Future changes in seasonal drought in Australia

Abstract. Climate change is expected to exacerbate the frequency and intensity of drought in many water-limited regions. However, future drought changes in Australia –the driest inhabited continent on Earth– have remained stubbornly uncertain due to a lack of model agreement in projected precipitation changes in most regions. We use an ensemble of future projections from the National Hydrological Projections to assess future drought changes in Australia. The ensemble of 32 simulations was created using the Australian Landscape Water Balance model (AWRA-L) forced by four global climate models (GCMs) from the Coupled Model Intercomparison Project phase 5 that were downscaled and bias-corrected using four alternative methods. This ensemble provided an opportunity to analyse multiple sources of uncertainty on the future projections and quantify changes across multiple drought types (meteorological, hydrological and agricultural). We show future increases for all three drought types, with largest increases projected in winter and spring. The sign of the changes is consistent across different drought metrics but projected changes are more robust for the time spent under drought than drought duration or intensity. The future changes are particularly robust in the highly populated and agricultural regions of Australia, suggesting potential impacts on agricultural activities, ecosystems and urban water supply. We attributed uncertainty in future drought changes to GCMs, downscaling/bias correction (DS-BC) methods and emissions scenarios. GCMs represent the largest source of uncertainty (47 %–72 % of the full range of projections) but the choice of DS-BC method is also important (23 %–58 %, with approximately half of this uncertainty arising from the choice between dynamical and statistical downscaling). The emissions scenarios were the lowest source of uncertainty (11 %–33 %) but influenced the magnitude and spatial extent of robust future changes. Overall, the projections suggest likely future increases in drought in Australia with little evidence for ameliorating drought risk with climate change despite ongoing uncertainty in future changes in parts of the country.