Effects of the El Niño–Southern Oscillation in Australia are present across most of Australia, particularly the north and the east, and are one of the main climate drivers of the country. Associated with seasonal abnormality in many areas in the world, Australia is one of the continents most affected and experiences extensive droughts alongside considerable wet periods that cause major floods. There exist three phases — El Niño, La Niña, and Neutral, which help to account for the different states of ENSO.The beasts to our east: What are El Ninos and La Ninas? By Peter Hannam from the Sydney Morning Herald, December 29, 2020.
Between 1900 and 2023, there have been 28 El Niño and 19 La Niña events in Australia including the 2023 El Niño event, which was declared in September in 2023.La Niña In Australia Bureau of Meteorology. www.bom.gov.auEl Niño in Australia Bureau of Meteorology. www.bom.gov.au The events usually last for 9 to 12 months, but some can persist for two years, though the ENSO cycle generally operates over a time period from one to eight years.What is La Nina and what does it mean for your summer? By Peter Hannam and Laura Chung. The Sydney Morning Herald. November 25, 2021.
In La Niña years, the eastern seaboard of Australia records above-average rainfall, usually creating damaging floods due to stronger easterly trade winds from the Pacific towards Australia, thus increasing moisture in Australia. El Niño is associated with a weakening, or even a setback, of the prevailing trade winds, and this, results in reduced atmospheric moisture in Australia. Many of the worst bushfires in Australia accompany ENSO events, and can be exacerbated by a positive Indian Ocean Dipole, where they tend to cause a warm, dry and windy climate.
Climate Modelling The Bureau of Meteorology is Australia’s governing body for monitoring climate drivers and model data. All climate models developed at leading international climate agencies are utilised by the Bureau for climate driver monitoring and data sourcing. All models use an ensemble method, where several forecasts are run at the same time using slightly different initial conditions. While all models use ensemble techniques, the number of ensembles differs for each model.
The Climate Model Summary is updated on the 12th of each month, or the next working day, when model data becomes available. Data for the Bureau's model, ACCESS–S, is updated fortnightly along with several other models that also provide more frequent updates during the month.
Impacts El Niño
El Niño episodes are defined as continuous warming of the central and eastern tropical Pacific Ocean, thus resulting in a decrease in the strength of the Pacific trade winds, and a reduction in rainfall over eastern and northern Australia, particularly in winter and spring. An El Niño event typically begins in autumn and fully forms during winter and spring, but would then would start to dissipate by summer, with the event usually concluding in the autumn of the next year. Snow depth during El Niño years is generally lower in Australia's alpine regions.
El Niño years generally experience warmer-than-average temperatures with hotter daily temperature extremes across the south, especially in spring and summer. Even though temperature maxima is occasionally warmer than average, reduced cloud cover frequently produces a cooler temperature minimum during winter-spring and a longer frost season.
El Niño's effect on Australian rainfall decreases after November, particularly in the southeast, and therefore a pronounced difference between the rainfall patterns of early and late summer would exist. Nonetheless, Cape York and northwest Tasmania would have moderately dry conditions. Some areas on the Queensland/New South Wales border exhibit a small inclination for wetter conditions. There is also a reasonably stronger propensity for wetter than average conditions in the southeast of Western Australia.Climate Driver Update www.bom.gov.au. Retrieved 27 November 2021.
La Niña La Niña episodes are defined as uninterrupted cooling of the central and eastern tropical Pacific Ocean, thus resulting in an increase in the strength of the Pacific trade winds, and the opposite effects in Australia when compared to El Niño. In the La Niña case, the convective cell over the western Pacific strengthens inordinately, resulting in colder than normal winters in North America and a more intense cyclone season in South-East Asia and Eastern Australia with above-average winter–spring rainfall. There is a strong correlation between the strength of La Niña and rainfall: the greater the sea surface temperature and Southern Oscillation difference from normal, the larger the rainfall change.
La Niña is characterised by increased rainfall and cloud cover, especially across the east and north that continue into the warm months (unlike El Niño events); the average December–March precipitation is 20% higher than the long-term average, particularly in the east coast. Snow depth and snow cover is increased in the southeast during winter. There are also cooler daytime temperatures south of the tropics (especially during the second half of the year) and fewer extreme highs, and warmer overnight temperatures in the tropics. There is less risk of frost,Fewer frosts. Bureau of Meteorology. but increased risk of widespread flooding, tropical cyclones, and the monsoon season starts earlier. La Niña Modoki leads to a rainfall increase over northwestern Australia and northern Murray–Darling basin, rather than over the east as in a conventional La Niña.
SOI and IOD The Southern Oscillation is the atmospheric component of El Niño. This component is an oscillation in surface air pressure between the tropical eastern and the western Pacific Ocean waters. The strength of the Southern Oscillation is measured by the Southern Oscillation Index (SOI). The SOI is computed from fluctuations in the surface air pressure difference between Tahiti (in the Pacific) and Darwin, Australia (on the Indian Ocean): El Niño episodes with negative SOI means there is lower pressure over Tahiti and higher pressure in Darwin; La Niña episodes with positive SOI means there is higher pressure in Tahiti and lower in Darwin.
