In 2010, Australia experienced its third-wettest year since national rainfall records began in 1900, with second place taken by 2011. Averaged across Australia, both years experienced rainfall well above the long-term average of 465 mm – 703 mm in 2010 and 708 mm in 2011.
Only 1974, dominated by one of the strongest La Niña events on record, was wetter with 760 mm. 2010 was also the wettest year on record for the Murray– Darling Basin and Queensland, while 2011 was the wettest year on record for Western Australia.
During the 2010–11 La Niña, most of Australia experienced significantly higher than average rainfall over the nine months from July 2010 to March 2011. Parts of Tasmania also received heavy rainfall while southwest Western Australia missed out, remarkably experiencing its driest year on record. A number of new Australian rainfall records were set: wettest September, December and March on record and second-wettest October and February. May to October 2010 was the wettest 'dry' season on record in northern Australia, and July to December 2010 was the wettest second half of the year on record for Australia as a whole.
Several seasonal records were also set: wettest spring on record for Australia, and all States except Victoria and Tasmania; wettest summer on record for Victoria; and second-wettest summer on record for Western Australia and Australia as a whole.
While the 2010–11 La Niña event was costly in an economic and social sense, it relieved one of the longest and most severe droughts across the Murray– Darling Basin in recorded history. Heavy rain provided a significant boost to water storages in Queensland, New South Wales and South Australia. Nationally, water held in major publicly owned storages rose by more than 20 per cent between May 2010 and May 2011.
During the 2011–12 La Niña, rainfall was above average for most of mainland Australia for the six months from October 2011 to March 2012, but not as much above average as for the 2010–11 event. Nevertheless, several rainfall records were set: second-wettest November and spring on record for Western Australia, and second-wettest March for New South Wales.
Combined, the two events yielded Australia's wettest 24-month period on record (April 2010 to March 2012), and wettest two-calendar year period (2010–2012). The record rainfall of 1411 mm in 2010–2011 beat the previous record of 1407 mm from 1973–1974.
The record-breaking rainfall during the 2010–11 La Niña led to widespread flooding in many regions between September 2010 and March 2011. As well as the severe flooding in southeast Queensland, large areas of northern and western Victoria, New South Wales, northwestern Western Australia and eastern Tasmania were subject to significant flooding. There were also some highly unseasonable rain events in the tropics during what is typically its dry season.
Flooding was also widespread during the 2011–12 La Niña. Much of inland southern and far northern Queensland, most of New South Wales, northern Victoria, and central Australia experienced flooding at least once between late November 2011 and March 2012.
See the timeline of events for more details on the widespread flooding across Australia.
Heavy rainfall during both La Niña events
2010–11 La Niña event
July 2010 to March 2011 rainfall deciles (based on climatology of gridded monthly rainfall analyses from 1900)
2011–12 La Niña
Well above-average rainfall
October 2011 to March 2012 rainfall deciles (based on climatology of gridded monthly rainfall analyses from 1900)
The two events combined
July 2010 to March 2012 rainfall deciles (based on climatology of gridded monthly rainfall analyses from 1900)