El Niño rears its ugly head again

El Niño rears its ugly head again


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Australia's big dry is likely to continue over summer with both El Niñó and Indian Ocean Dipole positive events likely to form. Both events are correlated with drier than average conditions, especially when both occur simultaneously.

Australia's big dry is likely to continue over summer with both El Niñó and Indian Ocean Dipole positive events likely to form. Both events are correlated with drier than average conditions, especially when both occur simultaneously.

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The BOM has raised the likelihood of an El Niño forming. Combined with an IOD positive event it looks like a dry summer ahead.

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LIKE an unwanted house guest who keeps rocking up on the doorstep, an El Niño weather event is again on the cards according to the Bureau of Meteorology (BOM).

In their most recent El Niño Southern Oscillation (ENSO) update, put out fortnightly, the BOM raised the ENSO Outlook to El Niño alert.

This means there is around a 70 per cent chance of El Niño occurring before the end of the year, around triple the normal likelihood.

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It comes just after farmers breathed out a sigh of relief on reading the previous ENSO update, where the BOM downgraded the risk to an El Niño watch, with a host of models used by the agency downgrading the odds of an event forming.

Further adding to the likelihood of a long and hot summer is the chance that in the Indian Ocean, a positive Indian Ocean Dipole (IOD) may have started.

In worrying news for drought impacted farmers, the BOM said when combined, these two events in spring increase the possibility of a dry and warm end to the year.

It also raises the risk of heatwaves and bushfire weather in the south.

In terms of the climate drivers leading the push towards El Niño, the tropical Pacific Ocean has warmed in recent weeks due to weakening of the trade winds, while the Southern Oscillation Index has fallen to typical El Niño levels.

In the Indian Ocean, there are signs that a positive IOD is currently underway. The IOD index has exceeded the threshold (+0.4 °C) for the last four weeks.

To be considered at true IOD positive event statistically these values must persist until November.

That is on the cards according to the models used by the BOM, with the outlook suggesting positive IOD values are likely to continue through the spring, before returning to neutral values in late November to December.

The BOM outlook comes just after it released data confirming the extent of the dryness through September.

It said this September was the driest on record, increasing longstanding rainfall deficiencies in drought impacted eastern Australia and hurtling southern Australia towards a similar predicament.

The BOM data showed the month was especially dry across the southern mainland.

Many parts of Victoria recorded their lowest September rainfall on record, with a number of north-western centres not recording 5mm for the month, compared to a long-term average of 20-50mm.

It all added up to the month being the driest September on record nationally, and the second driest September on record for Victoria, third driest for Western Australia, and fourth driest for South Australia.

It was a marginally better result in other parts of the country but not enough to make up the deep rainfall deficit.

Compared to other January to September periods since 1900, year-to-date rainfall has been the second lowest on record for the Murray–Darling Basin, third lowest for New South Wales, and eighth lowest for Victoria.

Accompanying recent low rainfall have been unusually high day-time temperatures, which add to the impact of reduced rainfall, e.g. as seen through reduced soil moisture.

Australian maximum temperatures for 2018 to date have been the second warmest on record with an anomaly of +1.36 °C (behind 2013 with an anomaly of +1.54 °C).

Both New South Wales (+2.17 °C) and the Murray–Darling Basin (+2.10 °C) have experienced their warmest January–September period on record.

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