Ian Mannix
Cosmos newsroom
Scientists are warning about rapidly changing weather patterns across the globe which can bring winter droughts, bushfires and heatwaves to normally wetter regions like far north Queensland or western Tasmania.
They’ve termed the phenomena “flash droughts.”
Professor Albert van Dijk from the Australian National University (ANU) Fenner School of Environment and Society and lead author of a new report on global water availability released today, says flash droughts are “analogous to a flash flood.”
“A flash drought is an unexpectedly rapid development of drought conditions,” Van Dijk tells Cosmos.
“They usually go hand in hand with prolonged heatwaves. When very low rainfall combines with very high temperatures and dry air it can cause very high evaporation rates and rapid drying out of soils and lowering water levels.”
They are called flash droughts because they develop much faster than a ‘normal’ drought: within weeks or a few months, depending on the climate.
Flash droughts are mostly noticeable in somewhat humid regions with a winter or cool season, like much of Europe.
In the past, the summer in those places was too short to produce droughts of the severity seen now. But with much higher temperatures, droughts develop to a point that wasn’t reached as quickly in the past.
Van Dijk says that in Australia, flash droughts have so far most clearly been recognised in the form of unusually or unseasonably rapidly developing bushfire risk situations in normally quite humid regions or seasons.
“Across much of Australia, high temperatures and a lack of rainfall are quite common thanks to its extremely variable rainfall by world standards. So often we probably wouldn’t really speak of a flash drought.
“In fact, in most of Australia, it takes more than one year of drought to really be noticed. However, there are exceptions, like Tasmania and along the wet east coast, where we have seen the impact of much higher temperatures lead to more rapid drying and, especially, cause more and more severe bushfires.
“The 2019-20 bushfires are a good example where the east coast quickly dried up and the fire season started almost in winter.
“We may see flash droughts impact on ecosystems and crops that are used to regular rainfall, say in far north Queensland or western Tasmania, for example.
“The burning of centuries-old trees in the Tasmanian highlands and in the normally wet Gondwana forests in the QLD-NSW border area in the 2019-20 forest are an example of what we can expect to see more of with drier, hotter and longer heatwaves on the horizon.
“It is also likely that winter cropping in the southern states is becoming even more unreliable than it already was.”
Previously in Cosmos Very wet and very dry
Van Dijk is lead author on a first-of-its-kind report released by the Global Water Monitor Consortium, led by the ANU.
According to the report, the third La Niña year in a row intensified existing droughts in the Americas, while causing floods in parts of Asia and Oceania.
The report found global warming is changing the water cycle across the planet, while also warning that events like “flash droughts” will become more frequent in the coming years.
Globally, in 2022 the water cycle was dominated by relatively warm ocean waters in the western Pacific and the eastern and northern Indian Ocean. As a result, a severe heatwave developed in South Asia early in the year, followed by a very wet monsoon that caused massive floods in Pakistan.
Elsewhere, in Europe and China, extreme heatwaves gave rise to these so-called ‘flash droughts’ causing low river flows, agricultural damage and bushfires.
The report shows that air temperature over land in 2022 followed the long-term warming trend, while air humidity is declining. “This means that nature, crops and people will need more water to stay healthy, which compounds the problem,” says Van Dijk.
“The jury is still out on whether those three La Niña years were a statistical fluke or the first signs of something more sinister,” says Van Dijk.
“If La Niña or El Niño patterns are going to stay around longer in future, that is going to cause a lot of trouble, with worse, longer droughts and worse floods alike.”
The Global Water Monitor is a joint initiative of several public and private research and development organisations. All underlying data are publicly available here.