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  • Boulanger, J.-P., F. Martinez and E. C. Segura, Projection of future climate change conditions using IPCC simulations, neural networksand Bayesian statistics.Part 2: Precipitation mean state and seasonal cycle in South America. Climate Dynamics. Accepted.

Projections of future climate change conditions in mean state and seasonal cycle for precipitation during the 21st century for South America are discussed. Our analysis consists of one simulation of seven Atmosphere-Ocean Global Climate Models (AOGCMs), which participated in the IPCC Project and provided at least one simulation for the 20th century (20c3m) and one simulation for each of three SRES scenarios: A2, A1B and B1. We developed a statistical method based on neural networks and Bayesian statistics to compute a transfer function between models and observations. Such a transfer function was then used to project future conditions and to derive what we would call the optimal model combination for 21st century climate change projections. To evaluate the results, various criteria were computed making it possible to evaluate the models’ skills in simulating late 20th century precipitation over continental areas as well as their divergence in projecting climate change conditions. Despite the relatively poor skill of most of the climate models in simulating present-day large scale precipitation patterns, we identified two types of models: the climate models with moderate-to-normal (i.e. close to observations) precipitation amplitudes over the Amazonian basin; and the climate models with a low precipitation in that region and too high a precipitation on the equatorial Pacific coast. Under SRES A2 greenhouse gas forcing, the neural network simulates an increase in precipitation over the La Plata basin coherent the mean model ensemble projection. Over the Amazonian basin, a decrease in precipitation is projected. However, the models strongly diverge, and the neural network was found to give more weight to models, which better simulate present-day climate conditions. In the southern tip of the continent, the models poorly simulate present-day climate. However, they display a fairly good convergence when simulating climate change response with a weak increase south of 45°S and a decrease in Chile between 30°S and 45°S. Other scenarios (A1B and B1) strongly resemble the SRES A2 trends but with weaker amplitudes.

Last Updated: 2006-03-29

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