The impact of observed deforestation on the mesoscale distribution of rainfall and clouds in Amazonia

Abstract

A numerical mesoscale model has been used to investigate the impact of mesoscale circulations on the distribution of precipitation and cloudiness over a deforested area in Amazonia. Observed patterns of deforestation in Rondônia, Amazonia, with scales on the order of 10 km were used in this study to describe land surface conditions. Various simulations have been performed to identify the conditions under which the mesoscale circulations induced by the heterogeneous land surface could enhance cloudiness and local rainfall. The simulation results suggest that the synoptic forcing, in terms of atmospheric stability and background horizontal wind, dominates during the rainy season; synoptic conditions were so favorable to moist convection that the added effect of surface heterogeneity was negligible. During the dry season, a noticeable impact of mesoscale circulations resulting in enhancement of shallow clouds was simulated; the mesoscale circulations also triggered scattered deep convection that altered the spatial distribution of precipitation. During the break period, the transition from the rainy season to the dry season, the impact of mesoscale circulations on low-level clouds was evident only after reducing the magnitude of the background wind.