Professor Bras' Publications & Abstracts
[1] Chagnon, F.J.F. and R.L. Bras Contemporary Climate Change the Amazon Geophysical Research Letters (2005)
Deforestation of the entire Amazon basin --- the catastrophe scenario --- is projected to result in regional decreases of precipitation and evaporation, potentially leading to sustained desertification. However, current levels and patterns of Amazon deforestation actually enhance mass and energy transfers between the land and the atmosphere through the creation of thermally driven circulations. The climatological effects of these circulations have long been thought to be inconsequential (e.g., Negri et al., 2004). In contrast, we find here that current deforestation causes a dramatic change in climatological rainfall occurrence patterns; high-resolution satellite precipitation measurements show significantly more rainfall occurrences (p <0.0001) over deforested areas. Moreover, a 75 year-long rain gauge record shows a long-term shift in the seasonality of precipitation that is concurrent with deforestation. These findings suggest that current deforestation in the Amazon has already altered the regional climate. Such changes have implications for regional ecosystem dynamics, but may also affect global climatic patterns through tropospheric teleconnections.
[2] Chagnon, F.J.F., R.L. Bras, and J. Wang Climatic shift in patterns of shallow clouds over the Amazon Geophysical Research Letters (2004)
The Amazon rainforest has undergone dramatic changes in the past 50 years due to active deforestation. As of 2001, 15% of the 4,000,000 km2 Brazilian Amazon has been deforested (INPE, 2003); each year, agricultural exploitation claims an estimated 13,000 km2 of tropical forest (Achard et al., 2002). In this paper, we investigate the climatic effects caused by the observed change of the physical characteristics of the land surface (i.e., increased surface albedo, decreased root-zone depth, decreased surface roughness and decreased leaf-area index). More precisely, we examine the spatial correspondence of shallow cumulus clouds with deforestation. Through the creation of an 8-year record of thrice-daily shallow cumulus clouds at 1 km resolution from multi-spectral satellite imagery, we quantitatively show the existence of a significant climatic shift in shallow cloudiness patterns associated with deforestation. This shift manifests itself by an enhancement of shallow cumuli over deforested patches, and has potentially important climatic, hydrologic and ecological ramifications.