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The rivers of the south-eastern Murray-Darling Basin (MDB) and the associated irrigation areas of the southern riverine plain (SRP) in south-eastern Australia have undergone major hydrological changes over the last 30 years. These include a period of lower rainfall; a rebalance of surface water diversions between consumptive and environmental water uses under the MDB Basin Plan, improvements in water infrastructure; water trade out of the region; and falling groundwater levels. All these changes increase losses from streams to groundwater systems; potentially leading to the need for greater releases from dams to maintain baseflow in the major rivers. Baseflow is important for conveyance of water, water quality and baseflow-dependent ecosystems during dry periods. Hydrological changes in the SRP will reduce the streamflow by 2029–30 by an estimated 80 to 320 GL/yr. Further hydrological changes by 2029–30 will reduce the streamflow by another 50 GL/yr in the following decade. This is the first assessment of the cumulative stream impacts of the SRP and is relatively lower than previous assessments for single drivers. The current approach of mitigating unexpected losses is to increase conveyance loss budgets as required. This could be extended to mitigate the lower end of potential impacts; but further steps to reduce losses may be required towards the upper end. Further actions include a review of extraction limits for surface water and groundwater, trigger levels, and a greater shift towards conjunctive water management. Groundwater extraction, which has dominated impacts, is increasing from a relatively low proportion of the extraction limit in Goulburn-Murray Sedimentary Plain and shallow aquifers of the SRP. Over time, climate change will become more dominant as a driver. Most monitoring required to support mitigation already exists, but data is not collated or reported in a form relevant for stream impacts. Modelling also needs to be updated with reporting of more relevant outputs. [ABSTRACT FROM AUTHOR]

Restoration programmes for degraded aquatic ecosystems frequently focus on flow restoration or reinstatement, including recovery targets for volumes of water to be used for environmental benefit. Australia's Murray–Darling Basin is an example of a major system undergoing substantial water reform to balance the needs of competing users, including the environment, within the constraints of an arid climate. This reform revolves around accounting for finite volumes of water that have been shared amongst water users. We argue that while recovering water will provide good outcomes, as a sole intervention, it is not enough to deliver the desired environmental benefits of the reform given the significantly altered state of the catchment. Here, we present 10 measures that could be used to complement planned water recovery actions. These "complementary measures" integrate recovery actions, which when strategically combined with water delivery would significantly enhance water reform efforts to generate environmental outcomes in a highly modified system. [ABSTRACT FROM AUTHOR]

• The influence of management decisions on water allocations are often overlooked. • Effects of different water management rules were simulated in two Australian rivers. • Changing management rules alone varied long-term water allocations by −6 to +22%. • Influence of drivers varied with river system and reliability of water license. • More systematic and transparent water allocation decisions will be beneficial. A global challenge for water resource management in rivers worldwide is ensuring water supply reliability satisfies consumptive and environmental demands. High variability in water supply, water policy and management decisions, and uncertainty about the effects of climate change compound this challenge. Understanding factors driving water allocations and consequences for water users and the environment is essential. Rainfall and streamflow traditionally drive allocations, yet the influence of water management decisions are often overlooked because they are complex, rarely codified and dependent on the regional context. We compared the relative influences of water management, climate and the river system characteristics including demand and water storage infrastructure on regulated and unregulated water allocations in two regulated rivers with large dams for water supply to towns, irrigated agriculture and wetlands of international significance (Gwydir and Macquarie Rivers of the Murray-Darling Basin, southeastern Australia), using hydrological simulation models and regression-based sensitivity analyses under an historical and drier climate. Water management decisions influenced regulated water allocations (explaining 23% to 52% of the variance) considerably more than unregulated water allocations (explaining 2%). For regulated water allocations, water management decisions and the river system were more important than a plausible change in climate, while for unregulated water allocations, the river system and climate change were dominant drivers. Changing management rules alone could vary long term water allocations by between −6% and +0.1% in the Gwydir River and between −4% and +22% in the Macquarie River. Management rules which allocated future inflows (i.e. credit model) were more likely to fail in a drying environment with projected reductions in runoff, compared to rules where only water in storage is allocated (i.e. debit model). Management rules differed despite both river systems being governed by a single management agency under the same legislative and policy framework. More systematic approaches to justify water management rules and greater transparency in their influence on water allocations are critical for maximizing the benefits to water users and river health, and for managing risks to water supply in a variable and changing climate. [ABSTRACT FROM AUTHOR]

Climate change is threatening water security in water-scarce regions across the world, challenging water management policy in terms of how best to adapt. Transformative new approaches have been proposed, but management policies remain largely the same in many instances, and there are claims that good current management practice is well adapted. This paper takes the case of the Murray–Darling Basin, Australia, where management policies are highly sophisticated and have been through a recent transformation in order to critically review how well adapted the basin's management is to climate change. This paper synthesizes published data, recent literature, and water plans in order to evaluate the outcomes of water management policy. It identifies several limitations and inequities that could emerge in the context of climate change and, through synthesis of the broader climate adaptation literature, proposes solutions that can be implemented when basin management is formally reviewed in 2026. [ABSTRACT FROM AUTHOR]

Practitioners of environmental water management (EWM) operate within complex social-ecological systems. We sought to better understand this complexity by investigating the management of environmental water for vegetation outcomes. We conducted an online survey to determine practitioners' perspectives on EWM for non-woody vegetation (NWV) in the Murray-Darling Basin, Australia with regards to: i) desirable outcomes and benefits; ii) influencing factors and risks; iii) challenges of monitoring and evaluation, and iv) improving outcomes. Survey participants indicated that EWM aims to achieve outcomes by improving or maintaining vegetation attributes and the functions and values these provide. Our study reveals that EWM practitioners perceive NWV management in a holistic and highly interconnected way. Numerous influencing factors as well as risks and challenges to achieving outcomes were identified by participants, including many unrelated to water. Survey responses highlighted six areas to improve EWM for NWV outcomes: (1) flow regimes, (2) vegetation attributes, (3) non-flow drivers, (4) management-governance considerations, (5) functions and values, and (6) monitoring, evaluation and research. These suggest a need for more than 'just water' when it comes to the restoration and management of NWV. Our findings indicate more integrated land-water governance and management is urgently required to address the impacts of non-flow drivers such as pest species, land-use change and climate change. The results also indicate that inherent complexity in EWM for ecological outcomes has been poorly addressed, with a need to tackle social-ecological constraints to improve EWM outcomes. [Display omitted] • Flow is important for vegetation, but management requires more than just water. • Integrated land-water management is needed to limit impacts of non-flow drivers. • Constraints need to be addressed to improve vegetation outcomes to flow regimes. • Practitioners perceive vegetation management in holistic and interconnected ways. • Building societal understanding of environmental water management is important. [ABSTRACT FROM AUTHOR]