Assessing the role of deep rooted vegetation in the climate system with model simulations: mechanism, comparison to observations and implications forAmazonian deforestation

Deep rooted vegetation (of up to 68 m) has been found in many parts of the tropics. However, models of the general atmospheric circulation (GCMs) typi cally use rooting depths of less than 2 m in their land surface parametriza tions. How does the incorporation of deep roots into such a model affect th e simulated climate? We assess this question by using a GCM and find that d eeper roots lead to a pronounced seasonal response. During the dry season, evapotranspiration and the associated latent heat flux are considerably inc reased over large regions leading to a cooling of up to 8 K. The enhanced a tmospheric moisture is transported towards the main convection areas in the inner tropical convergence zone where it supplies more energy to convectio n thus intensifying the tropical circulation patterns. Comparison to differ ent kinds of data reveals that the simulation with deeper roots is much clo ser to observations. The inclusion of deep roots also leads to a general in creased climatic sensitivity to rooting depth change. We investigate this a spect in the context of the climatic effects of large-scale deforestation i n Amazonia. Most of the regional and remote changes can be attributed to th e removal of deep roots. We conclude that deep rooted vegetation is an impo rtant part of the tropical climate system. Without the consideration of dee p roots, the present-day surface climate cannot adequately be simulated.