In several recent studies, it is shown that the Indian Ocean Dipole (IOD) has a much more significant effect on the rainfall patterns in south-east Australia than the El Niño-Southern Oscillation (ENSO) in the Pacific Ocean. It is further demonstrated that IOD-ENSO interaction is a key for the generation of Super El Ninos. When an El Niño occurs with a positive IOD, the two events can strengthen their dry impact. Similarly, when La Niña coexists with a negative IOD, the chance of above-average winter–spring rainfall generally increases.Indian Ocean influences on Australian climate - When the Indian and Pacific oceans work together The Bureau of Meteorology. Retrieved 2 December 2021.
History Paleoclimate record During the Last Glacial Maximum, around 45,000 years ago, moisture variability in the Australian core shows dry periods related to frequent warm events (El Niño), correlated to DO events. Although no strong correlation was found with the Atlantic Ocean, it is suggested that the insolation influence probably affected both oceans, although the Pacific Ocean seems to have the most influence on teleconnection in annual, millennial and semi-precessional timescales.
1880s–1920s
1885 to 1898 were mostly La Niña years, being generally wet, though less so than in the period since 1968. The only noticeably dry years in this era were 1888 and 1897. Although some coral core data suggest that 1887 and 1890 were the wettest years across the continent since settlement. In New South Wales and Queensland, however, the years 1886–1887 and 1889–1894 were indeed exceptionally wet La Niña years, and February 1893 saw the disastrous 1893 Brisbane flood.Foley, J.C.; Droughts in Australia: review of records from earliest years of settlement to 1955; published 1957 by Australian Bureau of Meteorology
1903–04 were La Niña years, which followed the Federation drought, though two major El Niño events in 1902 and 1905 produced the two driest years across the whole continent, whilst 1919 was similarly dry in the eastern states apart from the Gippsland. 1906–07 were moderate La Niña years with above-average rainfalls. 1909 to early 1911 were strong La Niña years.
The 1911–1915 period were El Niño years, where Australia suffered a major drought. Drying of the climate took place from 1899 to 1921, though with some interruptions from wet El Niño years, especially between 1915 and 1916–18 and 1924–25, and 1928.
1920s–1960s The period from 1922 to 1937 was particularly dry with most years having a positive El Niño phase, with only 1930 having Australia-wide rainfall above the long-term mean. The Australia-wide average rainfall for those seventeen years was 15 to 20 percent below that for other periods since 1885. This dry period is attributed in some sources to a weakening of the Southern OscillationAllan, R.J.; Lindesay, J. and Parker, D.E.; El Niño, Southern Oscillation and Climate Variability; p. 70. and in others to reduced sea surface temperatures. During World War II, eastern Australia suffered El Niño conditions, which lasted from 1937 to 1947 with little relief, despite a few weak and relatively dry La Niña years in between (1938–39 and 1942–43).
1949–51 were La Niña years, which had significant rain events in central New South Wales and most of Queensland: Dubbo's 1950 rainfall of can be estimated to have a return period of between 350 and 400 years. Lake Eyre filled for the first time in thirty years. 1954–57 were also intense La Niña years. In contrast, 1951–52, 1961 and 1965 were very dry, with complete monsoon failure in 1951–52 and extreme drought in the interior during 1961 and 1965. 1964–69 were moderate La Niña years. Conditions had been dry over the centre of the continent since 1957 but spread elsewhere during the summer of 1964–65. The El Niño conditions from 1965–70 contributed to the 1967 Tasmanian fires.
1970s–1990s
The wettest periods in the 20th century were from 1973 to 1976, peaking in 1974, all La Niña years. The drought in 1979–83 is regarded as the worst of the twentieth century for short-term rainfall deficiencies of up to one year and their over-all impact. An El Niño event brought severe dust storms in north-western Victoria and severe bushfires in south-east Australia in February 1983. This El Niño-related drought ended in March, when a monsoon depression became an extratropical low and swept across Australia's interior and on to the south-east in mid-to late March. 1987–88 were weak El Niño years. 1988–89 had a strong La Niña event affecting the southeast half of the country.
Most of the 1990's were characterised by El Niño events; Beginning in the second half of 1991, a very severe drought occurred throughout Queensland which intensified in 1994 and 1995, to become the worst on record.Rankin, Robert. (1992) Secrets of the Scenic Rim. Rankin Publishers (page 151)Collie, Gordon. Dry tears of despair. The Courier-Mail. p. 29. 22 October 1994. From July to August 1995 the drought was further influenced by a strong El Niño weather pattern associated with high temperatures.Collie, Gordon. Water crisis threatens towns. The Courier Mail p. 3. 3 June 1995
Dry conditions began to emerge in south-eastern Australia in late 1996 and accentuated during the strong 1997 El Niño event. Despite the fact that the 1990s mostly consisted of El Niño years, a La Niña event formed from May 1998 where, in April 1999, it brought the notorious 1999 Sydney hailstorm.Australian rainfall during El Niño and La Niña events www.bom.gov.au Bureau of Meteorology
2000s