Fifteen years of regional climate downscaling in CORDEX-Australasia

Regional climate modelling plays a central role in understanding and projecting climate change across Australasia, a region characterised by complex topography, diverse climate regimes, and high exposure to climate extremes. Over the past fifteen years, CORDEX-Australasia has coordinated regional climate downscaling under an international framework while operating alongside complementary national and state-based initiatives. Here we synthesise the evolution, achievements, scientific advances, applications, and future priorities of regional climate modelling in the region. Successive CORDEX-CMIP5 and CORDEX-CMIP6 ensembles have produced the largest coordinated high-resolution projection datasets for Australasia. Regional climate models demonstrate clear added value over their driving global climate models, particularly in representing temperature extremes, heavy precipitation, coastal processes, and complex terrain. CMIP6-based projections show robust agreement on substantial 21st-century warming, with uncertainty dominated by emissions scenarios, while precipitation responses remain more regionally heterogeneous. Advances in convection-permitting modelling, benchmarking frameworks, and bias-correction methods have further improved process representation and evaluation. Regional projections now underpin applications in water resources, agriculture, disaster risk reduction, energy, health, and national climate services. Progress has been supported by shared infrastructure through the National Computational Infrastructure and strengthened coordination via the National Partnership for Climate Projections, highlighting strong synergies between State and Federal programs contributing to CORDEX. Key challenges remain including computational demands, persistent model biases, precipitation uncertainty, ensemble design, and translating complex multi-model information into decision-ready guidance. Strategic priorities include kilometre-scale (convection-permitting) modelling, enhanced Earth system coupling, coordinated super-ensembles, responsible integration of artificial intelligence approaches, strengthened observational constraints, and expanded support for vulnerable remote Australian islands and Pacific Island nations. Sustained investment, collaboration, and innovation will be essential to deliver robust, high-resolution climate information for adaptation and resilience across Australasia.