BAMOS October 2021
14 Article
Impact of climate change on the waters of the Murray-Darling Basin
Milton Speer , Lance Leslie , Shev MacNamara and Joshua Hartigan
Murrumbidgee River dry river-bed at Hay , NSW in the 1990s . Image supplied by authors .
River heights have dropped in the southern Murray-Darling Basin , particularly since the 1990s .
The Murray-Darling Basin ( MDB ) is Australia ’ s major agricultural region , producing almost 40 % of the national food supply during the growing season ( April – September ) ( Holland et al . 2015 ). In comparison , the agricultural area of the central valley of California provides approximately 20 % of the total US food production ( USGS ).
The extended drought conditions since the mid – 1990s in the MDB , comprising the Millennium Drought ( 1997 – 2009 ) ( Bureau of Meteorology 2019 ; Post et al . 2014 ) and the 2017 – 2019 drought , have resulted in rivers running dry and low water storages , affecting communities , businesses , animals , and the environment .
The southern MDB , which occupies the southern half of New South Wales and northern Victoria , receives most of its annual catchment run-off during the cool or growing season ( April- September ). Global warming has accelerated in the latter half of last century ( IPCC 2014 ; Morice et al . 2012 ) and particularly since the 1990s in Australia ( Bureau of Meteorology 2020 ). As a result , new research ( Speer et al . 2021 ) shows that April – May cool season rainfall , net inflows to the main dams of Burrinjuck and Blowering in the upper part of the catchment and downstream river heights have significantly decreased in the Murrumbidgee River catchment in the southern MDB . In effect , the amount of water flowing past Wagga Wagga has decreased by approximately 30 % since the 1990s . This is not likely a result of irrigation in the region as more than 80 % of irrigation for agriculture occurs downstream of Wagga Wagga .
Effect of river regulation
There has been no new regulatory infrastructure on the Murrumbidgee River after Blowering Dam was completed during the 1960s . Even after Burrinjuck Dam was completed in 1928 , the Murrumbidgee River used to regularly spill over the banks ( minor flood level ) at both Wagga Wagga ( Fig . 1 ) and Hay ( Fig . 2 ) further downstream during the cool season ( April – September ) until the early 1990s .
Drying trends
There have been downward trends in rainfall since the 1990s in southern parts of eastern Australia , and in the higher rainfall areas of the MDB catchments that generally are located in the highlands of the Great Dividing Range ( Murphy and Timbal 2008 ). These trends are concentrated in the cooler half of the year , from April to September ( Bureau of Meteorology 2019 ). A major influence on this drying trend has been the