Drought confronts parts of Australia, ecologists are back on alert

Severe dry spells across parts of Australia have ecologists on both sides of the continent wary of the possible effects of warming climate conditions in the lead-up to summer.

While neither an El Niño nor a positive Indian Ocean Dipole (IOD) have been declared, the Bureau of Meteorology expects both will be confirmed towards the end of the year.

Regardless, it’s repeatedly warned Australians to expect hotter and drier spring conditions.

In its latest drought report, the BOM declared August to be the 10th driest since records began in 1900, with most of Queensland, New South Wales, Victoria and South Australia experiencing below-average rainfall.

That same report noted soil moisture for August was in the lowest 30% of readings.

It followed a July where much of southern Australia saw similar rainfall reductions, with severe shortages across WA’s southern coastal regions and parts of Australia’s south-eastern shores.

While the notion of drought is embedded into Australia’s collective psyche as a sunburnt country, there’s no single, official definition.

Meteorological drought refers to rainfall deficiency; a hydrological drought arises from a reduction in runoff, soil moisture, river and water storage levels; agricultural drought occurs when productivity and community income drops.

Regardless of how water dries up, prolonged deficits can be catastrophic for ecosystems and human communities.

And whether it be agricultural crops or native vegetation, plants are often the first in the drought firing line.

“If water becomes so limited that the plant can’t survive then, of course, it dies,” says Dr Joe Fontaine, an environmental academic from Murdoch University of lethal water deficits.

“Sub-lethal [water deficits] – maybe the plant grows less, or maybe part of it dies, like it lets go of some of its leaves, or part of its canopy, or a branch.”

Fontaine describes these consequences for plants as layers of an onion – degrees of dehydration that are exposed layer-by-layer until a plant is so water-deprived that it dies.

On the outside of the onion are the first signs of water deprivation, and they have consequences too.

“Maybe I’m not going to flower as much or make as many seeds. And that can have real flow-on effects to the whole system,” Fontaine says.

It goes without saying that a reduction in water can often mean fewer plant crops for human and animal consumption.

But ‘knock-ons’ might become particularly concerning in the event of a fire, particularly for native forests: fewer seeds to replenish a burnt population means reduced recovery and loss of food sources for animals.

“We spend a lot of time worried about black cockatoos in WA, which feed on plant seeds in trees, and maybe there’s less seeds for those cockatoos to feed on.”

Not at Black Summer levels, but dry conditions are still a concern

Parts of Australia razed during the Black Summer bushfires of 2019/20 endured prolonged drought conditions over three years, including record-low rainfall.

The opposite has been true for the past three years, with those same regions largely seeing record-high rainfall as a result of the ‘triple dip’ La Nina.

The eastern side of Australia has seen rainfall reductions, but not at the scale of Black Summer, or even WA’s current deficit.

But while it’s not at the extreme levels witnessed in 2019, experts are expecting a return to normal bushfire conditions in the upcoming warmer months.

“Yes, it’s dry, but I don’t think it’s dry enough to cause any sort of dynamic that we saw in 2019-20,” says Dr Rachael Nolan, a specialist in ecosystem disturbances at Western Sydney University’s Hawkesbury Institute for the Environment.

“[That] was after three years of dry conditions, we had three years for soil moistures to really deplete.”

While Nolan thinks widespread bushfires are less likely, she points to the likelihood of increased understorey vegetation on the back of three major wet years. Should low-lying vegetation like grasses, shrubs and tree seedlings dry out, it could act as fuel for bushfires.

“In terms of impacts on vegetation, I think there’s not going to be significant impacts, but in terms of fire risk, I think we’re looking at a return to a more normal fire season where there’s a good chance that we’ll see fires in some areas, as we often do in summer,” she says.

In WA, which has experienced much longer rainfall deficits on its southwestern coast, and is on alert for drier conditions brought about by a positive IOD, Fontaine is wary of the potential ecosystem impacts from a long dry spell.

He’s equally concerned by the risk of rising temperatures due to climate change.

“For every degree rise of temperature, the plants use water at twice the rate, so the water demand of the plant to keep its leaves, cool – transpiration –goes up exponentially with temperature,” he says.

“So water availability is a big deal, and it gets to be an even bigger deal as the temperatures [get] higher. These issues are really coupled in that the water’s going down, the temperature’s going up, which means the planets actually require more water.”