Climate Mixed-up spring
In its official spring outlook the Bureau of Meteorology (BOM) says there are roughly equal chances of a wetter or drier spring (September to November) for most of the country. Rainfall is likely to be below average for south-west Australia, but parts of south-east Queensland and far-east Gippsland have a slightly increased chance of being wetter than average.
On the temperature side, spring days and nights are expected to be warmer than average for the north and southeast of the country. However, clear nights mean the risk of frost will continue – particularly in areas with drier soils.
Following an unusually dry winter, near-median to low streamflows are expected for August to October – particularly in the south-east of the mainland, senior climatologist Robyn Duell says, adding: “Low flows are also forecast for the south-west and at some locations along the eastern seaboard.”
More specifically, near-median streamflows are more likely at 71 locations across Australia, with 56 locations set for low streamflows and 32 locations expected to be high to the end of this month.
Forecasts have not been issued for 22 locations due to very low model skill or missing observed data.
This past winter was largely dominated by clear skies, particularly inland across Australia, leading to dry conditions, cool nights and warm days, BOM climate prediction manager Dr Andrew Watkins says.
It was, in fact, the driest on record since the El Niño event of 2002-2003.
In terms of mean maximum temperatures, winter 2017 was the warmest on record, breaking the old 2009 mark.
Large areas of northern Australia observed record high mean maximum temperatures. Queensland, Western Australia, and the Northern Territory recorded the warmest maximums on record while winter days were the second-warmest on record for South Australia and third-warmest for New South Wales.
“We’ve just experienced a very warm and dry winter. In fact, daytime temperatures were at record-high levels across much of the country this winter,” Watkins says.
“These warm and dry conditions have meant fire potential in parts of eastern Australia has been unusually high this winter.
“Bushfires have already occurred in northern NSW and southern Queensland. In contrast, winter nights have been cooler than average in areas such as the Murray–Darling Basin.”
Looking ahead, Watkins says Australia’s main climate drivers – the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole – are both neutral at the moment, so other climate drivers are likely to influence spring.
“Warm waters in the central Indian Ocean may result in higher pressures south of Australia, resulting in more easterly winds, keeping the west drier than average,” he says.
In addition, higher pressures to the south of the continent will encourage more easterly flow across Australia.
In its latest ENSO wrap-up, the BOM says that international climate models suggest the tropical Pacific Ocean is likely to persist at ENSO-neutral levels until at least late 2017.
“Sea surface temperatures (SSTs) have cooled over much of the central tropical Pacific during the past several weeks, yet have remained within the neutral range,” it writes. “Other indicators of ENSO, such as the Southern Oscillation Index
(SOI), cloudiness near the Date Line and trade winds are also at neutral levels.
“The Indian Ocean Dipole (IOD) is neutral, though index values have generally been above zero for the past several months.
“Most climate models suggest a neutral IOD is likely to continue,” the Bureau says, adding: “However, two of the six climate models surveyed suggest a positive IOD may develop during spring.”
Positive IOD events are typically associated with below-average winter-spring rainfall and increased spring-summer fire potential over central and southern Australia. STREAMFLOW FORECASTS
The Bureau of Meteorology provides seven-day streamflow forecasts for more than 100 sites around Australia.
Combining near real-time rainfall and streamflow observations with rainfall forecasts, the BOM calculates how much runoff is likely, and flow of this water down the stream network.
These 7-day streamflow forecasts can be found at www.bom.gov.au/water/7daystreamflow
Spring will be bringing a wide variety of climate conditions to Australia, according to the Bureau of Meteorology Warm waters in the central Indian Ocean may result in higher pressures south of Australia, resulting in more easterly winds, keeping the west drier than average
Rainfall: Totals that have a 75 per cent chance of occurring for September to November. Source: BOM Temperature: The chance of above median maximum temperature for September to November. Source: BOM Photo: Southern Lightscapes-Australia/Moment/Getty Images