Rainfall across the central region can vary from the eastern to the western systems. In 2020-21, the Yarra and Tarago systems had above-average rainfall. Natural events met many planned environmental watering actions in both of these systems in 2020-21, and strong allocations of water for the environment and carryover will enable a large proportion of potential watering actions to be delivered in 2021-22. The other systems in the central region had average or above-average rainfall in 2020-21, but inflows to system storages were variable. Low inflows to Rosslynne Reservoir meant there was no opportunity for the VEWH to purchase water for environmental use in the Maribyrnong system.
In the Werribee system, Pykes Creek and Melton reservoirs filled and spilled, but Merrimu Reservoir remained below 50 percent capacity throughout 2020-21. Lal Lal Reservoir filled and spilled in spring 2020-21, which provided important flow and allocations of water for the environment in the Moorabool system. Upper Barwon Reservoir only reached 70 percent capacity in 2020-21, but it was sufficient to deliver the full allocation of water for the environment for the year in the Barwon River.
The Bureau of Meteorology has forecast slightly above-average rainfall across the central region in autumn and winter 2021, but La Niña conditions have weakened, which may lead to drier conditions later in 2021-22. Large carryover volumes and secure water allocations will allow a wide range of watering actions to be delivered in the Yarra, Tarago and Werribee systems under all climate scenarios, to build on 2020-21 outcomes to improve environmental condition and ecosystem resilience. In contrast, the Maribyrnong system remains relatively dry, and Rosslynne Reservoir will need significant inflows during winter and spring 2021 to create an opportunity to purchase and use water for environmental flows. Environmental watering options in the Moorabool and Barwon systems in 2021-22 will be more heavily influenced by local climatic conditions than the Melbourne Water systems, due to their smaller and more variable environmental allocations. Larger flows to improve environmental condition will only be delivered in Moorabool Yulluk (Moorabool
River) and the upper Barwon River under average and wet climate scenarios. Flows will be delivered at the lower end of their recommended range in Moorabool Yulluk (Moorabool River) and the upper Barwon River under drought and dry climate scenarios, to maintain refuge habitats and limit any decline in environmental condition. Environmental watering in the lower Barwon wetlands is not affected by annual allocations of water for the environment, and the proposed fill in winter/spring and partial draw down in summer/autumn should be possible under all climate scenarios.