La Niña events greatly influence Australia’s climate.
The 2010–11 and 2011–12 La Niña events were two of the most significant in Australia’s recorded meteorological history.
The following pages explore the ‘story’ and ‘background’ of these La Niña events. The ‘story’ section follows the evolution of these extraordinary events and their widespread impacts on the weather of Australia during 2010 through 2012. The ‘background’ section gives an overview of the physical processes driving La Niña and El Niño events, and outlines the ways in which these events typically alter weather in Australia.
Unless otherwise indicated, all temperature and rainfall anomalies (i.e. departures from average) in this publication are calculated with respect to the 1961–1990 average, as recommended by the United Nations World Meteorological Organization.
At a glance: the impact of these La Niña events in Australia
The successive La Niña events spanning 2010–12 were associated with record rainfall over much of Australia and some of the biggest floods in living memory. This followed years of severe drought in many parts of the country, and while it brought relief to many Australians, it also brought devastation to others.
Some facts about the 2010–11 and 2011–12 La Niña events
The 2010–11 La Niña event was one of the strongest on record, comparable in strength with the La Niña events of 1917–18, 1955–56 and 1975–76.
In October and December 2010, and February and March 2011, the Southern Oscillation Index values (a measure of a La Niña's strength) were the highest recorded for each month since records commenced in 1876.
2011 was Australia's coolest year in a decade (2001–2011).
2010 was Australia's third-wettest calendar year on record.
The Murray–Darling Basin experienced its wettest calendar year on record in 2010 and Western Australia experienced its wettest year on record in 2011.
2011 was Australia's second-wettest calendar year (with the wettest year since national rainfall records began in 1900 being 1974 – also a La Niña year).
Ocean temperatures to the north of Australia were highest on record in 2010.
April 2010 to March 2012 was Australia's wettest two-year period on record.
Widespread flooding occurred in many parts of Australia associated with the record rainfalls.