Welcome to the Climate and Water Outlook for summer 2015–16.
It’s now been six months since El Niño became firmly established in the Pacific Ocean.
This is a good time to take stock of the impacts so far, then look ahead to what may drive
our climate over summer. El Niño locked in during May as Pacific Ocean
temperatures approached one degree above average, raising the chances of a dry 2015.
But very warm conditions in the Indian Ocean have been countering the worst of El Niño’s
impacts. As a result, while some areas were certainly
dry, others had sporadic rainfall until August. And by September, a positive Indian Ocean
Dipole—similar to El Niño but in the Indian Ocean—had become established.
The combination of El Niño and a positive Indian Ocean Dipole provided a 'double whammy'
of drying influences for Australia. This meant the tap turned off—right at a
critical time in the southern growing season. But late October and early November saw rain—up
to a month's worth in one week in some places. While this rain was welcome, it hasn’t broken
the drought. Areas of long-term rainfall deficiency have
expanded over the past several months and now affect every State.
Some areas now need around eight times as much rainfall as they’ve seen in the past
month to lift them above drought thresholds. El Niño has also meant temperatures were
above-average over the last six months. October was the warmest on record for Australia.
Victoria’s maximum temperatures were nearly six degrees above normal—the most above-average
month for any State on record. With higher temperatures and evaporation,
plus little rain, soils are now very much drier than average.
Winter–spring is the time when southern water storages normally refill.
But dry and warm conditions have meant a very early end to the filling season. Inflows were
very much below average, and many storages are now less than half full heading into summer.
So what's driving Australia’s climate? El Niño is still strengthening, with current
temperatures in the Tropical Pacific comparable to the strongest El Niño’s on record.
History and climate models suggest El Niño will peak by the end of the year.
Of the 26 El Niños since 1900, only three have been followed by another El Niño the
next year. Ten have flipped into La Niña, and 13 have
eased to neutral. Most of the stronger El Niños have seen some
wetter periods near their end. This year’s positive Indian Ocean Dipole—and
its drying influence—has already started to break down.
In contrast, the sub-tropical Indian Ocean is expected to stay warm, feeding more moisture
towards Australia. So what’s the outlook for December to February?
Rainfall is likely to be average to above-average for most of the country, but a later start
to the wet season rains is expected in the north and northwest.
Our rainfall outlook has moderate accuracy at this time of year.
The streamflow forecast for November to January shows low flows more likely at 106 of 108
locations. No sites have near-median flows forecast,
and only two are likely to have high flows. Accuracy for our streamflow forecasts is high
at this time of year. The temperature outlook for summer is for
average to warmer-than-average days for most of Australia.
Nights are also likely to be average to warmer than average across most of the country.
Accuracy for this outlook is high at this time of year.
After poor spring rains and early heat, the Bushfire Outlook has been updated.
Areas of above-normal bushfire potential have expanded in South Australia and Tasmania.
So in summary: El Niño is expected to ease in early 2016.
Odds favour average to above-average summer rainfall for most of the country; but drier
in the far north and northwest. Low streamflows are likely.
The risk of bushfires is raised in an El Niño summer.
For more details, head to our website at bom.gov.au/climate/ahead You can also follow us on Facebook and Twitter.
Our next video will be released on Thursday 17 December.
For the Bureau of Meteorology, I’m Paul Feikema.