Annual Climate Summary 2021
A recap of the climatic facts and figures for Aotearoa New Zealand
Temperature
In order to calculate how the average temperature for 2021 compares to previous years, we can look at NIWA's 'seven-station' temperature series (which extends back to 1909). With an average annual temperature of 13.56°C, 2021 has become Aotearoa New Zealand's warmest year on record, surpassing the previous record set in 2016. This long running record shows New Zealand's average annual temperature has increased by about 1°C over the past 100 years.
New Zealand seven-station time series 1909-2021
By plotting the seven-station series as anomalies we can see how the annual temperature compares to a long term average.
Meteorological agencies around the world generally use a 30-year baseline to put our climate into context. The World Meteorological Organisation (WMO) describes "standard reference periods" to maintain consistency in the calculation of climate statistics across the world. This allows climate statistics from different countries to be compared and analysed.
For this year's Annual Climate Summary we have used the 1981-2010 reference period.
Red bars indicate years with above average temperatures
Blue bars indicate years with below average temperatures
With an average temperature of 13.45°C, the year 2016 measured 0.84°C above average and became New Zealand's warmest year on record at the time.
The year 2021 finished with an average temperature of 13.56°C. This was 0.95°C above average and surpassed 2016 to become New Zealand's new warmest year on record
During 2022, NIWA will transition to using the most recent 1991-2020 reference period for referring to temperature anomalies in climate summaries.
Using this warmer reference period, the 2021 annual average temperature would be considered to be 0.82°C above average.
For the purposes of historical comparison and climate change monitoring, WMO recommends using the 1961-1990 period for calculating and tracking global climate anomalies relative to a fixed and common reference period. When compared to this 30-year average, the year 2021 would be considered to be 1.09°C above average.
Changing the reference period helps to put our climate into context but does not affect the actual temperature observed or the temperature rankings.
No matter the reference period, seven of the past nine years have been amongst some of our warmest on record.
Monthly temperatures
For the year as a whole, it was the warmest year on record for 12 locations and a further 50 locations experienced annual average temperatures in the top four warmest on record. There was of course variability throughout the year regionally and temporally.
Based on the 7-station series...
3 months of the year experienced near average temperatures
9 months of the year experienced above average temperatures
No months experienced below average temperatures
Daily temperatures
Daily data based on NIWA’s Virtual Climate Station Network shows that for the country as a whole...
26% of days had below average (less than -0.5°C below average) or well below average (less than -1.2°C below average) temperatures
19% of days had near average (within 0.5°C of average) temperatures
55% of days had above average (greater than 0.5°C above average) or well above average (greater than 1.2°C above average) temperatures
The hottest spell of the year took hold over New Zealand from 25-28 January, with several locations observing record or near-record high daily maximum and daily minimum temperatures. 17 locations experienced a day with record or near record high maximum temperature (hot day) during 2021 and 10 locations experienced a near record high minimum temperature (warm night).
The highest temperature of 2021 was recorded on 26 January at Ashburton. The maximum temperature there reached 39.4°C, which is New Zealand’s 2nd-highest January temperature on record, and the country’s 10th-equal hottest temperature on record for all months.
On May 27th the temperature at Dunedin Airport dropped to -8.8°C overnight. This was the equal-lowest temperature on record there with records extending back to 1962. This was the only location to experience a record or near record low minimum temperature (cold night) in 2021.
No locations experienced a record or near record cold day in 2021.
Rainfall
Dry start to the year
The start of the year featured extended dry spells in the North Island.
Meteorological drought occurred in the Far North district during January (based on the NZ Drought Index pictured) and very dry to extremely dry conditions became widespread across large parts of the North Island as well as Marlborough and northern Canterbury during February.
Water restrictions were in place for a time in Northland, Auckland, Wairarapa and the Hastings District.
While 2021 featured extended dry spells owing to frequent high pressure there were also several extreme rainfall events.
29-31 May - Canterbury
A prolonged and heavy rainfall event struck Canterbury. A state of emergency was declared across the region, with severe flooding occurring in many areas east of the eastern foothills.
Damage caused by flooding was widespread, with numerous roads closed, bridges damaged and impassable, and farms suffering considerable impacts to infrastructure and stock. Hundreds of residents from several settlements were forced to evacuate, including the entire town of Springfield. There were several reports of people getting caught by the floodwaters and requiring rescue.
Research after the event carried out by the EWERAM project found that the extreme rainfall was 10-15% more intense as a result of human influence on the climate system.
15-18 July: West Coast - Marlborough
From 15 July to 18 July, a pulse of tropical air deriving from the Indian Ocean combined with an upper level trough and front to direct a humid and gusty northerly flow to the central and northern South Island.
