El Niño has arrived, it’s getting stronger, and it’s not about to go away soon. And already there are rumblings that this could be a big one. El Niño in Australia means warmer temperatures, and sometimes, but not always, drier conditions.
In 2014, some climatologists thought a big El Niño might have been on the cards. Ultimately, after some vigorous early warming in the Pacific, conditions only touched on El Niño thresholds. This year, with an event already established, climatologists are suggesting the odds are rising of an El Niño rivalling the record events of 1982 and 1997.
So what’s all the fuss about, and how are conditions different from last year?
El Niño events are identified by equatorial Pacific Ocean temperatures. At the ocean surface, an El Niño is when these are sustained at about 0.8°C warmer than average. As we speak, temperature anomalies are exceeding twice that value.
In fact, we have just experienced twelve consecutive weeks with temperatures more than 1°C above average in all five of the key El Niño monitoring areas. The record was previously held by the 1997 El Niño, when this widespread warming lasted eight consecutive weeks.
But no two El Nino’s are exactly the same. Despite this warming in the tropical Pacific Ocean, in the Indian Ocean temperatures are far warmer than they were in 1997 (or 1982), which may mean different impacts for Australia. But more about that later.
When sea surface temperatures in the central equatorial Pacific get warm enough, the atmospheric circulation shifts and the usually strong trade winds reduce, sometimes even reversing.
The direct consequence of the changing wind pattern is that the sea level in the western equatorial Pacific is no longer “piled up” by the trade winds. Low sea levels north of New Guinea (shown boxed) are strongly correlated with Nino3.4, which is the index that relates best to Australian climate.
At the peak (December) of the 1997 El Niño, the sea level in the western Pacific dropped nearly 30 cm. It is only August and already the sea level is nearly 25 cm below normal to the north of Australia.
Likewise, in the eastern Pacific, sea levels have risen by similar amounts as the weakened trades allow water to shift east. This half-metre difference in the normal sea level between the east and west is a classic strong El Niño signature.
A drop in sea level often means less water flows past Indonesia and down Australia’s west coast — weakening the Leeuwin Current and reducing the likelihood of coral bleaching in Western Australia.
Climate forecast centres around the world are keenly monitoring the development of this year’s El Niño. Why? Because for some time, all the top dynamical (i.e., physics based) climate models have agreed that there is more warming of the tropical Pacific Ocean to come.
The current (late July) average forecast is for continued warming peaking at a Niño 3.4 value of +2.7°C by December. Such a value would put 2015 alongside the big El Niño events in 1982 (+2.8°C) and 1997 (+2.7°C).
Reinforcement by the atmosphere is an essential part of El Niño development – as you can see in our Understanding ENSO video.
Last year the ocean began generating an El Niño but the atmosphere wouldn’t come to the party. This year the atmosphere is clearly responding.
Two exceptionally large westerly wind events have already occurred in the western equatorial Pacific this year, giving this El Niño a significant boost. Another wind event is forecast for August to kick the system along even further and add to the strength of this El Niño.
Of the 26 El Niño events since 1900, 17 have brought widespread drought to Australia. In the big El Niño of 1982, drought devastated the eastern half of Australia and drove the devastating Ash Wednesday bushfires.
In contrast, the even stronger El Niño of 1997–98 brought more localised drought, with key rains in May and September meaning winter crops did reasonably well in most areas. Other years, such as 2002 and 1996, when weaker El Niño’s occurred, the drought was more severe.
For Australia, it’s not the size of El Niño that matters, it’s how it interacts with other rainfall drivers – such as sea surface temperatures around the continent and in the Indian and Southern Oceans, as well as random ‘weather noise’ – that governs the eventual rainfall over the continent.
A significant El Niño event is currently underway, and there’s a chance it could rival the big events of 1982 and 1997. While this may increase the chance of drought and higher temperatures in eastern Australia, many other factors influence potential impacts.
We are already seeing that in the August–October Bureau of Meteorology seasonal outlooks, with the warmest June ocean temperatures on record in the southern Indian Ocean keeping the strengthening El Niño at bay by putting more moisture into the mid-levels of the atmosphere and changing weather patterns.
So what’s the final 2015 El Niño prediction?
The 2015 El Niño is already significant, and a big El Niño certainly remains a possibility. Widespread strong impacts haven’t (yet) raised their head for Australia and indeed, such as in 1997, may never do.
But managing El Niño is all about managing risk. The southern spring is the time when dry weather, frosts and heatwaves can hurt farmers and many others the most. And that’s when El Niño events, which raise the odds of these impacts, like to bite hardest.
The authors will be one hand for an Author Q&A between 12:30pm and 1:30 pm on Tuesday, August 11. Post your questions in the comments section below.
Survivors of Cyclone Pam on the South Pacific islands of Vanuatu are bracing for a lack of food over the coming months because crops were destroyed in the recent storm.
Much of the archipelago’s population relies on subsistence farming and when the monster cyclone ripped through the country last week it wiped out livelihoods as well as homes.
“There’s always a lot of attention in the beginning, the first few weeks of a big disaster. But now, we’re looking at a hunger gap over the next three to six months,” said World Vision’s Emergency Operations Manager in Vanuatu, Alex Snary.
Aid agencies are rushing to deliver desperately needed supplies, especially to communities on the remote outer islands, which are still out of contact.
At least 11 people were killed in the disaster and 3,3000 displaced.
“It’s almost miraculous [on Tanna Island] that there isn’t a large number of casualties, given…
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Vanuatu’s President Baldwin Lonsdale says the tiny South Pacific island nation has lost much of its development due to the havoc wreaked over the weekend by “monster” Cyclone Pam.
“It’s a setback for the government and for the people of Vanuatu. After all the development that has taken place, all this development has been wiped out,” he told the Associated Press in Japan attending a U.N. conference on disaster-risk reduction. “We will have to start anew again.”
Lonsdale went on to say that climate change contributed to the devastation as the low-lying islands of the Pacific are suffering from rising sea levels.
International aid agencies along with military personnel from Australia, France and New Zealand have arrived in Vanuatu to assess the damage and deliver much needed aid and supplies.
Oxfam, who led coordination efforts in preparing for the storm, said 90% of housing in the capital, Port Vila, has…
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