wild weather kicked off early with heavy rain drenching parts of Otago in late April. Rivers broke their banks, roads and bridges were washed out, and motorists were stranded in their cars overnight.

In early May, more rain caused land slips which closed the Napier-Gisborne and Napier-Taupo roads.

The outlook seemed to be clearing on June 6, when the National Institute of Water and Atmospheric Research (Niwa) said it was likely to be a mild winter.

Instead, it would be the coldest June since 1972, with an average temperature of 7.3C. In Canterbury and North Otago the mercury dropped to -10C on nine days.

On June 12, Cantabrians woke up to the deepest snowfall they'd had since 1945, cutting power to more than 10,000 homes -- some of them for up to 18 days. And on June 22, another heavy dumping of snow across the central North Island closed all but one significant route between Auckland and Wellington.

July provided some respite from the plummeting temperatures -- it was 0.8C warmer than June -- but freezing cold snows were replaced with torrential downpours in many areas.

Rainfall was twice normal levels in Wairarapa, and 1-1/2 times normal in Wellington, Wanganui and King Country, causing widespread disruptions.

Slips blocked a crucial route between Hutt Valley and Wellington on July 5, and four houses were evacuated when the Ruamahanga River in South Wairarapa threatened to burst its banks.

On July 9 Mangamahu, a small town north of Wanganui, was cut off completely when a bridge over the Mangawhero River collapsed after heavy rains.

Not everybody bore the full force of the weather. Auckland, Hamilton and Dunedin all basked in the sunniest June on record. Auckland also had half its normal levels of rainfall in July, as did Coromandel and Central Otago. Northland and North Otago had a mere quarter of their normal levels.

Niwa scientists are quick to point out that they never said it was certain to be a mild winter.

"It may sound a bit like playing with words but what we said was it was likely to be mild," says Dr David Wratt of Niwa's National Climate Centre in Wellington.

Global weather

The Climate Centre uses computer models to simulate the global weather system. They run a number of different models several times, making small changes to each run, and average out the results to come up with the weather odds.

This winter they ran about nine models, says Dr Wratt, between 10 and 15 times each. Based on the results from these, they found there was a 50 per cent chance of a mild winter.

"But we also saw ... there was a 30 per cent chance of it getting very wet. So what actually happened was we got hit by the 30 per cent rather than the 50," he says.

"It makes our lives a bit miserable to tell you the truth, because we know the simple summaries we have to put out as press releases, some of the time will be wrong. And people will come back and criticise us. I won't say it's like being a politician, but there are certain jobs where it goes with the territory."

Dr Wratt says in fact it wasn't an exceptionally bad winter overall -- no matter how atrocious the weather might have seemed.

"There were certainly some places where the weather was very unusual, but not necessarily for the country as a whole."

But Insurance Council chief executive Chris Ryan says it was one of the most financially damaging winters New Zealand has seen in decades.

"The insurance payouts would conservatively be in the hundreds of millions of dollars ... It's been very long, very wet and very destructive."

He says one of the biggest concerns for the Insurance Council is the number of people who don't have insurance -- up to a third of some small communities.

According to Dr Jim Renwick, Dr Wratt's colleague at the National Climate Centre, people may have been caught off guard by this winter's severity because it bucked a warming trend.

"Over the last ten years or so we've had a predominance of warm winters. Maybe this winter has seemed that much colder because we've got un-used to having cold winters," he said.

In early August Niwa issued their forecast for a mild spring, saying it's likely to be warmer than average, and less windy. New Zealanders will have to wait and see.

- NZPA