The impact of deforestation on cloud cover over the Amazon arc of deforestation

Atmospheric general circulation model (AGCM) simulations predict that a complete deforestation of the Amazon basin would lead to a significant climate change; however, it is more difficult to determine the amount of deforestation that would lead to a detectable climate change. This paper examines whether cloudiness has already changed locally in the Brazilian arc of deforestation, one of the most deforested regions of the Amazon basin, where over 15% of the primary forest has been converted to pasture and agriculture. Three pairs of deforested/forested areas have been selected at a scale compatible with that of climate model grids to compare changes in land cover with changes in cloudiness observed in satellite data over a 10-year period from 1984 to 1993. Analysis of cloud cover trends suggests that a regional climate change may already be underway in the most deforested part of the arc of deforestation. Although changes in cloud cover over deforested areas are not significant for interannual variations, they are for the seasonal and diurnal distributions. During the dry season, observations show more low-level clouds in early afternoon and less convection at night and in early morning over deforested areas. During the wet season, convective cloudiness is enhanced in the early night over deforested areas. Generally speaking, the results suggest that deforestation may lead to increased seasonality; however, some of the differences observed between deforested and forested areas may be related to their different geographical locations. (C) 2003 Elsevier Science Inc. All rights reserved.