Effects of the El Niño–Southern Oscillation in Australia
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.
Conversely, El Niño events will be associated with a weakening, or even a setback, of the prevailing trade winds, and this, results in reduced atmospheric moisture in the country.
[7] Many of the worst bushfires in Australia accompany ENSO events, and can be exacerbated by a positive Indian Ocean Dipole, where they would tend to cause a warm, dry and windy climate.
All models use an ensemble method, where several forecasts are run at the same time using slightly different initial conditions.
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.
Similarly, when La Niña coexists with a negative IOD, the chance of above-average winter–spring rainfall generally increases.
[27] During World War II, eastern Australia suffered El Niño conditions which lasted from 1937 through to 1947 with little relief, despite a few weak and relatively dry La Niña years in between (1938–39 and 1942–43).
1987–88 were weak El Niño years, with 1988–89 featuring 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.
[34][35][36][32][37] Dry conditions began to emerge in south-eastern Australia during 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.
[44] In early 2007, forecasters believed that the El Niño effect that had been driving the drought since 2006 had ended, though the Murray–Darling Basin experienced their seventh consecutive year of below-average rain.
[47] Although 2007 to early 2009 were moderate La Niña years, hot and dry conditions still prevailed in parts of south-eastern Australia, with occasional heavy rainfall failing to break the continuing drought.
[49] According to the Bureau of Meteorology's 2011 Australian Climate Statement, Australia had lower than average temperatures in 2011 as a consequence of a La Niña weather pattern.
The combination of heat and low rainfall brought a very early start to the 2015–16 Australian bushfire season, with over 125 fires burning in Victoria and Tasmania during October.
[57] During the 2014–2016 El Niño event, the 2015–16 Australian region cyclone season was the least active since reliable records started during 1950s.
[69] From late February to early March 2022, southeastern Queensland and northeastern New South Wales experienced significant rainfalls and flooding, which marked the phase of two years of wet La Niña summers in eastern Australia.
[73][74] In March 2023, La Niña was officially declared over in Australia, with sea surface temperatures returning to normal or neutral.
[75] In July 2023, the World Meteorological Organization declared that El Niño has developed in the tropical Pacific for the first time in 7 years.
[76] In September 2023, the Bureau of Meteorology formally declared an El Niño weather event, for the first time in 8 years, after hot and dry conditions prevailed over south-east Australia during spring.
