What can historical ‘mega droughts’ tell us about future water supply?

For hydroclimatologist Danielle Verdon-Kidd, a drought that happened more than a thousand years ago could provide important insights into Australia’s water future. 

In her work at the University of Newcastle, Verdon-Kidd studies how the climate has changed in the past to better understand how it might change in the future – and the impact this could have on water supplies.

“I also look at extreme event risk,” Verdon-Kidd said.

“Things like tropical cyclones that fill our water supplies, and droughts, where we have long-term perseverance of lower water supplies, which affects our ability to supply water for agriculture and potable water needs.”

The problem with studying drought in Australia is that official Bureau of Meteorology rainfall records only go back 120 years at best in populated regions.

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While the 13-year Millennium Drought is the longest on record, Verdon-Kidd said it’s possible Australia has experienced a mega drought, which typically last decades, and could experience one again.

“It’s something we haven’t got a record of in our instrumental data,” she said.

“Our rainfall records are … not long enough to capture the possibility of these longer droughts. But we know these mega droughts exist elsewhere in the world.”

Verdon-Kidd pointed to the Maya civilisation in Central America, which is thought to have collapsed due to a mega drought between 800 and 1000 CE, as well as areas of South Africa and North America.

In some cases there is a written record of these events, but in places like Australia scientists need to turn to natural archives.

This means looking at the thickness of layers within certain coral to get an indication of rainfall and sea surface temperature, or studying tree rings, which are large and healthy when climate conditions are good for trees, and become narrower when a tree is under stress. 

“There’s quite a range of these potential sources of information we can look at,” Verdon-Kidd said.

“These sources are giving us this history that we can link to the rise and fall of civilisations.”

However, she said Australia is behind when it comes to gathering paleoclimate information. This is partly because the country doesn’t have the same type of trees as more temperate regions, and so researchers need to find alternative natural archives.

Verdon-Kidd is currently investigating whether mangroves can be used to reconstruct rainfall and streamflow history in eastern Australia. 

Although the records are interesting in themselves, it’s not about doing science for science’s sake.

“I really want to make this work useful,” Verdon-Kidd said.

Once the researchers have reconstructed historical rainfall patterns using natural archives, they can run this information through water system models to see how current management practices would cope with past droughts.

“We can then play with that in terms of changing management options to see whether or not our water supplies are robust,” Verdon-Kidd said.

“It’s about having alternative water supplies during times of drought and mega drought.”