Thread by @NiwaWeather

It's official, 2021 was Aotearoa New Zealand’s warmest year on record 🌡️

The trend is not our friend — it's our foe.

niwa.co.nz/climate/summar…

🧵 on the 21 things you should know about 2021, through the eyes of @niwa_nz's climate scientists

@niwa_nz The year 2021 finished with an average temperature of 13.56°C in New Zealand.

This was 0.95°C above average and surpassed 2016 to become the country's new warmest year on record.

New Zealand's average annual temperature has increased by about 1°C over the past 100 years 📈

@niwa_nz The recipe for New Zealand's warmest year on record in 2021? 🧑‍🍳 ♨️

You guessed it: climate change.

Other factors:

• La Niña

• Northerly winds

• Marine heatwave

• High pressure

@niwa_nz 2021 climate extremes in New Zealand 🎚️

🥵 Hottest: 39.4˚C, Ashburton

🥶 Coldest: -10.8˚C, Tara Hills

🌧️ Wettest: 14,090 mm, Cropp River

🏜️ Driest: 402 mm, Alexandra

🌬️ Max wind gust: 222 km/h, Cape Turnagain

@niwa_nz How does the 2021 annual temperature compare to the long term 1981-2010 average?

The year finished with an average temperature of 13.56°C. This was 0.95°C above average.

🟥 Red bars indicate years with above average temps

🟦 Blue bars indicate years with below average temps

@niwa_nz In 2022, NIWA will transition to using the 1991-2020 reference period for computing temperature anomalies.

The new baseline will help to better contextualise recent climate conditions.

Using this warmer reference period, 2021 would be considered to be 0.82°C above average.

For a long time series like NIWA's seven-station series, @WMO recommends also using the 1961-1990 reference period.

This helps to show how much the climate has changed.

When compared to this colder 30-year average, the year 2021 would be considered to be 1.09°C above average.

@WMO 💡 Changing the reference period helps put our climate into context but does not affect the observed temperature or the rankings.

No matter the baseline, seven of the past nine years have been among our warmest on record 🔥

@WMO 2021 was the warmest year on record for 12 locations 🌶️

An additional 50 locations experienced annual average temps in the top four warmest on record.

• 9 months had above average temps

• 3 months had near average temps

• 0 months had below average temps

@WMO During 2021 in New Zealand.....

⬆️ 55% of days had above average or well above average temperatures

↔️ 19% of days had near average temperatures

⬇️ 26% of days had below or well below average temperatures

@WMO Rainfall in New Zealand during 2021—

It was about the extremes.

🏜️ Extended dry spells due to high pressure were interspersed with extreme rainfall events 💧

More frequent northerly-quarter winds transported moisture from the tropics to New Zealand.

@WMO Early 2021 featured extended dry spells in the North Island.

According to NIWA's New Zealand Drought Index:

🌵 Meteorological drought in the Far North, Hawke's Bay & Gisborne

🌵 Very to extremely dry conditions across the North Island & eastern South Island

@WMO 🌊 Atmospheric rivers -like rivers in the sky- commonly flowed toward New Zealand during 2021.

Three flooding events resulted in State of Emergency declarations:

🌧️ Canterbury (29-31 May)

🌧️ West Coast, upper South Island & Wellington (15-18 July)

🌧️ Gisborne (3-5 November)

@WMO 🌊 Canterbury flooding, May 2021 — a 1:200 year flood for parts the region.

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.

🌊 West Coast flooding, July 2021 — flood flows (7640 cumecs) at the Buller River reached the highest flow rate ever recorded in a New Zealand river.

Preliminary findings show that extreme precipitation events in the Buller basin are 1.5 times more likely because of emissions.

New Zealand's 2021 climate was influenced by a variety of drivers, as is typically the case.

La Niña, marked by cooler than average (🔵) ocean temps in the equatorial Pacific, was active during Jan-Feb & Dec.

For 2021 as a whole, this was associated with more northerly winds.

🔥 A record-breaking marine heatwave event (MHW) emerged in the North Island's coastal waters during Nov & persisted through Dec 🌊

Daily SSTs reached as high as 4˚C to 5˚C above average around the western and northern North Island, elevating air temps and humidity 🥵

The Southern Annular Mode (SAM), an indicator of Southern Hemisphere climate variability, was positive 73% of the time during 2021 🔴

This was the 4th highest percentage on record.

The positive SAM phase is associated more high pressure and tranquil conditions in New Zealand.

Our warming climate is evident when looking at 2021 global temperatures 📈

Despite La Niña last year, 77% of the planet experienced above average temps (relative to 1981-2010).

New Zealand is not alone: 2021 was the 5th warmest year globally according to @CopernicusECMWF.

☀️ The sunniest region of 2021 was Taranaki with an annual total of 2592 sunshine hours (recorded at New Plymouth).

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 ☁️

📖 If you're interested in viewing NIWA's 2021 Annual Climate Summary as a story map, follow the link below!

(we think it's pretty cool 😎)

If you have any feedback, we would be most grateful 🙏 thanks for stopping by & hope you learned something!

🌞

arcg.is/0D5Gnn