Patterns of shallow clouds and rainfall over the Amazon : climatic impacts of deforestation

Abstract

(cont.) and, to a lesser extent, cold cloud patterns over the Amazon. Through complex interactions, the results reported in this thesis may have important implications for the local ecosystem dynamics of the Amazon, for the geomorphology of the Amazon river basin, for the flow regimes of the Amazon river, and for global climate.

The climatic impact of the current state of deforestation in the Amazon basin is examined in this thesis. Past modeling studies have shown that complete deforestation of the Amazon basin could result in dramatic decreases in regional rainfall and evaporation leading to desertification (e. g., Salati and Vose [1984], Shukla et al. [1990]). Yet, although 15% of the 4,000,000 km² Brazilian Amazon has already been deforested [INPE, 2003], current deforestation patterns in the Amazon basin are not uniform, nor do their extents surpass tens of kilometers. Numerical simulations indicate that idealized heterogeneities of land-surface properties could lead to organized mesoscale circulations that enhance convection (e. g., Anthes [1984], Chen and Avissar [1994a], Avissar and Liu [1996], Wang et al. [1998]); similar results were found in case-study simulations of actual Amazon deforestation (e. g., Wang et al. [2000], Roy and Avissar [2002]). Qualitative observations of enhanced shallow cloud cover over cleared areas have provided preliminary indications of episodic land-cover-driven mesoscale circulations in the Amazon basin (e. g., Cutrim et al. [1995], Durieux et al. [2003], Negri et al. [2004]). Based on these studies, the effects of the "fishbone" patterns of deforestation on shallow vection were thought to occur only episodically during few precious weeks toward the end of the dry season, and were largely accepted as being climatically insignificant. However, through the use of satellite data from the Geostationary Operational Environmental Satellite (GOES) and the Tropical Rainfall Measuring Mission (TRMM), this thesis quantitatively demonstrate that the complex pattern of deforestation in the Amazon has resulted in a climatic shift in shallow cloud, rainfall