Rainfall in Victoria has been decreasing since the 1970s, particularly in winter and spring – the main seasons when rainfall replenishes rivers, reservoirs and groundwater.
This drop in rainfall is likely to get worse. Climate projections show that over time Victoria’s climate will become warmer and drier, reducing the flow and amount of water in our rivers.
By 2030, stream flow is projected to decrease by 25 to 40 percent in river systems in northern and western Victoria.
By 2070, stream flow may decrease by up to 50 percent across much of the state.
A rise in temperature of just one degree Celsius in the Murray-Darling Basin would reduce annual inflow by 15 percent even if rainfall doesn’t change.
Recent research suggests that prolonged drought may influence how catchments function, reducing run-off even more than the climate models predict. Coupled with the recent record temperatures, this new research suggests that the impacts of climate change may be much greater than even the worst-case modelled scenarios.
The situation is made worse for rivers and wetlands by the way water is shared between people and the environment. In most river systems there is a cap on the amount of water that can be diverted for use, and any water that is left over after that (‘above cap’ water) is for environmental purposes. When inflows are reduced by drought or climate change, above cap water – the environment’s share – is impacted the most. Users may have to cope with less water through restrictions or reduced allocations, but the environment is impacted even more heavily and in some rivers may lose its share altogether.
 Commissioner for Environmental Sustainability Victoria, 2008, State of the Environment Report, p. 421
 DSE, 2009, Northern Region Sustainable Water Strategy p.24