RCCM2-BATS MODEL OVER TROPICAL SOUTH-AMERICA - APPLICATIONS TO TROPICAL DEFORESTATION

A multiyear simulation of the global climate uses a revised version of the National Center for Atmospheric Research (NCAR) Community Climate Model Version 2 (CCM2) coupled to the Biosphere-Atmosphere Transfer S cheme (BATS). It is compared with global and rain gauge precipitation climatologies to evaluate precipitation fields and European Centre for Medium-Range Forecasts analyses to evaluate the atmospheric circulati on. The near-surface climate is compared with data from Amazonian fiel d campaigns. The model simulation of the South American climate agrees closely with the observational record and is much improved from past simulations with previous versions of the NCAR Community Climate Model over this portion of the Tropics, The model is then used to study the local and regional response to tropical deforestation over Amazonia. In addition to the standard deforestation forcing. consisting mainly o f increased albedo and decreased roughness length, two additional sens itivity experiments were conducted to assess the individual contributi ons from these forcings to the deforestation changes. The standard def orestation simulation shows slight increases in annually averaged surf ace temperature (+1 degrees C) and reductions in annually averaged pre cipitation and evaporation (-363 and -149 mm yr(-1), respectively). As expected. increases in surface albedo over Amazonia produce a reducti on in net downward solar radiation at the surface and consequently a r eduction in net surface radiation and surface latent heat flux. The ro ughness decrease, on the other hand, reduces the surface latent heat f luxes through decreases in the surface drag coefficient. The regional changes in moisture convergence and precipitation during the Amazonian wet season display a shift in the area of maximum precipitation rathe r than an overall decrease over the deforested area. These shifts are evidently produced by a combination of the changes in the low-level ci rculation and a decrease in the efficiency of precipitation recycling within Amazonia.