If you are thinking your fields filled with deep moisture after 3 years of wet weather conditions are well placed to cope with the looming long, hot summer, think again. It could take just weeks of hidden heat to undo all that good.
Australia has always been a country of extremes, but those extremes are getting… more extreme. And that’s added a new term to our weather lexicon: “flash drought”.
“We’re very familiar with climate flip-flops here in this country, from droughts to flooding rains and back again,” says Monash University Associate Professor Ailie Gallant. “But how does this transition actually happen?”
The National Environmental Science Program’s Climate Systems Hub has been assessing the implications of an accelerated shift to an El Niño weather pattern after 3 La Niña years. Gallant is part of the hub’s Extreme Climate research project.
She says their research demonstrates that under certain conditions, some sodden soils can dry out in weeks, and that has dire fallout effects for bushfires and the impact of heatwaves.
“Some of the drying that we’re seeing, anecdotally, people are talking about it coming on very quickly.”
In October 2022, analysis showed the root zone soil moisture (generally about 1m deep) across most of Australia was much wetter than usual. In October 2023, many of those same sensors showed the soil to be much dryer than average.
The effect of a lack of rain is simple, Gallant explains. We notice the absence of the puddles and mud which indicate the soil is moistening.
But another process kicks in when the rain stops, one that’s far less visible – soil evaporation.
Combine warmer-than-average temperatures with clear, dry skies and you get the opposite of a perfect storm.
“The atmosphere becomes more thirsty, it has high evaporative demand. So that means the landscape can start to dry out – and dry out quite quickly,” Gallant adds.
And the pattern everybody expects and is prepared for – where a drought follows the traditional pattern of building up over several months – goes out the window.
“You might have heard of the term flash flood before, but if you haven’t heard of flash drought, this is a drought that can come on quickly… within around 1 month or less,” Gallant explains. “So you get this period of rapid drying descent into very, very dry conditions. So when I say very dry conditions, we’re talking soil moisture in the lowest 10 or 20% on record.”
September to October 2023 appears to have met that criteria. Rapid drying “hotspots” were evident in central eastern Australia, parts of southern Australia, southwestern Western Australia and Northern Australia.
“But flash droughts can also be flashy because they don’t last a long period,” Gallant says. Research indicates they typically linger around 40 to 60 days. But not always.
“We saw a couple, for example, in the Wimmera region of western Victoria that lasted upwards of 3 months. And 1 or 2 that lasted for 6 months. So, in that sense, flash droughts aren’t necessarily flashy. They don’t always flash on and off. But they can flash on quickly,” she explains.
Gallant says the Climate Systems Hub is now working to assess the “on the ground” impact of flash drought on agriculture, environments and regional communities, and what regions are most vulnerable.
“One of the things we’re focusing on at the moment is identifying flash drought or rapid drying hotspots,” she states. “There seem to be places where it happens more than other places.”
Initial indications point to southwestern WA, large parts of the Kimberley Ranges, the northern NT and Queensland, and an inland band extending through Queensland, Victoria and southern South Australia. Western Tasmania appears to be a particular “hotspot”.
“This plot is just very preliminary data,” warns Gallant. “So please do take it with a grain of salt. We’re really asking questions around what the lifecycle is for periods of rapid drying and any associated flash drought that might happen, and how this varies across Australia.”.
The Greenlight Project is a year-long look at how regional Australia is preparing for and adapting to climate change.