Issued 30 June 2022

Rainfall

The total area-averaged rainfall for northern Australia over the 2021–22 wet season (October to April) was 476.3 mm, which is almost exactly the 1961–1990 average of 476.4 mm. Below average rainfall (in the driest 30% of all wet seasons since 1900–01) was recorded in a small area of the western Pilbara coast of Western Australia, an area of the Top End away from the north coast extending to the northern Barkly District, in parts of the Gulf Country and the northern interior, and for small parts of the central Queensland coast (Figure 1). Above average rainfall (in the wettest 30% of all wet seasons) was recorded in the south of the Northern Territory across to Queensland's Central West and parts of Wide Bay and Burnett, over areas of northern Western Australia, and in northern Cape York Peninsula. Southern parts of the Northern Territory, an area of the west Kimberley coast, and pockets of western Queensland recorded rainfall in the top 10% of all wet seasons.

As is typical of La Niña periods, much of northern Australia saw an earlier than average northern rainfall onset date, when rainfall accumulated since 1 September reached 50 mm, particularly inland where many areas saw an onset date at least 4 weeks earlier than the 1981–2010 median (Figure 2). Western parts of Western Australia experienced a later northern rainfall onset date, where onset dates were at least 3 weeks later than the 1981–2010 median.

For most areas, there was a wetter than average start to the wet season period, including November 2021 being the fifth-wettest November on record (all years since 1900), and the wettest since 2000. Southern areas recorded monthly rainfall totals in the top 10% of all years since 1900, with some sites observing their highest November rainfall on record.

The first active monsoon period occurred late in December 2021, with an official monsoon onset date at Darwin of 26 December 2021, which was close to the average date, over all years since 1957, of 29 December. January 2022 rainfall was wetter than average, with parts of western Queensland, southern Northern Territory, and the Kimberley and eastern interiors of Western Australia experiencing rainfall in the top 10% of all years since 1900.

The wetter than average start was followed by a dry February and March 2022, especially over northern parts of the Northern Territory and central inland parts of Queensland, where rainfall totals were in the bottom 10% of all years since 1900.

April 2022 saw a wet end to the wet season period, with large parts of central and western Queensland, and areas of the north and north-east coasts of the state recording monthly rainfall totals in the top 10% of all years since 1900. Some sites observed their highest April rainfall on record.

Temperature

The mean maximum temperature for northern Australia's wet season was 1.32 °C above the 1961–1990 average (sixth-highest on record since 1910–11), while the mean minimum temperature was 0.84 °C above the average (eighth-highest on record).

Mean maximum temperatures were above average for most of northern Australia (Figure 3), especially towards the north where large areas had temperatures in the top 10% of all years since 1910. Parts of the north-east tropical coast of Queensland experienced their highest mean maximum temperatures on record for the wet season period. Mean maximum temperatures over southern inland parts of northern Australia, and pockets of the Pilbara coast were close to average.

As a region, November 2021 was the only month that recorded below average maximum temperatures across northern Australia, with inland areas recording temperatures in the lowest 10% of all years since 1910. Area-averaged maximum temperatures for October and December 2021 were among their 10 highest on record. The end of the season was exceptionally warm, with March and April 2022 being their highest and sixth-highest on record respectively, with the area-averaged anomaly (relative to 1961–1990) for both months exceeding 2 °C.

Mean minimum temperatures were also warmer than average for most of northern Australia (Figure 4), especially across Queensland and the northern half of the Northern Territory. Parts of the Top End, Cape York Peninsula, and the northern Queensland coast reported their highest mean minimum temperatures on record for the wet season period. Areas around the southern border of the Northern Territory and Western Australia observed below average mean minimum temperatures, while remaining areas reported close to average mean minima.

As a region, northern Australia in November 2021 and February 2022 recorded below average minimum temperatures, with all other months among their respective 10 warmest on record since 1910.

Water availability

Soil moisture and streamflow

Very much above average soil moisture (in the highest 10% of all years since 1911) and above average rainfall in north-west Queensland increased runoff and inflow only in the Julius storage during October 2021 (Figure 5). Above average streamflow (relative to all years since 1980) in north-east Queensland, did not affect water storages in those parts of the north.

