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The Sad State of Sub-Daily Precipitation in CMIP5 Climate Models
Rosa, D. and Collins, W.D. 2013. A case study of subdaily simulated and observed continental convective precipitation: CMIP5 and multiscale global climate models comparison. Geophysical Research Letters 40: 10.1002/2013GL057987.

The authors write that the occurrence of extreme rainfall that causes floods and landslides "is under-estimated in Global Climate Models (GCMs)," citing Stephens et al. (2010); and they say that "this bias can affect decisions at both the individual and the community level," which makes the current state of affairs a sad state of affairs.

What was done
Hoping to chart a course that could lead to our extricating ourselves from this undesirable situation, and noting that heavy rainfall is mainly due to cloud cumulus convection (CC), Rosa and Collins investigated which approaches best estimate the observed frequency distribution of heavy rainfall by analyzing data from the archives of conventional GCMs that have different CC parameterizations and that were part of the Coupled Model Intercomparison Project Phase 5 (CMIP5), as well as the results of a multi-scale GCM "which resolves cloud processes explicitly and has been shown to compare better to observations (Li et al., 2012)."

What was learned
The two researchers report that the CMIP5 GCMs (1) "react too quickly to local convective instability" and, therefore, that they (2) "overestimate the incidence of middle rainfall events," and that they (3) "underestimate the incidence of no, little, and heavy rainfall events," while they (4) "overestimate the persistence of heavy precipitation" and (5) "underestimate the persistence of no and light precipitation," while also noting that (6) "the multiscale GCM has the best estimate of the diurnal cycle and a good estimate of heavy rainfall persistence."

What it means
It would appear that the vast majority (all but one?) of the "latest and greatest" of the world's host of GCMs - the CMIP5 group - still fall short of what is desired of them in the area of modelling precipitation.

Li, F., Rosa, D., Collins, W.D. and Wehner, M.F. 2012. "Super-parameterization": A better way to simulate regional extreme precipitation? Journal of Advances in Modeling Earth Systems 4: 10,1029/2011MS000106.

Stephens, G.L., L'Ecuyer, T., Forbes, R., Gettlemen, A., Golaz, J.-C., Bodas-Salcedo, A., Suzuki, K., Gabriel, P. and Haynes, J. 2010. Dreary state of precipitation in global models. Journal of Geophysical Research 115: 10.1929/2010JD014532.

Reviewed 19 March 2014