WESTERN AUSTRALIA: Hidden history of megadroughts captured in ancient tree rings and the study has also suggested the region was comparatively blessed with rain during the 20th century according to Climatologist Alison O’Donnell said rainfall records since 1900 capture “one of the wettest periods in the last 700 years”.
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“The worst drought periods that have occurred in this region occurred prior to instrumental records,” she said: Dr O’Donnell from the University of Western Australia and her team were able to piece together a record of droughts and floods back to the year 1350 by looking at tree growth rings from a stand of ancient trees she found on the edge of a salt lake.
“We removed little cores of wood that are about the size of a drinking straw, which allows us to look at the rings that are in the wood without causing any damage to the tree.
“The trees easily heal over those little small holes that we put in the trunk,” she said.
“We can measure the rings and determine from how wide they are, how much rain fell in each year that the rings grew.”
A record of megadroughts
Dr O’Donnell discovered the Wheatbelt experienced a pair of 30-year droughts, far more severe than any seen since European settlement, in the 1760s and then again in the 1830s.
“There were some wet years within that 30-year period, but on average the rainfall was really quite low compared to the long-term average over the last 700 years,” she said.
“The variability of rainfall in this region is actually a lot higher than anyone could have thought.
“Droughts are a lot more common than we think they are.”
Extending Australia’s climate history
As scientists try to tease apart human-caused climate change from natural variability, one of the biggest challenges has been the short 121-year period of the instrumental climate record kept by the Bureau of Meteorology.
Climatologist Nerilie Abram, from the Australian National University, said scientists are still piecing together Australia’s past climate.
“Australia as a whole is fairly underrepresented in terms of what we know about past climate variability,” Professor Abram said.
“But in south-west Australia particularly, we haven’t had a record like this in the past.”
Up until recently, most research on Australia’s historical climate has focused on eastern Australia, where written records, tree rings and even coral have been used to reconstruct the climate back to 1788 and beyond.
Researchers Linden Ashcroft, Joelle Gergis and David Karoly have even been able to reconstruct a record of the so-called “settlement drought” which struck the first fleet in 1791.
A heatwave struck the colony in the summer of 1791, after which one settler wrote “birds dropped dead from the trees, and almost every green thing was burnt up”.
By the end of that year, ships were sent to fetch water for desperate colonists.
The drought lasted through to 1793, when it was reported that “the rain of April came too late to save the Indian corn of the season, which now wore a most unpromising appearance”.
The tree ring studies have shown this event was experienced across all of eastern Australia and was not restricted to the immediate Sydney region.
Extending WA’s climate history
Recently discovered written weather observations from the Perth region have enabled Dr Gergis and Dr Ashcroft to reconstruct the climate of south-west Australia back to the 1830s.
“We show dry conditions in the late 1830s until early 1840s,” Dr Gergis said.
“We note that this period was also dry in south-east Australia from our previous work.
Professor Abram said the tree ring study provides another layer of proof for the 1830 drought.
“[It] appears to correspond quite well with one of these drought intervals that have now been detected in the tree ring record,” she said.
Future could be even drier
South-west Australia is already in the midst of a drying trend considered to be one of the strongest impacts of climate change globally.
Rainfall in the region has declined by more than 20 per cent since the 1970s.
The researchers say given the tree ring study shows megadroughts can occur in the region even without the drying impact of climate change, the future for south-west Australia’s water resources could be even more severe.
“Based on the instrumental record alone, our understanding of how bad droughts can get doesn’t fully capture what is actually possible,” Dr O’Donnell said.
“These results indicate that we might even expect worse droughts than are currently projected for the region using climate simulation models.”
#AceNewsDesk report …,Published: May.27: 2021:
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