Projected precipitation extremes from CMIP6 and CORDEX-CMIP6 downscaled simulations in Australian capital cities

Australian urban population accounts for over 90% of total population and is concentrated in coastal areas. Projections show that the extreme precipitatio will be more intense and frequent. We investigated changes to daily mean, moderately extreme (99^th and 99.7^th percentile), and rare extreme (Annual Exceedance Probability (AEP) 1 in 10, 50, and 100) precipitation events in Australia and within its greater capital cities. We used downscaled daily precipitation data from CMIP6 models and downscaled CORDEX-CMIP6 precipitation simulations for SSP370 completed by four modelling groups in Australia (Grosse et al., 2023). This ensemble consists of 19 different host CMIP6 models and ensemble of 39 different downscaled simulations. The changes were quantified according to the rate of change per degree of global warming. The largest increases to precipitation extremes were seen over northern Australia, with the AEP 1-in-50 event in Darwin projected to increase by 11.2%/K or 13.3%/K for the CMIP6 host models and downscaled ensembles, respectively. Projected changes from the downscaled ensemble were lower though still substantial in other capital cities (7.7%/K for Brisbane, 7.1%/K for Sydney, 4%/K for Melbourne, and 5.3%/K for Perth). Large spatial differences were noted among the downscaled ensembles, with 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 can be accounted for. Presentation will also show selected results for sub-hourly analysis of rainfall changes for selected stations in Australia from using 15 member ensemble of UQ-DES CCAM downscaled simulations.

Grose, M. et al., 2023. A CMIP6-based multi-model downscaling ensemble to underpin climate change services in Australia. Climate Services, 30, p.100368.