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Simulating 21st-Century Precipitation
Reference
O'Gorman, P.A. and Schneider, T. 2009. The physical basis for increases in precipitation extremes in simulations of 21st-century climate change. Proceedings of the National Academy of Sciences, USA 106: 14,773-14,777.

What was done
The authors, as they describe it, "assess how precipitation extremes change in simulations with 11 different climate models in the World Climate Research Program's (WCRP's) Coupled Model Intercomparison Project phase 3 (CMIP3) archive."

What was learned
Based on their findings, as well as those of others, O'Gorman and Schneider report that "in simulations with comprehensive climate models, the rate of increase in precipitation extremes varies widely among models, especially in the tropics (Kharin et al., 2007)." They also note, in this regard, that "the variations among models in the tropics indicate that simulated precipitation extremes may depend sensitively on the parameterization of unresolved and poorly understood processes [italics added]," citing the work of Wilcox and Donner (2007). In fact, they find that "climate models do not correctly reproduce the interannual variability of precipitation extremes in the tropics (Allan and Soden, 2008), or the frequency and intensity distribution of precipitation generally [italics added] (Wilcox and Donner, 2007; Dai, 2006; Sun et al., 2006)."

What it means
The two researchers say their results imply that "current climate models cannot reliably predict changes in tropical precipitation extremes," noting that "inaccurate simulation of the upward velocities may explain not only the intermodal scatter in changes in tropical precipitation extremes but also the inability of models to reproduce observed interannual variability."

References
Allan, R.P. and Soden, B.J. 2008. Atmospheric warming and the amplification of precipitation extremes. Science 321: 1481-1484.

Dai, A. 2006. Precipitation characteristics in eighteen coupled climate models. Journal of Climate 19: 4605-4630.

Kharin, W., Zwiers, F.W., Zhang, X. and Hegerl, G.C. 2007. Changes in temperature and precipitation extremes in the IPCC ensemble of global coupled model simulations. Journal of Climate 20: 1419-1444.

Sun, Y., Solomon, S., Dai, A. and Portmann, R.W. 2006. How often does it rain? Journal of Climate 19: 916-934.

Wilcox, E.M. and Donner, L.J. 2007. The frequency of extreme rain events in satellite rain-rate estimates and an atmospheric general circulation model. Journal of Climate 20: 53-69.

Reviewed 9 December 2009