A review of historic and future hydrological changes in the Murray-Darling Basin

The Murray-Darling Basin is Australia's food bowl and home to many iconic water bodies that are culturally and ecologically highly valued. The recent Millennium Drought (from mid-1990s to 2009) was the most severe hydrological drought since records started in the late 19th century. It severely impacted on the basin and for many acted as a wake-up call. To address the ongoing declines in water resources and environmental conditions and to prepare the region for climate change, Australia's Governments are currently attempting to introduce a new comprehensive, and integrated approach to the management of the basin's water resources. In this paper, long-term time series of climate, hydrological and environmental data are used to analyze how compounding stresses have gradually affected the hydrological system and its services. Major hydroclimatic stresses considered in this paper include salinity, water use, droughts, and climate change. Other, more localized or minor stresses exist (groundwater extraction, farm dams, afforestation, bush fires, cyanobacterial blooms and pollutants) and are reviewed more briefly. The history of water policy and planning shows that Government actions have been strongly influential on the basin. A shift in the strategic goals from water development to the protection and restoration of environmental assets is noticeable since the mid 1990s. Median climate change projections by 2030 indicate smaller reductions in rainfall and runoff than those observed during the recent Millennium Drought, but have a relatively high uncertainty attached to them. The use of regional approaches to reduce that uncertainty, such as statistical downscaling, points to a sizeable decline in rainfall by the end of the century. Most climate projections used for planning consider greenhouse emission scenarios that have smaller global emission trends than the one observed over the last decade. Other, 'less optimistic' scenarios have to be considered for long-term water planning and food security. Compounding all these stresses, is the naturally high hydroclimatic variability of this semi-arid region, that may have been insufficiently considered during previous water development and planning efforts. Successful water planning will need to balance cultural and ecological values with food production, account for high natural variability and uncertainty in climate change projections, learn from past mistakes and be cognizant of future hydrological changes