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Rainfall Variability in West Africa: The Models Fail Again
Lebel, T., Delclaux, F., Le Barbé and Polcher, J.  2000.  From GCM scales to hydrological scales: rainfall variability in West Africa.  Stochastic Environmental Research and Risk Assessment 14: 275-295.

What was done
The authors compared GCM rainfall simulations with real-world observations from West Africa for the period 1960-1990.

What was learned
The analysis revealed that the model output was affected by a number of temporal and spatial biases that led to significant differences between observed and modeled data.  GCM-simulated rainfall totals, for example, were significantly greater than what was observed, exceeding reality by 25% during the dry season and by 75% during the rainy season.  In addition, the seasonal cycle of precipitation was not well simulated; the authors noted that the model started the rainy season "too early and the increase in precipitation [was] not rapid enough."  Shortcomings were also evident in the model's inability to simulate convective rainfall events (the model simulated too much rainfall).  Furthermore, the authors note that "the interannual variability [was] seriously disturbed in the GCM as compared to what it [was] in the observations."

As for why the model performed so badly, the authors suggest two main reasons.  First, they say the parameterization of rainfall processes in the GCM is much too simple.  And the second major reason for the model's failure, according to the authors, is that the spatial resolution of the GCM is much too coarse.

What it means
This paper vividly demonstrates that, in spite of all their complexity, current general circulation models of the atmosphere are still severely lacking in their ability to accurately simulate earth's hydrologic cycle.  And if the models can't get precipitation right, how can they be expected to correctly model the planet's entire climate, of which rainfall is only one component?  In the case at hand, when the real world rains, it pours in buckets in the climate alarmists' models, falling squarely on their preposterously premature parade of unsubstantiated claims.