The Hydrometeorology of a Deforested Region of the Amazon Basin

Abstract

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 land?atmosphere interactions taking place in that region. Overall, it is demonstrated that RAMS can simulate properly the domain-average accumulated rainfall in Rondônia, Brazil, 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. However, 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 horizontal grid elements 2 and 4 km in size show a delay and decrease of rainfall as compared to simulations with high-resolution grids whose elements are not larger than 1 km and, as a result, afflict RAMS performance. It is concluded that RAMS can be used as a reliable tool to simulate the various hydrometeorological processes involved in land-cover changes as a result of deforestation in this region.