Implications of tropical deforestation for climate: a comparison of model and observational descriptions of surface energy and hydrological balance

Abstract

Quantitative estimates of the impacts of tropical deforestation on climate can only be considered through use of models of climate that contain adequate treatments of both the land and atmospheric components. Recent global climate model (GCM) calculations by Dickinson & Henderson-Sellers of the effect of removing the Amazon forest attempted to include a detailed canopy model of the forest and the assumed grass replacement. An important role for the structure of the forest canopy was suggested by this study. However, data of Shuttleworth on the seasonal variation of Amazon evapotranspiration show much lower values during the wet season than were obtained in the GCM study and, consequently, much less seasonal variation. The reason for this discrepancy is examined by using results both from the GCM used in the deforestation study and a three-year simulation with a more recent version. The major source of the discrepancy is found to be a large excess of net surface radiation in the GCM simulations, and an excess rainfall interception loss, which is a consequence of this excess radiation. The modelled transpiration appears to agree with the observations.