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Autumn Precipitation Trends in Southern Hemisphere Midlatitudes
Purich, A., Cowan, T., Min, S.-K. and Cai, W. 2013. Autumn precipitation trends over Southern Hemisphere midlatitudes as simulated by CMIP5 models. Journal of Climate 26: 8341-8356.

The authors write that "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."

What was done
Hoping to get a better understanding of this set of real-world circumstances, and "with the recent availability of the next generation of global climate models from phase 5 of the Coupled Model Intercomparison Project (CMIP5)," in the words of Purich et al., they decided to "assess the ability of these models to capture the observed trends in austral autumn precipitation across the Southern Hemisphere midlatitude regions," so as to be able to determine "implications for future precipitation changes."

What was learned
The four researchers report, unfortunately, that "on the whole, CMIP5 models are unable to capture many of the observed trends in precipitation during autumn, notably failing to simulate observed declines in southern Africa and southeastern Australia." And they also state that "the positive trend in the multi-model ensemble (MME) Southern Annular Mode (SAM) index is only about half the strength of that observed."

What it means
The concluding message of Purich et al.'s investigation, as they phrase it, is that "to assist in reducing the uncertainty in future precipitation projections, further work investigating the limited ability of climate models in simulating observed historical trends in precipitation over many Southern Hemisphere regions is required [italics added for emphasis]." And as this statement clearly indicates, the world's climate-model-builders still have a long way to go before they get to where they need to be, in order to have much confidence about what the newer models they will ultimately create will be able to do, which - it is hoped - will be (in this case) to accurately predict the future nature of Southern Hemisphere midlatitude precipitation.

Reviewed 2 April 2014