The event led to flows at the Buller River reaching flow rates higher than ever recorded in a New Zealand river. Residents in parts of Westport were forced to evacuate as the river burst its banks, leaving waist-high water in many areas.
Floodwaters also cut off areas of Marlborough and nearly 1000 people had to evacuate. In the aftermath of the flood, at least 200 homes in Westport were deemed uninhabitable and at least 1000 stock were lost due to the floods. The flooding resulted in an estimated $132.4 million in privately insured damage according to the NZ Insurance Council .
30-31 August: Auckland
A stalled low pressure system, in conjunction with a strong ridge of high pressure near the South Island, contributed to an enhanced thermal gradient over the Auckland region led to near-record rainfall over northwestern Auckland.
Considerable flooding was reported in some areas including Kumeū, Helensville, Henderson Valley and Rānui, with an evacuation centre set up for the approximately 60 households forced to leave their home. Approximately 400 homes were without power, with slips and downed trees causing issues for the electricity infrastructure. At least 11 roads were closed due to flooding and slips.
Although this flooding event was localised, it was the second costliest weather event of the year in terms of insured damage.
3-5 November: Gisborne region
A slow-moving subtropical low caused persistent heavy rainfall that affected the eastern North Island and brought flooding and slips to parts of Gisborne, resulting in a State of Emergency being declared.
A search and rescue squad used boats to evacuate residents from flooded homes. The heavy rain caused Gisborne District Council to open the emergency sewer valve at Wainui Road into the Turanganui River to prevent sewage from overflowing back into homes and onto roads.
In less than one day Gisborne also received more rainfall than it did during all of summer 2020-2021 (67 mm).
Three flooding events during 2021 resulted in State of Emergency declarations: Canterbury flooding (29-31 May), West Coast, upper South Island and Wellington flooding (15-18 July) and Gisborne flooding (3-5 November). Atmospheric river events commonly flowed down toward New Zealand, driving precipitation extremes.
With the exception of February and March, every other month of the year had at least one location experience their wettest day on record.
Click on the circles to see details on the locations which experienced record high monthly extreme 1-day rainfall totals.
Climate drivers
The climate during 2021 was influenced by a variety of drivers, as is typically the case in New Zealand.
La Niña
During January and February, moderate La Niña conditions in the central Pacific (which began in October 2020) gradually eased. In New Zealand, impacts on weather patterns from this climate driver were generally not consistent with those typically expected, which likely owed in part to an non-traditional variety of La Niña.
Autumn 2021 was characterised by long dry spells and warmth, interspersed by bursts of heavy rainfall. This was because La Niña waned in March and the dominant climate driver became the Madden-Julian Oscillation (MJO), an eastward moving “pulse” of cloud and rain in the tropics.
Re-developing La Niña conditions during spring resulted in a transition from a westerly air flow, near average temperatures and widespread wet weather during September to more north-easterly winds during October-December, bringing frequent warm and humid weather and contributing to the country’s 5th-warmest October, warmest November and 4th-warmest December on record.
Warm coastal waters
A warm end to the year was helped along by increasing coastal sea surface temperatures (SSTs), particularly in November when marine heatwave (MHW) conditions emerged and persisted through December. During December, daily SSTs reached as high as 4˚C to 5˚C above average around the western and northern North Island, qualifying as one of the strongest MHW events in the last four decades in the North Island’s coastal waters.
Southern Annular Mode
The Southern Annular Mode , an indicator of Southern Hemisphere climate variability, was positive 73% of the time during 2021. The positive SAM phase is associated with higher than normal air pressure around New Zealand, which tends to bring more tranquil weather conditions to the country.
Northeasterly winds
Frequent high pressure over the North Island and east of New Zealand, caused more northerly quarter winds than normal and was a contributor to New Zealand’s warmest year on record.
Climate change
La Niña is often associated with cooler temperatures for the Earth as a whole as it causes upwelling of cooler water in the tropical Pacific.
Despite La Niña being present for much of 2021, 77% of the planet experienced above average temperatures (relative to 1981-2010 baseline). Our warming climate is evident in the seven-station series and also when looking at global temperature trends.
Sunshine
In 2020 the Bay of Plenty took out the sunshine crown with annual total of 2704 sunshine hours (recorded at Whakatāne). Frequent north-easterlies brought cloudier than usual weather to the Bay in 2021 and Whakatāne finished with just 2291 sunshine hours for the year.
The sunniest region of 2021 was Taranaki with an annual total of 2592 sunshine hours (recorded at New Plymouth). Interestingly, there was 8 more hours of sunshine recorded at New Plymouth in 2020 than 2021. New Plymouth takes the sunshine crown because the usual top 3 contenders of Bay of Plenty, Nelson and Marlborough had a cloudier than usual year.
The numbers
You can read the full 2021 Annual Climate Summary and find all the facts and figures here
