The nationwide average temperature in New Zealand was 13.76C in 2022, making it the warmest year for Aotearoa on record.
NIWA has released its 2022 Annual Climate Summary, showing the country's average temperature last year was 1.15C warmer than the 1981-2010 annual average. It was also 0.2C warmer than 2021, which previously held the record for warmest year.
The four warmest years on record have now all occurred since 2016, which NIWA said is a trend consistent with climate change.
No months in 2022 were below the average temperature, while 10 of the 12 months were either above average (meaning 0.51C to 1.2C warmer than usual) or well above average (more than 1.2C warmer).
"The most unusually warm month was November at +1.6 ̆C above average and the most unusually cool month was October, which despite featuring a significant cold spell with near sea-level snow at the beginning of the month, was still +0.2 ̆C compared to the long-term October average."
Leigh recorded the highest annual average temperature across the mainland for 2022 at 18C, followed by Kaitaia at 17.2C and Whangaparāoa at 17.1C.
The highest air temperature was 34.7C at Lake Karapiro on January 3, followed by 34.2C at Alexandra and 34.0C at Clyde, also recorded on January 3.
The lowest air temperature of the year was -11.6C at Mt Cook Airport on July 17, followed by -11.2C at Middlemarch on June 23, and -11.0C at Tara Hills (near Ōmarama) on June 22.
Taranaki had the highest annual sunshine total of the year with 2659 hours recorded in New Plymouth.
Despite the record warmth, NIWA said 2022 was also New Zealand's eighth most unusually wet year on record and the most unusually wet year since 2018.
The wettest locations in 2022 were Cropp River (West Coast, 975m above sea level) with 11034mm, Tuke River (West Coast, 990m above sea level) with 10510mm, and Hokitika (West Coast, 427m above sea level) with 8475 mm.
The lowest rainfall recording locations for 2022 were Roxburgh and Middlemarch with 368 mm, followed by Alexandra with 377 mm.
"The top three daily rainfall totals from regularly reporting gauges in 2022 were 692 mm at North Egmont on 18 August, 498 mm at Castle Mount on 18 February, and 387 mm at Mueller Hut on 2 February," NIWA said.
"The top three daily rainfall totals from regularly reporting gauges in 2022 excluding high elevation stations were: 282 mm at Arthurs Pass on 2 November, 245 mm at Upper Tākaka on 17 August, and 229 mm at New Plymouth (Hurford Rd) on 5 February."
Of the main centres, NIWA said Tauranga was the wettest, Dunedin was the driest and coolest, Auckland was the warmest, Hamilton was the sunniest, and Wellington was the least sunny.
The highest confirmed wind gust was 233km/h at Cape Turnagain on June 14.
Last year was the third consecutive year of La Niña, which is what is known as a "triple dip". NIWA said the last time that happened was between 1998 and 2000.
La Niña is among the main contributors to the unusual warmth and wetness, NIWA reported.
"The primary driver was La Niña, marked by cooler than average ocean temperatures in the central and eastern equatorial Pacific. La Niña influences atmospheric circulation patterns in the Pacific Ocean and has flow-on effects to climate across the globe."
In New Zealand, NIWA said La Niña tends to be associated with higher-than-normal air pressure near and to the east of the country with lower pressures to the north.
"This pressure setup causes more sub-tropical, northeasterly winds than normal, driving up air and sea temperatures."
Warmer than average coastal sea surfaces temperatures (SST) can also drive up humidity, causing above-average air temperatures.
Coastal SSTs were either above or well above average every month in 2022, with December, November and January ranking as the top three most unusually warm months.
"This culminated in a marine heatwave (MHW) event, or unusually warm ocean temperatures over thousands of kilometres, that lasted much of the year. MHW conditions were most persistent in Northland, Auckland, Waikato, Bay of Plenty, Taranaki, Tasman, West Coast, and Southland."
Extra moisture in the air caused by a weather feature in the Indian Ocean was also transported to New Zealand.
"Climate change continues to influence New Zealand’s long-term temperature trend, which is increasing at a rate of approximately 1.17 ̆C ( 0.2 ̆C) per century according to NIWA’s seven-station series."