Substantial increases in future precipitation extremes – insights from a large ensemble of downscaled CMIP6 models

Extreme precipitation events are widely held to become more intense and frequent as a result of climate change, which will have major impacts for future flooding with implications for the environment, infrastructure, agriculture, and human life. We investigated projected changes to daily mean, moderately extreme (99th and 99.7th percentile), and rare extreme (Annual Exceedance Probability (AEP) 1 in 10, 50, and 100) precipitation events across Australia and its greater capital cities, where approximately two thirds of the Australian population reside. We used dynamically downscaled CMIP6 precipitation simulations from 4 modelling groups in Australia. This large ensemble consists of 19 different host models downscaled using 3 distinct regional climate models in 5 different configurations, making an ensemble of 39 different downscaled simulations. The changes in mean and extreme precipitation events were quantified at each grid cell from each of the models according to the rate of change per degree of global warming. The largest increases to precipitation extremes were seen over northern Australia, with the 1 in 100 AEP event in Darwin projected to increase by 11.9% K ^− 1 and 12.2% K ^− 1 for the downscaled and host ensemble averages, respectively. Other capital cities had lower increases but still substantial (7.6% K ^− 1 for Brisbane, 7.3% K ^− 1 for Sydney, 3.4% K ^− 1 for Melbourne, and 4.4% K ^− 1 for Perth). Large spatial differences were noted among the downscaled ensembles, with models from different modelling groups showing varying spatial patterns and magnitudes of change. These results highlight the influence of the downscaling approach in determining changes to precipitation extremes and show the need to consider large ensembles to ensure uncertainties in host models and downscaling methods can be accounted for. The findings can inform decision making around flood management, urban planning, urban water supply and agriculture around Australia, in addition to revealing globally relevant scientific insights.