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Problems with CMIP5 Models Predicting South African Rainfall

Paper Reviewed
Dieppois, B., Rouault, M. and New, M. 2015. The impact of ENSO on Southern African rainfall in CMIP5 ocean atmosphere coupled climate models. Climate Dynamics 45: 2425-2442.

Introducing their work, Dieppois et al. (2015) describe how they studied "the ability of 24 ocean-atmosphere global coupled models from the Coupled Model Intercomparison Project 5 (CMIP5) to reproduce the teleconnections between El Niño Southern Oscillation (ENSO) and Southern African rainfall in austral summer using historical forced simulations, with a focus on the atmospheric dynamic associated with El Niño." And what did they thereby discover?

Not surprisingly, the three Republic of South Africa researchers report that (1) "overestimations of summer rainfall occur over Southern Africa in all CMIP5 models," that (2) "abnormal westward extensions of ENSO patterns are a common feature of all CMIP5 models," that (3) "the warming of the Indian Ocean that happens during El Niño is not correctly reproduced," and that (4) "from the near-surface to mid-troposphere, CMIP5 models underestimate the observed anomalous pattern of pressure occurring over Southern Africa that leads to dry conditions during El Niño years."

As for what progress may or may not have been achieved by today's CMIP5 models, therefore, Dieppois et al. write that "numerous weaknesses in simulating ENSO spatiotemporal variability are still present in most CMIP5 models and do not differ much from CMIP3 experiments," citing in this regard the findings of AchutaRao and Sperber (2006), Capotondi et al. (2006), Lin (2007) and Bellenger et al. (2013), all of which facts are indicative of the unfortunate phenomenon of "going nowhere fast."

AchuataRao, K. and Sperber, K.R. 2006. ENSO simulation in coupled ocean-atmosphere models: are the current models better? Climate Dynamics 27: 1-15.

Bellenger, H., Guilyardi, E., Leloup, J., Lengaigne, M. and Vialard, J. 2013. ENSO representation in climate models: from CMIP3 to CMIP5. Climate Dynamics 42: 1999-2018.

Capotondi, A., Wittenberg, A. and Masina, S. 2006. Spatial and temporal structure of tropical pacific interannual variability in 20th century coupled simulations. Ocean Models 15: 274-298.

Lin, J.-L. 2007. The double-ITCZ problem in IPCC AR4 coupled GCMs: ocean-atmosphere feedback analysis. Journal of Climate 20: 4497-4525.

Posted 17 March 2016