Is Australia Ready for a 20-Year Megadrought?

What is a drought?

This may seem an easy question. You may be thinking something like ‘a time when it rains less than usual’. But let’s dive a bit deeper. For how long does it need to rain ‘less than usual’ before a spell of dry weather becomes a drought? How much less than usual does it need to rain over that time? If you are a tree with deep roots, for how long does it need to not rain before you even notice? How does that differ if you’re a fish reliant on fast-flowing freshwater? Or a citrus farmer in the Australian Riverina?

In fact, Australia has an extremely variable climate, and it’s likely that long periods of dry weather have been part of Australia’s climate for millennia. In the absence of disturbance, Australia’s natural environments are well-adapted to low rainfall. But since the European invasion of Australia, droughts have been defined largely by their impacts to agriculture and municipal water supply—and in that sense, Australia ranks fifth in the world for economic damage caused by drought.

Australian droughts and climate change

Because of climate change, when and where rain falls across Australia is changing—with impacts on both natural environments and Australian businesses and society. For example, south-eastern Australia recently experienced its most intense drought on record: the 2017-2019 ‘Tinderbox’ drought. The Tinderbox drought cost Australia ~$53 billion, set the conditions for the 2019/2020 Black Summer bushfires, and caused mass fish deaths in rivers already degraded by human mismanagement. Rainfall deficits during the drought were so extreme that climate model simulations of the historical period are unable to reproduce them.

On which note: model simulations of future drought change in Australia are uncertain. That is, based on the model projections we use to understand Earth’s future climate trajectory, we don’t know how or even if Australian droughts will change. Without understanding the range of drought lengths and intensities Australia could face in the future, we cannot be adequately prepared.

A holistic approach to understanding Australian drought

One way to be prepared is to take a holistic approach to understanding Australian droughts: understanding both the full possible range of natural variability in Australian droughts and how this is changing because of climate change. This is how Dr Georgy Falster, a DECRA Fellow recently started at The University of Adelaide, approaches her drought research. She draws information from multiple sources (weather observations, model simulations, natural archives like tree rings and ice cores), which lets her make holistic assessments of Australian drought characteristics in the centuries before climate change began. She compares these with the handful of droughts experienced in the past century to determine how droughts are changing, and what we might therefore expect in the future.

Potential for Australian ‘megadroughts’

Dr Falster’s recent research using climate model simulations of rainfall over the past millennium found that on average, modern droughts in south-eastern and eastern Australia are already probably slightly longer on average than they were in the pre-Industrial (the study is outlined in this Conversation article).

Maybe more alarmingly, the models also suggest that natural variability in Australian rainfall can produce ‘megadroughts’ lasting 20 or more years. It is simply luck that we have not experienced one of these megadroughts in the past century. But when a megadrought inevitably hits Australia, it will be against the backdrop of human-caused climate change. Droughts occurring in today’s warmer world can be intensified by both changing large-scale weather patterns, and soil that is more easily dried out (the latter is exacerbated by removal of natural vegetation for farming).

Over the next few years at the University of Adelaide, Dr Falster’s research will dive more deeply into the conditions that could make Australian megadroughts more likely—including the influence of the Indian and Pacific oceans. She will produce long tree ring-based records of Murray-Darling Basin rainfall to see if there were any megadroughts (or anything else interesting!) in the centuries before we have rain gauge data. She will place her findings in a broader context through detailed analysis of both climate models and a global network of centuries-long rainfall records from tree rings and other natural archives. With these analyses, she hopes to quantify when exactly we should expect a megadrought to arrive on our shores: whether that might be in the coming centuries, the coming decades, or the coming years.

Finally, it is important to remember that drought is not inherently a disaster. Disaster only occurs when we are not prepared for the length or intensity of a particular drought. If we can quantify the full range of drought lengths and intensities that Australia could face in the future, then the relevant authorities can have management plans in place—across domestic water supply, support for farmers and rural communities, support for Australian businesses, and adequate protection for natural environments.