Speaker: Rong Fu from UCLA

Title: "How do rainforests and biomass burning aerosols affect rainy season onsets over tropical continents?"

Abstract:  Amazon and Congo rainforest regions have experienced unusually frequent extreme droughts, and strong delays of their wet-season onset and consequent lengthening of the biomass burning season, changes that are much larger than that which can be explained by oceanic variability, or can be represented by global climate models. To what extent vegetation-climate feedbacks and biomass burning aerosols contribute to such large rainfall variability is still unclear. One of the limiting factors is that its observational evidence is largely based on local or instantaneous relationships, whereas rainfall climate variability tends to be dominated by large-scale dynamics of the physical climate system. To bridge this gap, we will report our research on the influence of vegetation and biomass burning aerosols on initiating, and on weakening or strengthening the large-scale atmospheric dynamic processes that control the evolution of the rainy season onsets. Our results suggest that, by set in motion the feedbacks between anomalies of shallow and deep convection, latent heating and moisture transport, relatively moderate changes of evapotranspiration and biomass burning aerosols during the dry to wet transition can influence large-scale atmospheric circulation and rainfall on a seasonal scale. How these feedbacks influence drought duration and intensity will also be discussed.