Abstract
Abstract. Using the general circulation model ECHAM5–JSBACH forced by observed sea surface temperatures (SSTs) for the 20th century, we investigate the role of vegetation and land surface albedo dynamics in shaping rainfall variability in the Sahel. We use two different land surface albedo schemes, one in which the albedo of the canopy is varying and one in which the albedo changes of the surface below the canopy are also taken into account. The SST forcing provides the background for simulating the observed decadal signal in Sahelian rainfall, though the response to SST forcing only is not strong enough to fully capture the observed signal. The introduction of dynamic vegetation leads to an increase in interannual variability of the rainfall, and gives rise to an increased number of high-amplitude rainfall anomaly events. The dynamic background albedo leads to an increased persistence of the rainfall anomalies. The increase in persistence means that the difference between the dry and the wet decades is increased compared to the other simulations, and thus more closely matching the observed absolute change between these two periods. These results highlight the need for a consistent representation of land surface albedo dynamics for capturing the full extent of rainfall anomalies in the Sahel.
Highlights
Climate variability is important for vegetation distribution and vegetation variability, especially in deserts and semideserts, where the vegetation response depends on changes in the mean climate and on changes in patterns of variability, such as extreme events and the temporal structure of the change (Ni et al, 2006)
Adding the dynamic vegetation (VEGDYN + BGSTAT) does not affect the long-term mean rainfall much, and the simulated rainfall amount of this setup is lower than the observed precipitation (Fig. 3a)
Using a general circulation model coupled to a land surface model (ECHAM5–JSBACH) we investigate the role of vegetation and land surface albedo dynamics in shaping rainfall variability in the Sahel
Summary
Climate variability is important for vegetation distribution and vegetation variability, especially in deserts and semideserts, where the vegetation response depends on changes in the mean climate and on changes in patterns of variability, such as extreme events and the temporal structure of the change (Ni et al, 2006). The focus of this paper is on the land surface processes involved in the coupling between vegetation variability and precipitation variability in the Sahel as simulated for the 20th century. During the 20th century, the region saw a long wet period followed by an extended drought, which peaked in the early 1980s. Characteristic for these periods were their persistence and severity. A large amount of research have been devoted to the processes responsible for these variations, especially the causes for the extended drought period. It is generally accepted that changes in the SST patterns provide the background variability for decadal variability in Sahelian precipitation (Giannini et al, 2003; IPCC, 2007), though there is still some debate
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