Human activity has modified the environment at all scales from the smallest ecosystems to the global climate systems. In the analysis of the Murray-Darling Basin, it is necessary to take account of effects of human activity ranging from local changes in water tables and soil structure through basin-level effects of the expansion of irrigation to changes in precipitation pattern arising from the accumulation of greenhouse gases in the atmosphere. In this paper, we analyse the impact of, and adjustments to, climate change in the Murray-Darling Basin, using a simulation model that incorporates a state-contingent representation of uncertainty.