Thu. Jun 30th, 2022

Scientists believe the Northern Territory may have had a much drier past, warning that if it continues to hand out unprecedented water allocations based on current data, there could be “major environmental and cultural damage”.

Tree rings from the Katherine region have provided researchers with a rare glimpse into data dating back almost 600 years that shows rivers have not always flowed at the rate they do today – in fact, they flowed at much lower levels.

“The last few decades have been the wettest that we’ve seen in 600 years,” UNSW Associate Professor Fiona Johnson said.

“The Northern Territory has some of the wildest and most pristine rivers in the world historically, and we can see what goes wrong in other parts of Australia where water has been over-allocated.

“There are plenty of examples where water has been allocated, particularly at times of higher flows, and then we find that when things returned to dry periods, there’s not enough water left over for the environment.”

A woman stands in between trees
Fiona Johnson says the research offers an opportunity to use science to avoid making mistakes. (Supplied: Fiona Johnson)

In a study published by UNSW, teams examined 63 tree rings – which contain a weather history that can date back centuries – alongside the Daly River by drilling a hole and extracting a small portion for analysis.

As trees grow they form a distinct new circle of wood around their trunk every year. Within that ring, information about age, temperature, and rainfall is recorded.

“We assume that in good conditions, in wet years, the trees will grow faster, and in dry years the trees will grow less and so the tree rings will be less thick,” Associate Professor Johnson said.

The oldest tree ring record the team could find in the Daly study was 250 years old, but by examining trees in South-East Asia, which were subject to the same monsoon climatic conditions, the scientists were able to go back further to reconstruct streamflow patterns .

Researchers examine a tree
Researchers reconstructed a rainfall period that went back almost 600 years.(Supplied: UNSW)

Government’s allocations too generous

Lead author of the study, Philippa Higgins, has taken aim at the cotton industry in particular and its plans to extract 520 gigalitres of water from the Daly River.

She said the data the government based its decisions on was too small – only dating back 50 to 60 years.

The Douglas Daly region is about 200 kilometers south of Darwin and sits on top of the Olloo Dolostone Aquifer, which has almost been fully allocated in terms of sustainable water yields for industry.

It also incorporates the Katherine Tindall Aquifer, which is also under immense pressure from over-allocations.


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