Large-scale hydrological responses to tropical deforestation

Deforestation, especially tropical deforestation, is a geopolitical issue: tropical forests contain the vast majority of the world's species, deforestation contributes about 20% of the current flux of carbon dioxide to the atmosphere, and, it is often argued, that sustainable agriculture is impossible in these regions. Two regions have been particularly identified as areas where the impacts of the extensive removal of moist, tropical forest are potentially critical to the sustained activities of humans; these are the Amazon basin in South America and Southeast Asia. These regions contain the largest, contiguous tropical forest resource remaining on Earth and play essential roles in the regional climate and hydrology. The deforestation of the Amazon region has been the subject of a number of previous investigations which differ significantly in experimental design and results. Therefore part of this research provides further insight into the understanding of the consequences of deforestation. As a first step to extending these deforestation investigations, the Southeast Asian region presents a useful arena to examine model sensitivities to the different surface and atmospheric features and permits insight into the teleconnections that exist between the regions at a global scale. Results show that two elements of the macroscale hydrosphere are impacted by tropical deforestation in Southeast Asia: evaporation is significantly decreased while surface runoff is increased. In addition, we find a weakening in the Hadley circulation over the deforested area of Southeast Asia. The Walker circulation is most strongly affected in July when the Atlantic and east Pacific cells are replaced by large-scale descending motion from ~ 140°W to ~ 100°E.