Autumn precipitation trends over Southern Hemisphere midlatitudes as simulated by CMIP5 models (6620)
In recent decades, Southern Hemisphere midlatitude regions such as southern Africa, southeastern Australia and southern Chile have experienced a reduction in austral autumn precipitation; the cause of which is poorly understood. This study focuses on the ability of climate models that form part of the Coupled Model Intercomparison Project phase 5 to simulate these trends, their relationship with extratropical and subtropical processes, and implications for future precipitation changes. Models underestimate both the historical autumn poleward expansion of the subtropical dry zone and the positive Southern Annular Mode (SAM) trend. The multi-model ensemble (MME) is also unable to capture the spatial pattern of observed precipitation trends across semi-arid midlatitude regions. However, in temperate regions that are located further poleward such as southern Chile, the MME simulates observed precipitation declines. The MME shows a strong consensus in twenty-first century declines in autumn precipitation across southern Chile in both the medium-low and high Representative Concentration Pathway (RCP) scenarios, and across southern Africa in the high RCP scenario, but little change across southeastern Australia. Projecting a strong positive SAM trend and continued subtropical dry-zone expansion, the models converge on large SAM and dry-zone expansion-induced precipitation declines across southern midlatitudes. In these regions, the strength of future precipitation trends is proportional to the strength of modelled trends in these phenomena, suggesting that unabated greenhouse gas-induced climate change will have a large impact on austral autumn precipitation in such midlatitude regions.