The overall effect of this El Niño on Australia was weak to moderate, with the 13 months from April 2015 to April 2016 (Figure 1) resulting in widespread areas of below average rainfall across central to southern Queensland, southeast South Australia, Victoria, and Tasmania. Dry conditions were already in place in Queensland and southeastern Australia in the lead up to this El Niño.
After sea surface temperatures in the central tropical Pacific Ocean came close to El Niño levels in 2014, the central tropical Pacific Ocean was primed for El Niño in 2015. Westerly wind events in January and March led to rapid ocean warming during autumn 2015, reaching El Niño levels during mid-April. Further westerly wind bursts consolidated the event in May and June. Rainfall was below average over parts of eastern Australia during April to August 2015 (Figure 2), although very warm sea surface temperatures (SSTs) in the eastern Indian Ocean may have offset some of the drying effect of the El Niño pattern in the Pacific. Warmer waters in the eastern Indian Ocean may provide extra moisture for rain-bearing systems as they cross Australia.
Between late August and mid-November a positive Indian Ocean Dipole (IOD) developed, further suppressing rainfall over much of Australia. The combination of the positive IOD and El Niño saw widespread below average rainfall during September and October 2015 (Figure 3). Rainfall was the equal fourth-lowest on record for Australia during September, and Tasmania had its driest spring on record. Mean temperatures for Australia were also highest on record for October to December 2015.
Below average rainfall persisted over much of eastern and northern Australia during the first four months of 2016 (Figure 4), with large parts of the northern coastline recording rainfall in the lowest 10% records. The event finally broke down during May 2016.
Peak values of central tropical Pacific SSTs and NINO indices exceeded +2 °C, placing this event alongside 1982 and 1998 as one of the strongest events on record. NINO3.4 reached +2.5 °C in November 2015.
This very strong El Niño contributed to an early start to the 2015–16 southen fire season, a markedly drier than average northern wet season, the weakest and least active tropical cyclone season on record (record low 3 TCs in 2015–16 season, none reaching category 3 strength), and prolonged heatwaves across Australia during autumn 2016. As the event started to break down very warm ocean water was pushed towards Australia. Combined with a delayed monsoon and cloudless skies this resulted in the worst coral bleaching event on record for the Great Barrier Reef. For more information on the effects of this El Niño see Climate Update El Niño is over, but has left its mark across the world.