KEY WORDS: Biosphere-atmosphere interactions Climate transition Drought Ecosystem dynamics Multiple climate equilibria West Africa

This paper presents both theoretical and numerical analyses on the multiple-equilibrium nature of the regional climate system in West Africa. Based on simple analyses on how the coupled biosphere-atmosphere system responds to vegetation perturbations within the scope of a dynamic ecosystem, we propose that the regional climate system may have multiple equilibrium states coexisting under the same precessional forcing. Using a synchronously coupled biosphere-atmosphere model which includes explicit representation of ecosystem dynamics, we show that the equilibrium state of the model is sensitive to initial vegetation distribution. This modelling result supports the existence of multiple climate equilibria. Using the same model, further experiments are canied out to investigate how the coupled system responds to non-permanent vegetation perturbations. Our results demonstrate how transitions between different climate equilibria can take place when governed by the two-way biosphere-atmosphere feedback. These findings advance our understanding regarding the mechanisms of climate variability over West Africa