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El Nino is an ocean and atmospheric phenomenon that has a significant impact on our planet's weather.

How is El Nino shaping up for 2015/16?

How is the 2015/16 El Nino shaping up?

  • El Nino is now near its peak, although likely to persist well into 2016
  • It is likely to rank in the top three events in the last 50 years
  • Although it was predicted to match the 1997/8 event, it is currently falling short of both the 1997/8 and 1982/3 events dubbed 'super-El Ninos'
  • On average an El Nino summer brings below-average rainfall across northern Queensland, and a slight drying influence across the south-east of Australia, while inland Western Australia often sees above-average rainfall.
  • Meanwhile the Indian Ocean dipole has broken down, but sea surface temperatures are warmer than average. This could provide extra moisture for rain systems across Australia.

Source: Australian Bureau of Meteorology December 2015

While an El Nino event influences the whole world, the main effect is on the Pacific area, especially Australia, Indonesia and south-west America.



"In the US, in California they experience flooding during El Nino events."


The two strongest El Ninos that we know of were in 1982-83 and 1997-98.

Dubbed "super El Ninos", both these events had significant global impacts.



The 1982 El Nino caught countries around the Pacific completely unaware and prompted data gathering and research that lead to our current understanding of El Nino, Dr Cai said.

What causes an El Nino?


The shift from normal — or neutral — conditions to an El Nino (or its opposite — La Nina) is governed by a complex combination of atmospheric and oceanic events.




During an El Nino the temperature gradient is reduced, and the water in the eastern Pacific is warmer than normal.

But what causes an El Nino to start "is the subject of debate," Dr Cai said.





During El Nino the SOI is negative, as Tahiti has a lower air pressure than Darwin. This air pressure pattern is associated with wetter weather in Tahiti and drier weather in Australia and the western Pacific.

Frequency and severity

Scientists now have a very good idea of how El Nino will be affected by climate change, Dr Cai said, and it is not looking great.

"Under climate change the frequency of extreme El Nino events will double - to one every 10 years".


Another important factor in understanding the severity of an El Nino in Australia is the Indian Ocean dipole, a measure of sea surface temperature difference in the Indian Ocean.




A positive Indian Ocean dipole often occurs with an El Nino, which can magnify the impact, although they can also occur independently.

"In 1997 we had an Indian Ocean dipole in November and in January '98 we had the biggest El Nino," Dr Cai said.



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