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

A tropical deforestation experiment has been conducted in which the tr opical moist forest throughout the Amazon Basin and SE Asia has been r eplaced by scrub grassland in a version of the National Center for Atm ospheric Research Community Climate Model (Version 1), which also inco rporates a mixed layer ocean and the Biosphere-Atmosphere Transfer Sch eme. In both regions we find a smaller temperature increase than did a ll other previous experiments except that of Henderson-Sellers and Gor nitz (1984); indeed, temperatures decrease in some months. On the othe r hand, we find larger runoff decreases and a larger difference betwee n the changes in evaporation and precipitation than all earlier experi ments indicating a basin-wide decrease in moisture convergence. Distur bances in South America extend beyond the region of land-surface chang e causing temperature reductions and precipitation increases to the so uth of the deforested Amazon. Changes to the surface climate in the de forested area take between 1 to 2 years to become fully established al though the root zone soil moisture is still decreasing in year 3 and t he variability of soil moisture and total cloud amount continue increa sing throughout the 6-year integration. Besides temperature and precip itation, other fields show statistically significant alterations, espe cially evaporation and net surface radiation (both decreased).