IT’S official. El Niño is back and it’s not good news.
The Bureau of Meteorology has confirmed what climatologists have been debating for months – that the warming of sea surface temperatures in the central and eastern Pacific Ocean has begun.
And it’s a little early.
The last time an El Niño event was declared was five years ago. And they generally occur between June and November.
The news is not great for Australia’s drought-stricken farmers.
El Niño is generally the precursor for drought, as it causes reduced rainfall in winter and spring in the eastern states.
It also causes warmer than average daytime temperatures over the southern half of the country.
Sea surface temperatures have been at, or near, El Niño thresholds since spring last year, save for a brief dip soon after Christmas.
Just four weeks ago, the bureau raised its El Nino Southern Oscillation (ENSO) tracker to the “alert” level, raising to 70 per cent or greater its expectation an El Niño would form in the Pacific in the winter or spring of 2015.
Wide areas of Queensland, NSW, Victoria and South Australia are in severe drought going back more than two years.
Assistant Director for Climate Information Services, Neil Plummer, said while the El Niño is forecast to strengthen during winter, the strength of an El Niño does not necessarily correspond with its impact on Australian rainfall.
Australia experienced one of its worst droughts during a weak El Niño in 2006–07, while stronger events such as the El Niño event in 1997–98 had only a modest impact on Australian rainfall.
“Recent significant rainfall and flooding along the east coast of Australia, associated with two almost back-to-back East Coast Lows, did not penetrate far into inland regions and therefore have done little to alleviate conditions in drought affected areas,” Mr Plummer said.
David Jones, of the bureau’s climate information services branch, says forecast models from around the world suggest the El Niño will probably have a significant impact.
“What those models show is that the current El Niño event is likely to see us get increased intensity around about spring into early summer,” Dr Jones said.
“You know, there’s always a little bit of doubt when it comes to intensity forecasts, but across the models as a whole we’d suggest that this will be quite a substantial El Niño event.
“Certainly the models aren’t predicting a weak event. They are predicting a moderate-to-strong El Niño event. So this is a proper El Niño event, this is not a weak one or a near miss as we saw last year.
WHAT IS AN EL NINO?
* A warming of sea surface temperatures in the eastern and central Pacific Ocean that disrupts weather patterns across the Pacific.
* Can cause a corresponding cooling of the ocean in the western Pacific and around Northern Australia
* Cooler seas near Australia, Papua New Guinea and Indonesia reduces convection – moist air at the surface that is heated, rises, cools and condenses into rain-bearing clouds.
* Convection migrates towards the eastern Pacific and can deliver increased rain to the west coast of North and South America * El Niño can disrupt the trade winds that, in the southern tropical Pacific, blow moisture-laden air towards eastern Australian coast
WHAT ARE THE EFFECTS OF AN EL NINO IN AUSTRALIA?
* El Niño increases chances of below-average rainfall through winter and spring in much of Australia, especially the north and east
* El Niño does not always mean drought but nine out of the 10 driest winter/spring periods happened in El Niño years
* Australia’s severest droughts – 1982/83, 1994, 2002 and 2006 were all associated with El Nino * Since 1900, El Ninos delivered winter/spring rainfall 28 per cent lower than the long-term average
* Warmer-than-average weather, particularly in southern Australia and particularly in the second half of the year.
Decreased cloud cover increases surface heating and assists to keep rainfall low
* Background warming of the atmosphere has made El Niño years warmer since the 1950s, the Bureau of Meteorology says
* In warmer months, El Niño can cause fewer slow-moving “blocking” high pressure systems, worsening heat extremes for cities such as Adelaide and Melbourne with an increase in extreme hot days and heatwaves further north
* Frost increases in El Niño years in cooler months in eastern Australia because clearer skies contain less daytime heat and lead to reduced minimum temperatures
* Between 15 and 30 per cent more frost days in El Niño years than average in northern Victoria and southern NSW, affecting agriculture
* Australia’s record low temperature of -23C at Charlotte Pass, NSW, on June 29, 1994, occurred during a strong El Niño
INCREASED BUSHFIRE RISK:
* El Niño droughts dry the bush and have led to disasters including the 1983 Ash Wednesday bushfires that killed 71 people in Victoria and South Australia.
DISRUPTED TROPICAL WEATHER:
* Fewer tropical cyclones, especially for Queensland
* Later onset of northern monsoon rains
* Below-average wet season rains early in the season, with average rain later in the season
REDUCED WINTER SNOWFALL:
* The four lowest recorded peak snow depths in Australia’s alpine country occurred in El Niño years, including severe drought years in 1982 and 2006