TROPICAL DEFORESTATION - MODELING LOCAL-SCALE TO REGIONAL-SCALE CLIMATE CHANGE

A tropical deforestation experiment has been conducted in which the tropical moist forest throughout the Amazon Basin and SE Asia has been replaced by scrub grassland in a version of the National Center for Atmospheric Research Community Climate Model (Version 1), which also incorporates a mixed layer ocean and the Biosphere-Atmosphere Transfer Scheme. In both regions we find a smaller temperature increase than did all other previous experiments except that of Henderson-Sellers and Gornitz (1984); indeed, temperatures decrease in some months. On the other hand, we find larger runoff decreases and a larger difference between the changes in evaporation and precipitation than all earlier experiments indicating a basin-wide decrease in moisture convergence. Disturbances in South America extend beyond the region of land-surface change causing temperature reductions and precipitation increases to the south of the deforested Amazon. Changes to the surface climate in the deforested area take between 1 to 2 years to become fully established although the root zone soil moisture is still decreasing in year 3 and the variability of soil moisture and total cloud amount continue increasing throughout the 6-year integration. Besides temperature and precipitation, other fields show statistically significant alterations, especially evaporation and net surface radiation (both decreased).