Murray River flow down 40pc as climate change bites, MDBA says

MDBA data show average water flows in the Murray River were two-fifths less during the 21st Century than the average from 1904 to 2000.

Using modelling that assumed historical weather conditions and no water extraction, the MDBA calculated that water moving through Australia's food bowl has been 40 per cent less in the past 20 years than for the previous century.

Part of the problem is changing weather patterns, which are producing less winter rainfall in south-eastern Australia. Another problem is how hotter weather impacts the land in river catchments.

In a discussion paper on climate change and the Murray Darling Basin plan, published in February, the MDBA said the impacts on water resources "are wide ranging and significant".

Higher temperatures increase evaporation and reduce soil moisture - which means less run-off when it rains.

That's doubly bad for crops and native fauna, which will lose more moisture to transpiration and need more rainfall or irrigation to make up for poor soil moisture.

A graph showing the MDBA Murray River flow modelling was published in an article last week (and authored by ABARES senior economist Neal Hughes).

The chart shows modelled flow data for the Murray River, assuming historical weather conditions and no water extraction, over the past century. It shows that average water flows this century are about 40 per cent below the average of the 20th century.

"The chart underlines how rainfall and inflows into the Murray system have been well below the historical average since 2000, and demonstrate the importance of using data going back for more than a century to understand the potential impacts of climate variability," the MDBA said in a statement to this publication.

"In addition this analysis highlights the importance of considering longer-term trends that may be associated with climate change."

ABARES ' Mr Hughes argued that low rainfall was the dominant factor driving up water prices, much more so than foreign investors, corporate speculators, state government water-sharing rules, new almond plantings and water recovery under the Murray-Darling Basin Plan.

"We know these reductions are at least partly related to climate change, driven by both reduced winter rainfall and higher temperatures," he said.

"Lower rainfall and higher temperatures also make crops thirstier, increasing demand for irrigation water. This was evident in January, when temperatures exceeded 35 for 14 days and irrigators' demand for water spiked from about 4.5 gigalitres to 7GL a day."