Troprcal Deforestation: Modeling Local- to Regional-Scale Climate Change

A. HENDERSON-SELLERS, R. E. DICKlNSON, T. B. DURBIDGE, P. J. Kennedy, K. MCGUFFIE, 
AND A. J. PITMAN 

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forest throughout the Amazon Basin and SE Asia has been replaced by scrub grassland 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 l), 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 I 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) .