Melbourne: Outlook 2016–17
Average rainfall is expected across the Melbourne region, and should contribute to an increase in surface water storage. Total region water use is expected to increase during the year, taking into account expected climate conditions and demands. Total water assets are expected to remain in surplus at 30 June 2017.
Future prospects
This section looks forward 12 months and considers what water inflows and commitments might affect the region's water resources during the 2016–17 year. Figure S15 shows that there is a surplus of available water assets and future water rights over water liabilities and future water commitments that are expected to be settled within 12 months of the reporting date.
Figure S15 Water outlook for the Melbourne region for 2016–17
Expected inflows
At the time of publication, rainfall over the Melbourne region during the first nine months of the 2016–17 year (July–March) was generally average (Figure S16).
Figure S16 Rainfall deciles for the Melbourne region from July 2016–March 2017
The Bureau's climate outlook (released on 30 March 2017) indicates a high probability of below-average rainfall over most of southern Australia, including the Melbourne region, for the next three months (April–June 2017). This outlook is influenced by warming of tropical Pacific sea surface temperatures and a cooler than average eastern Indian Ocean. Therefore, given the current relatively wet soil moisture conditions in March 2017 (see the Bureau's Australian Landscape Water Balance product) attributed to the past rainfall which occurred in the region, annual streamflows and storage inflows are expected to be average during the 2016–17 year.
The expected net inflows for the 2016–17 year are estimated based on the 2012–13 year, a period when similar average rainfall and soil moisture conditions were experienced (Figure S15). Based on these assumptions, the combined expected precipitation (approximately 40,000 ML) and river inflows into the storages (approximately 490,000 ML) could well exceed the expected evaporation from the storages (approximately 50,000 ML) during the year.
The expected inter-region supply during the 2016–17 year of 200,000 ML is estimated based on last year's delivered volume. The Victorian Desalination Plant at Wonthaggi is also expected to provide 50,000 ML of desalinated water during the year.
Future commitments
The expected diversions and extractions are based on water use data for the 2015–16 year; however, based on recent trends, water use is expected to increase by 0–5%.
Contingent water assets and contingent water liabilities
Contingent water assets
Sustainable yields have been estimated for all groundwater resources within Victoria, in the context of the permissible consumptive volumes (PCV). These were determined by the Victorian Department of Environment, Land, Water and Planning and represent the long-term average annual volume permitted to be extracted from aquifers within the Melbourne region. The limits are set to ensure groundwater is maintained at a sustainable level and are sufficient to maintain groundwater dependent ecosystems within the region.
The methods used to determine sustainable yields varied across Victoria according to the characteristics of the aquifers being investigated, and in many cases the full volume of the aquifer could not be accurately quantified.
Water resource managers within the Melbourne region must adhere to the PCV extraction limitations for groundwater resources in the Melbourne region. The combined volume of the PCV has been recognised as a water asset in the National Water Account 2016. The volume of water that is beyond this extraction limit is considered a contingent water asset in the Melbourne region; however, there is currently not enough information available regarding the aquifers in the region to allow for a volumetric estimate.
Contingent water liabilities
There are no contingent water liabilities in the Melbourne region.