DETECTING CLIMATE-CHANGE CONCURRENT WITH DEFORESTATION IN THE AMAZON BASIN - WHICH WAY HAS IT GONE

To detect climate change in the Amazon Basin, as possibly induced by d eforestation, time series of monthly mean outgoing longwave radiation (OLR), an index of tropical convection, and monthly rainfall totals at Belem and Manaus for the past 15 years are analyzed. A systematic bia s in the original OLR series was removed prior to the analysis. Linear regression analysis and nonlinear Mann-Kendall rank statistic are emp loyed to detect trends. Over almost all of the basin, the OLR trend va lues are negative, indicating an increase of convection with time. The largest negative and statistically significant values are found in th e western equatorial portion of Amazonia, where rainfall is most abund ant. Consistent with this, the rainfall series at Belem and Manaus als o feature upward trends. Small positive and statistically insignifican t, OLR trend values are confined to the southern fringe of the basin, where deforestation has been most drastic. Thus, there is little indic ation for a rainfall increase associated with deforestation, but rathe r a strong signal of enhanced convection in the portion of Amazonia co ntributing most strongly to the total precipitation over the basin.