03/06/2020

(AU) Australia Among Global 'Hot Spots' As Droughts Worsen In Warming World

Sydney Morning Herald - Peter Hannam

The world's major food baskets will experience more extreme droughts than previously forecast as greenhouse gases rise, with southern Australia among the worst-hit, climate projections show.

Scientists at the Australian National University and the University of NSW made the findings after running the latest generation of climate models used by the Intergovernmental Panel on Climate Change (IPCC). Future drought changes were larger and more consistent, the researchers found.

Southern Australia is already on a long-term drying trend and climate models suggest those changes will continue as greenhouse gas emissions rise. Credit: Alex Ellinghausen

“Australia is one of the hot spots along with the Amazon and the Mediterranean, especially,” said Anna Ukkola, a research fellow at the ARC Centre of Excellence for Climate Extremes and lead author of the paper published in Geophysical Research Letters.

For southern Australia, the shift to longer, more frequent and more intense droughts up to 2100 will be due to greater variability in rainfall rather than a reduction in average rainfall. For the Amazon, both mean rain and variability changes.

The researchers applied the sixth generation of the so-called Coupled Model Intercomparison Project (CMIP6), which will underpin the IPCC's Sixth Assessment Report due for release in a series from April. The latest iteration benefited from five years more observations which were used for comparison and to refine processes.

The models simulated a so-called "middle of the road" scenario for greenhouse gas emissions against a high emissions "fossil-fuelled development" one. Under the latter trajectory, average droughts would double in length from two to four months by 2100 compared with the 1950-2014 period.

“For regions that have quite a lot of agriculture [such as North America and parts of China and Europe], the models suggest they will have more intense droughts in the future even though they may not experience changes in mean rainfall," Dr Ukkola said. “We don’t see any regions where intensity will decrease in the models."

Dry times ahead: a parched Macquarie River tributary within the Macquarie Marshes of north-western NSW in August last year. Credit: Wolter Peeters

One reason for the prediction of worse droughts is that the latest models assume the climate will respond more than previously understood to increased atmospheric levels of carbon dioxide and other greenhouse gases.

Some of the models used for CMIP6 predict changes of more than 7 degrees in global and Australian temperatures by the end of the century.

Australia's vulnerability to big shifts in annual rainfall already challenge the country's farming sector, while also leaving much of the country's south more at risk of bad bushfire seasons - such as last summer's - as forests dry out.

The CSIRO has long forecast a large reduction in stream flows in the Murray-Darling Basin, for instance, as reduced cool-season rainfall combines with higher temperatures. Such a trend appears to have already begun.

While a more moderate emissions trajectory will still produce more intense, frequent and longer lasting droughts in most of the world's mid-latitude regions than current conditions, the shift will be less than if carbon emissions remain near the top of forecasts.

"You are never every worse off with a 'middle-of-the road' course of emissions than a higher one," said Andy Pitman, director of the Climate Extremes centre, and one of the authors of the report.

"You are better off if you don't pump up the damn stuff in the first place," Professor Pitman said.

Rainfall variability, already a feature of Australia's climate, will likely get worse with climate change, climate models show. Credit: Nick Moir



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