Amazonia deforestation and climate : past, present and future / by Renato Ramos da Silva.

Tese (Ph.D.) - Duke University, 2006

The Amazon is the largest hydro-meteorological system on Earth. Recent anthropogenic land-cover changes have replaced nearly 20% of the forest into degraded vegetation. In this study, I use a state-of-the-art model to understand the impacts of deforestation on the local hydrometeorology. A series of numerical simulations were performed to evaluate the capability of the Regional Atmospheric Modeling System (RAMS) to simulate the evolution of convection in a partly deforested region of the Amazon basin during the rainy season, and to elucidate some of the complex landatmosphere interactions taking place in that region. Overall, RAMS can simulate properly the domain-average accumulated rainfall in Rondônia when provided with reliable initial profiles of atmospheric relative humidity and soil moisture. It is also capable of simulating important feedbacks involving the energy partition at the ground surface and the formation of convection. In general, more water in the soil and/or the atmosphere produces more rainfall. But these conditions affect the onset of rainfall in opposite ways; while higher atmospheric relative humidity leads to early rainfall, higher soil moisture delays its formation. As compared to stratiform clouds, which tend to cover a large area, convective clouds are localized and they let relatively more solar radiation reach the ground surface. As a result, a stronger sensible heat flux is released at the ground surface, which enhances the atmospheric instability and reinforces convection. Simulations using realistic scenarios of landscape change for the entire basin show that rainfall decreases mostly in the western part of the basin because the large squall-lines moving from the northeastern to the southwestern part of the basin, which are responsible for most of the precipitation in that region, dissipate before reaching it. This is particularly true during dry years (e.g., El Niño years). However, the eastern -- and to a slightly lesser extent, the southern -- part of the basin is much less affected by the deforestation and sees even an increase of precipitation during dry years.