Soil moisture increased to above average and very much above average in November 2021 (Figure 6), particularly in the central and southern parts of northern Australia. The same situation prevailed for streamflow except for the drier parts of the north and the north-east. However, this did not increase the water level in the majority of storages in the north, except for Julius dam.

December 2021 saw a drier soil moisture conditions in most areas of northern Australia (Figure 7), except for the eastern Queensland catchments, with very much above average streamflow and subsequent rises in some storages, including Burdekin FSalls, Lake Awoonga and Lake Ross.

While the eastern parts of northern Australia were drying out in January 2022 (Figure 8), central north and north-western areas had high to very high soil moisture and streamflow conditions. Apart from storages in dry areas of Queensland, water in most storages started to rise through the end of the month.

As a result of the January monsoon rainfall in the northern parts of northern Australia, the Argyle and Darwin River storages gradually filled in February 2022 (Figure 9), along with the Julius and Burdekin Falls storages in Queensland. Other parts of the eastern and central regions experienced dry conditions during February.

Except for the Kimberley region, which had average to above average soil moisture conditions, March 2022 was the driest month of the period for other parts of the northern Australia (Figure 10). Water storages gradually started to decline, although flows in some eastern streams were showing above their historical average.

In April 2022, wet conditions dominated the north-east and part of western Queensland, increasing the soil moisture in those areas, and a number of stream gauges recorded above average to very much above average flows (Figure 11). Dry conditions prevailed in the rest of northern Australia. Water levels in the Ross River and Paluma storages of coastal Queensland started to rise towards the end of the month.

Water storages

• Three storages (Burdekin Falls and Julius in Queensland and Darwin River in the Northern Territory) surpassed their capacity at times during the northern wet season (Figure 12)
• The largest increase in the water storages occurred in Burdekin Falls and Julius (Queensland), followed by Darwin River (Northern Territory), Tinaroo Falls (Queensland) and Lake Argyle (Western Australia)
• There was no considerable rise in rest of the water storages during the northern wet season

Climate influences

La Niña conditions were in place for much of the wet season for northern Australia. By August 2021, some signs of a resurgent La Niña event were emerging, with a La Niña WATCH issued by the Bureau of Meteorology in September moving to ALERT in October. La Niña onset was announced in November 2021. La Niña conditions persisted through summer 2021–22 and into autumn, with La Niña still active at the end of April. The weekly NINO3 SST index in the eastern tropical Pacific was at its coolest during January 2022 (−1.2 °C) and the weekly NINO3.4 SST index in the central tropical Pacific was at its coolest at the beginning of March 2022 (−0.86 °C).

La Niña typically brings above average rainfall to much of northern Australia during the wet season. The 2021–22 La Niña was conducive to the early start to the wet season and above average rainfall until January 2022. However, somewhat atypically for a La Niña, many areas of northern Australia were drier than average from February to April 2022.

The Indian Ocean Dipole (IOD) was in a negative phase at the start of the wet season, resulting in warmer than average sea surface temperatures in the eastern Indian Ocean. The negative IOD, and a warmer eastern Indian Ocean generally, was likely conducive to the above average rainfall observed in parts of northern Australia during October and November 2021. The IOD returned to a neutral phase by December 2021, in line with the typical life cycle of an IOD event. Above average sea surface temperatures across the eastern Indian Ocean may have contributed to cloud bands that brought rainfall to Western Australia, as well as inland parts of northern Australia.

The Madden–Julian Oscillation (MJO), which is the major climate influence for tropical Australia on weekly to monthly timescales, likely influenced tropical Australia at a few key points during the season. The MJO was in the Australian region during much of October and November 2021, potentially contributing to the wetter conditions across northern Australia during these months. However, MJO activity was almost completely absent from the Australian and Western Pacific regions between February and April 2022, with MJO activity in or near the western Indian Ocean. When the MJO activity is closer to Africa than Australia, there is often reduced cloudiness over northern Australia, with reduced convection and rainfall.

