Abstract
Abstract. Africa has been undergoing significant changes in climate and vegetation in recent decades, and continued changes may be expected over this century. Vegetation cover and composition impose important influences on the regional climate in Africa. Climate-driven changes in vegetation structure and the distribution of forests versus savannah and grassland may feed back to climate via shifts in the surface energy balance, hydrological cycle and resultant effects on surface pressure and larger-scale atmospheric circulation. We used a regional Earth system model incorporating interactive vegetation–atmosphere coupling to investigate the potential role of vegetation-mediated biophysical feedbacks on climate dynamics in Africa in an RCP8.5-based future climate scenario. The model was applied at high resolution (0.44 × 0.44°) for the CORDEX-Africa domain with boundary conditions from the CanESM2 general circulation model. We found that increased tree cover and leaf-area index (LAI) associated with a CO2 and climate-driven increase in net primary productivity, particularly over subtropical savannah areas, not only imposed important local effect on the regional climate by altering surface energy fluxes but also resulted in remote effects over central Africa by modulating the land–ocean temperature contrast, Atlantic Walker circulation and moisture inflow feeding the central African tropical rainforest region with precipitation. The vegetation-mediated feedbacks were in general negative with respect to temperature, dampening the warming trend simulated in the absence of feedbacks, and positive with respect to precipitation, enhancing rainfall reduction over the rainforest areas. Our results highlight the importance of accounting for vegetation–atmosphere interactions in climate projections for tropical and subtropical Africa.
Highlights
The Sahel greening and Congo rainforest browning observed since the 1980s suggest that Africa has been undergoing significant changes in the structure, composition and distribution of vegetation during recent decades (Eklundh and Olsson, 2003; Olsson et al, 2005; Jamali et al, 2014; Zhou et al., 2014)
We found that increased tree cover and leafarea index (LAI) associated with a CO2 and climate-driven increase in net primary productivity, over subtropical savannah areas, imposed important local effect on the regional climate by altering surface energy fluxes and resulted in remote effects over central Africa by modulating the land–ocean temperature contrast, Atlantic Walker circulation and moisture inflow feeding the central African tropical rainforest region with precipitation
The simulated patterns and magnitude of precipitation for this area are similar to a previous study using an earlier version of RCA, RCA3.5, without dynamic vegetation (Nikulin et al, 2012)
Summary
The Sahel greening and Congo rainforest browning observed since the 1980s suggest that Africa has been undergoing significant changes in the structure, composition and distribution of vegetation during recent decades (Eklundh and Olsson, 2003; Olsson et al, 2005; Jamali et al, 2014; Zhou et al., 2014). Shifts in vegetation cover and composition in terms of the distribution of trees and grasses and their seasonal changes (phenology) can impose significant forcings on the physical climate system by modulating surface–atmosphere energy exchange and hydrological cycling, resulting in biophysical feedbacks along with the climate forcings. Hypothesized mechanisms of vegetation–atmosphere coupling include modulations of the surface albedo (Charney, 1975), changes in the North African monsoon system (Claussen, 1997) and internal climate variability (Zeng et al, 1999)
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