Perth: Outlook 2016–17
Rainfall conditions across the Perth region are expected to improve from the 2015–16 year, which may contribute to an increase in surface water storage and aquifer recharge. Total water assets are expected to remain in surplus at 30 June 2017. Water use is expected to decrease slightly during the year, which takes into account current and anticipated climate conditions in the region.
Future prospects
This section looks forward over the next reporting period and considers what water inflows and commitments might affect the region's water resources during the 2016–17 year. Figure S20 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 S20 Water outlook for the Perth region for 2016–17
Expected inflows
At the time of publication, rainfall over the Perth region during the first nine months of the 2016–17 year (July–March) was generally above average (Figure S21) and higher than the same period last year. As a result, storage inflows were approximately four times higher (refer to the Water Corporation website), and storage volumes at 1 April 2017 were 30% full compared with 23% full at the same time last year.
Figure S21 Rainfall deciles for the Perth 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 Perth 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. These next three months, however, are usually when the least rainfall and storage inflow occurs in the region.
Given both the rainfall and the soil moisture conditions during July 2016–March 2017 have improved from the previous year (see the Bureau's Australian Landscape Water Balance product), aquifer recharge is expected to be higher than it was during the 2015–16 year.
The expected inflows for the 2016–17 year are based on the 2011–12 year, a period when similar average rainfall and soil moisture conditions were experienced. Based on these assumptions, the expected aquifer recharge from the landscape (approximately 1,400,000 ML) should exceed the expected discharge from the aquifers (approximately 880,000 ML) during the year. In addition, the combined expected precipitation (approximately 25,000 ML) and river inflows into the storages (approximately 90,000 ML) could exceed the expected evaporation from the storages (approximately 30,000 ML) during the year.
Future commitments
The expected diversions and extractions are based on water use data for the 2015–16 year; however, given the improved climate conditions expected across the region, water use is expected to decrease over the next reporting period, particularly for individual users in the agricultural sector.
Contingent water assets
The Department of Water sets extraction limits on groundwater aquifers to protect groundwater-dependent ecosystems. Only water above the prescribed minimum water table level is recognised as a water asset in the account. The volume of water that is beyond this extraction limit is considered a contingent water asset for aquifers in the region; however, similar to the recognition of groundwater assets, there is currently not enough information available regarding groundwater resources in the Perth region to allow for a volumetric estimate.