The lack of local MJO activity in the second half of the wet season likely contributed to an overall lack of strong monsoon activity over northern Australia. There were only 4 main active events of the Australian monsoon: around early November 2021, late in December 2021, and during the second half of January 2022. There were then no further monsoon bursts until late in April 2022.

The Southern Annular Mode (SAM) was mostly in a positive phase from October to December 2021, with the monthly SAM index value for December the second-highest on record (since 1979) behind 2011. At this time, the polar vortex over Antarctica was also particularly strong, likely contributing to the strongly positive SAM. From January to April 2022, the weekly SAM index was closer to neutral values, with brief periods of positive and negative values. The SAM averaged over the northern wet season was the third-highest since 1979–1980. In combination with La Niña, positive phase SAM is associated with above average rainfall over southern parts of the northern Australia during the wet season.

In addition to the influence of natural climate drivers, Australia's climate is increasingly influenced by global warming. Australia's climate has warmed on average by 1.47 ± 0.24 °C over the 1910–2020 period, with most of the warming occurring since 1950. Rainfall across northern Australia has increased during the northern wet season since the 1970s, with more high intensity and short duration rain events.

Significant events

Tropical cyclones

• For the Australian tropical cyclone region, as defined for the Tropical Cyclone Outlook, there were 8 tropical cyclones (Paddy, Ruby, Seth, Tiffany, Dovi, Anika, Vernon and Charlotte) with a ninth (Karim) forming in early May.
• The long-term average (since 1969–70) number of tropical cyclones in the Australian region is 11, while in recent decades (since 2000–01) the average is 9.
• Only two tropical cyclones (Tiffany and Anika) made landfall on the Australian mainland with at least Category 1 strength, which is fewer than the long term average of four.
• Tropical systems can have significant impacts even if they make landfall at below Category 1 strength, for example the remnants of Seth caused significant flooding in the Queensland Wide Bay and Burnett districts as it came ashore in early January 2022.
• Two tropical cyclones reached severe strength (at least Category 3) in the Australian region, compared to the long-term average of five. Vernon reached Category 4 in the Indian Ocean to the west of the Cocos and Keeling Islands during February 2022; and Charlotte reached Category 4 strength during March, remaining well off Western Australia's north-west coast.
• There were around 20 observed tropical lows in the Australia region during the October 2021 to April 2022 period.

Rainfall

Tropical Cyclone Seth

• Tropical Low 08U formed in the Arafura Sea on 24 December 2021. It tracked over the Top End, into the Gulf of Carpentaria and crossed the Cape York Peninsula on 29 December. Tropical Low 08U intensified into Tropical Cyclone Seth in the Coral Sea on 31 December, peaking at Category 2 strength.
• Seth then weakened and recurved back towards the southern Queensland coast as a sub-tropical system, where it crossed the Wide Bay and Burnett coast near Hervey Bay on 7 January 2021, bringing very heavy rainfall to the Capricornia, and Wide Bay and Burnett districts. Daily totals exceeding 600 mm were recorded at a few sites.

Tropical Cyclone Tiffany

• Tropical Cyclone Tiffany developed on 9 January 2022 from a tropical low that had recurved from the Gulf of Carpentaria into the Coral Sea.
• On 10 January, the system made landfall over the northern Queensland coast and rapidly weakened, producing daily rainfall totals between 50 mm and 150 mm over the Cooktown and Peninsula coasts.
• Tiffany re-intensified over the Gulf of Carpentaria into a Category 1 tropical cyclone and crossed the eastern Top End coast early on 12 January, and weakened, but produced moderate to locally heavy falls across most of the Top End from 12 January to 14 January (3-day totals greater than 150 mm for the most affected areas), and to the northern Kimberley coast and the northern interior of Western Australia from the 14 January to 16 January (3-day totals greater than 300 mm for parts of the Kimberley).
• The remnants of ex-Tropical Cyclone Tiffany then formed a complex low pressure system in central Australia on 16 January, bringing widespread moderate falls of 50 mm to 100 mm to southern and eastern parts of the Northern Territory from 17 to 20 January.

