This year is shaping up to be one of New Zealand's worst ever for extreme weather events, following a spate of major fires, floods and storms.
Civil Defence officials declared a record number of weather-related state of emergencies - eight compared to one last year and four in 2015.
Insurers have meanwhile put losses from the year's events, all which hit in the first seven months, at $242 million - five times that of 2016's bill for extreme weather and also eclipsing others.
Meteorologists say it's not simply climate change at play, but a combination of ocean-driven effects that happened to make for a dramatic year.
2017 was tracking to finish somewhere between New Zealand's seventh and fourth hottest on record, with this month's heat likely pushing it toward the warmer end of the scale.
A helicopter joins the fight against wildfires that raged over the Port Hills, near Christchurch, in February. Photo / File
Niwa meteorologist Ben Noll said the year had been effectively book-ended by a weak La Nina climate system that quickly faded away in February and March, and a much stronger one that kicked into gear part-way through November.
In between, nearly every month of the year had been either near or above average.
"We had five months of near average temperatures and five months of above-average temperatures - and just one month, January, that had below-average temperatures.
"August was 1.3C above average, October was 1C above average and November was 1.1C above average - so you had some big boppers in there that were really pulling the weight at the top end."
But the year still started dry enough in some places to fuel large wildfires: notably blazes that scorched more than 2000ha of Christchurch's Port Hills in February, destroying 11 homes, and three weeks of fires in Hastings that led to a state of emergency declared.
Then came a series of major storms that battered the North Island, among them the remnants of Cyclone Debbie, which put much of Edgecumbe under water and forced the evacuation of 1600 residents, and Cyclone Cook soon after, which left thousands of households in the Bay of Plenty and Hawke's Bay without power.
Noll said 2017's high-rainfall events could be explained by a mix-and-match set-up of temperatures across the Pacific.
North Shore resident Lucy Knight at her home in Hillcrest which was flooded during Cyclone Debbie during April. Photo / File
While the sea surface temperatures near Peru had been warmed by a El Nino Costero - a variation of the normal climate system - those in the Central Pacific were cooler than average, while the Western Pacific remained warmer than average.
"So across the Pacific, we had warm, cool, warm - and that difference may have contributed to our wetness early in the season."
Now, a strong La Nina system had brought dominant high-pressure systems across much of the country, with abnormally high sea surface temperatures also cranking up the late-year heat.
"Our anomalies for November and December are going to be significant driven by the very warm sea temperatures that we have now surrounding New Zealand, and basically engulfing it.
"So it's not going to be colder than average when your sea surface temperatures are 2C-4C above average - that's just something that will never happen."
A state of emergency was declared in Hastings due to wildfires that scorched farmland near the Tukituki Valley. Photo / File
While it was difficult to factor in what background effects climate change might have had, these were expected to become more significant as the planet warmed.
But globally, a clear pattern was now emerging: 16 of the world's 17 hottest years have occurred since the turn of the century.
Niwa was expected to release its annual climate report early next month.
Our extreme year
State of Emergencies declared:
• Hawke's Bay fires: February 13-15 • Christchurch Port Hills fires: February 15-March 1. • Flood risk from Ex Tropical Cyclone Debbie in Whanganui and Rangitikei: April 4-6 • Edgecumbe flooding: April 6-11 • Flood risk in Bay of Plenty: April 11-14 • Severe weather risk in Thames-Coromandel: April 12-14 • Severe weather in Whakatane: April 14-21
Insurance costs:
• Nationwide severe weather, January 18-23, $8.6m • Dunedin flooding, February 13, $1.7m • Port Hills fires, February 13-17, $18.3m • Upper North Island flooding, March 7-12 $61.7m • Cyclone Debbie remnants, April 3-7 Apr, $91.46m • Cyclone Cook remnants, April 13-16, $17.2 • Nationwide snow/wind/rain, July 12-14, $12.5m • South Island flooding, July 20-22 - $31.1m
