South-east Queensland is a major population centre and experiences severe droughts. During the 'Millennium Drought' (2001-2009), rainfall deficit reached 1500 mm and water storages fell to c.20% capacity. Stochastic modelling suggested that while worse droughts could occur, likelihood is less than 1:10000 years.
To evaluate this expectation, we reconstructed regional rainfall over the past 7500 years. We used the carbon isotope composition of the leaves of the tree Melaleuca quinquenervia, collected monthly over eleven years, to accurately model rainfall from leaf isotope composition, and applied this to a long sequence of these leaves found preserved in lake sediments. Results accurately represented decadal-scale rainfall patterns when reconstructed and measured rainfall overlapped.
The Millennium Drought was the driest decade in 1500 years, although earlier, but less severe, dry periods lasted centuries. Thus, extended periods of rainfall deficit have occurred more frequently than 1:10000 years. Moreover, the c.120 year instrumental rainfall record is atypical of the past 1500 years. This information has great potential to inform water policy and climate change predictions in south-east Queensland.