CLIMATIC IMPACT OF AMAZON DEFORESTATION - A MECHANISTIC MODEL STUDY

Recent general circulation model (GCM) experiments suggest a drastic c hange in the regional climate, especially the hydrological cycle, afte r hypothesized Amazon basinwide deforestation. To facilitate the theor etical understanding of such a change, we develop an intermediate-leve l model for tropical climatology, including atmosphere-land-ocean inte raction. The model consists of linearized steady-state primitive equat ions with simplified thermodynamics. A simple hydrological cycle is al so included. Special attention has been paid to land-surface processes . In comparison with previous simple modeling Work on tropical climato logy or anomalies, the present model is more sophisticated in predicti ng, with little input, most of the important meteorological variables; nevertheless, it is computationally simple. It generally better simul ates tropical climatology and the ENSO anomaly than do many of the pre vious simple models. The climatic impact of Amazon deforestation is st udied in the context of this model. Model results show a much weakened Atlantic Walker-Hadley circulation as a result of the existence of a strong positive feedback loop in the atmospheric circulation system an d the hydrological cycle. The regional climate is highly sensitive to albedo change and sensitive to evapotranspiration change. The pure dyn amical effect of surface roughness length on convergence is small, but the surface flow anomaly displays intriguing features. Analysis of th e thermodynamic equation reveals that the balance between convective h eating, adiabatic cooling, and radiation largely determines the defore station response. Studies of the consequences of hypothetical continuo us deforestation suggest that the replacement of forest by desert may be able to sustain a dry climate. Scaling analysis motivated by our mo deling efforts also helps to interpret the common results of many GCM simulations. When a simple mixed-layer ocean model is coupled with the atmospheric model, the results suggest a 1 degrees C decrease in SST gradient across the equatorial Atlantic Ocean in response to Amazon de forestation. The magnitude depends on the coupling strength.