The application of river-system models to inform water-resource planning and management is a growing global phenomenon. This requires models to be applied so that they are useful to water decision makers charged with setting targets that provide adequate water flows to sustain landholders and communities. This article examines why and how the innovative application of river-system models can facilitate interactions between water science and water management in Australia’s Murray–Darling Basin (the Basin). A trajectory river-modelling method was applied to run multiple short historical climate sequences through a river-system model to provide historical probabilities. These can allow better assessment of the risks and impacts associated with stream flow and water availability. This method allows known historical variability to be presented, and produces relevant results for a 10–15-year water-sharing plan lifetime. The benefits were demonstrated in the Basin’s Lachlan Catchment where modelled river-flow results demonstrated the increased variability between shorter 15-year sequences than for a single 114-year run. This approach highlighted the benefits of expressing modelling results as historical probabilities to inform short-term and strategic water-planning efforts.