BAMOS October 2021
16 Article
Figure 3 . Annual volume storage (%) for Burrinjuck Dam indicating rainfall or snowmelt inflows from 1913 – 2019 . Note the rapid increase in 2010 followed by a long decline from 2012 and from 2016 .
Impacts of global warming in the Murrumbidgee River catchment
The mean river height in June to September ( JJAS ) at Wagga Wagga , a city which lies upstream of water extraction for irrigation , has decreased significantly from 1965 – 1991 to 1992 – 2018 ( Fig . 1 ), as have both April – May and JJAS net inflows to Burrinjuck Dam ( Fig . 3 ) and April – May rainfall in the catchment upstream at Burrinjuck and Blowering dams .
Evaporation , particularly in the absence of rainfall or snowmelt , accentuates the lack of run-off into dams and streams because water needs to soak into dry catchments before significant run-off can occur . When large amounts of rainfall or snowmelt occur in some years in late winter / spring , for example , in a strongly negative phase of the IOD in 2016 , or in the spring / summer
La Niñas of 2010 – 12 and 2020 – 21 , major floods have occurred . This year Burrinjuck and Blowering dams received large inflows by the end of March . With very little rainfall in April or May , recent rain in June and July has resulted in the dams reaching 100 % capacity . As of writing , the river height at Wagga Wagga , after reaching 6.4 m in early August , is now 3.3 m ( mid-August ), well below the minor flood level of 7.3 m .
Without late winter / spring rainfall from a lack of favourable IOD conditions or spring / summer La Niña rainfall , continued catchment drying , and increased evapotranspiration due to warming will drastically reduce future water availability in the southern MDB owing to reduced run-off , decreased dam inflows and low river heights .
This article is a summary of a recent paper in
Scientific Reports — citation for Speer et al ( 2021 ) on the right .
References
Guest , C . 2016 . Sharing the Water : One hundred years of River Murray politics . Published by the Murray-Darling Basin Authority . MDBA publication no : 43 / 16 . ISBN ( online ): 978-1-925599-05-3
Morice , C . P ., Kennedy , J . J ., Rayner , N . A . & Jones , P . D . 2012 . Quantifying uncertainties in global and regional temperature change using an ensemble of observational estimates : the HadCRUT4 dataset . J . Geophys . Res ., 117 , D08101
http :// doi . org / 10.1029 / 2011JD017187
Risbey , J . S ., Pook , M . J ., McIntosh , P . C ., Wheeler , M . C . & Hendon , H . H . On the remote drivers of rainfall variability in Australia . Mon . Wea . Rev . 137 , 3233- 3253 ( 2009 )
https :// doi . org / 10.1175 / 2009MWR2861.1
Speer , M ., Leslie , L . M ., MacNamara , S ., Hartigan , J . 2021 . From the 1990s climate change has decreased cool season catchment precipitation reducing river heights in Australia ’ s southern Murray-Darling Basin .