That old bit of bush wisdom about floods following drought may not be completely accurate, but there’s truth in it, which is apparent in the three-month climate outlook to April.
After a long run of more-or-less dismal forecasts for farmers in southern Australia, the Bureau of Meterology is heralding a cool, damp transition from summer to autumn for much of south-eastern Australia.
The drought-followed-by-flood myth has a degree of support in the climate records, which show that for southern Australia, strong El Nino events often collapse into wetter-than-normal periods.
About 40 per cent of El Ninos have moved directly into the wet La Nina phase, and the odds of that happening seem to be at least doubled after very strong El Ninos.
BoM’s Climate Services manager, Dr Andrew Watkins, was gratified to report that the POAMA model used to built the Bureau’s three-monthly outlooks has produced a February-April 2016 rainfall map that correlates strongly with composite maps of actual rainfall following strong El Nino breakdowns going back to the early 1970s.
But what the wetter-than-average prognosis actually means for farmers remains to be seen, Dr Watkins said. Soil moisture deficits in some areas of southern Australia are so acute that significantly better than above-average rainfall will be needed to restore the balance.
The three-monthly forecast is reinforced by continued record warmth through the Indian Ocean, which is important for streaming moisture-laden air across the Australian continent.
For northern Australia, the outlook is less compelling.
Although the Wet arrived on time and produced some good one-off falls, the time between monsoon breaks has been lengthy and failed to deliver the moisture the north is looking for.
This is typical for an El Nino, Dr Watkins said, as is the low number of tropical cyclones. In 2015-16, “low” so far means none.
Since the mid-1970s, the only year that January has passed without a cyclone in Australian waters was 2006-07, also an El Nino year.
A tropical low is threatening to form into a weak cyclone in the last days of January, but the sort of cyclone that crosses the coast and collapses into a rain-bearing depression over Queensland remains elusive.
That’s not to say it won’t happen, Dr Watkins said, and he advised northern residents not to relax cyclone vigilance until the season is well and truly over.