Heavy rain over north-western Australia

• An active phase of the monsoon during the last week of January 2022 resulted in the development of an extensive low pressure trough over the northern tropics. This trough, along with multiple embedded tropical lows, produced heavy rainfall over large parts of northern Australia that continued into early February.
• In particular, Tropical Low 14U brought significant rainfall to north-western Australia at the end of January and the beginning of February 2022. The Kimberley region was heavily affected. Country Downs recorded 652.2 mm on 1 February, the second-highest daily rainfall on record for Western Australia.

Tropical Cyclone Anika

• Tropical Cyclone Anika developed from a tropical low in the Timor Sea on 25 February 2022.
• Anika intensified to a Category 2 tropical cyclone before crossing the north Kimberley coast on the evening of 26 February and produced isolated heavy falls of 250 mm to 330 mm over the area.
• Anika weakened and tracked along the Kimberley Coast, producing daily totals up to 100 mm along the coast for the next several days.
• In early March, Anika had re-intensified to a tropical cyclone and crossed the far west Kimberley coast again on 2 March as a Category 1 tropical cyclone. It tracked south-eastwards through the eastern Pilbara, producing daily totals greater than 150 mm to 200 mm around the coast and totals of around 50 mm to 100 mm inland.

Heavy rainfall around Cape Arnhem

• Tropical Low 33U formed near the Top End on 16 April 2022 and brought heavy rainfall to Cape Arnhem. Gove recorded a two-day rainfall total of 350.6 mm with 221.4 mm being recorded on 17 April, the highest daily total since April 1999.

Heavy rainfall over Queensland

• A low pressure trough fed with tropical moisture brought widespread moderate to heavy rainfall to the Queensland coast on 22 and 23 April 2022, with the rainfall impacting inland areas from 24 to 26 April. A number of sites recorded their highest April daily rainfall on record.

Temperature

Heatwave over the Kimberley and Northern Territory

• A severe- to extreme-intensity heatwave affected the Kimberley district in Western Australia and northern and central parts of the Northern Territory from 19 October 2022. Multiple sites across the region recorded their highest October daily maximum or daily minimum temperature on record during this heatwave, including Wyndham Aero, which recorded 45.1 °C on 21 October.

Heatwave over the Pilbara

• The Pilbara experienced severe-intensity heatwave conditions a few times during December, with a number of sites reporting their highest December mean maximum or mean minimum temperature on record. This included Marble Bar, which recorded its highest mean maximum temperature and mean minimum temperature for December in 120 years of temperature observations (combining the current and old sites) at 44.7 °C and 28.7 °C respectively.

Extreme heat over northern and central Western Australia

• A hot air mass resulted in temperatures exceeding 40 °C over northern and central Western Australia between 12 and 14 January 2022, and exceeding 50 °C near the Pilbara coast. This included Onslow Airport, which recorded a maximum temperature of 50.7 °C on 13 January, the highest temperature recorded in Western Australia, and equal with the all-time highest temperature in Australia, set 62 years ago at Oodnadatta in South Australia on 2 January 1960.
• Marble Bar recorded a minimum temperature of 34.6 °C on 13 January, which was the highest minimum temperature for 106 years at Marble Bar, and the third-highest on record, behind 35.1 °C on 24 January 1916 and 35.0 °C on 28 December 1902.

Extreme heat across northern Australia

• From late February 2022 and into March, the northern and central coasts of Queensland experienced severe- to extreme-intensity heatwave conditions. The north of the Northern Territory also experienced heatwave conditions, with severe intensity in the north-east , resulting in several stations having their highest March daily maximum or daily minimum temperatures on record.
• Roebourne Aero recorded a maximum temperature of 47.1 °C on 16 March, which was its second-highest temperature in March, and an Australian late season record. Telfer Aero recorded a minimum temperature of 33.3 °C on 16 March, which was its highest minimum temperature in March on record, and the state and national equal fourth-highest minimum temperature for March on record.