Effects of emissions on current and future rainfall patterns in southeast Brazil

Resumo

This project will be the first observation-based investigation of the climate change feedbacks involving precipitation, cloud formation and aerosols in the South American rural subtropics (southeast Brazil). The region is a natural laboratory for such a study, due to large differences in seasonal weather patterns, with distinct wet and dry periods, and well-defined sources of anthropogenic aerosols, especially agricultural biomass burning. Previous work has reported intensification of storms over large cities, due to the presence of aerosols of anthropogenic origin; here we will investigate the extent to which a similar mechanism operates in rural areas, and how it might affect the distribution and intensity of precipitation. Future changes in the nature of the region's atmospheric aerosol - the direct and indirect aerosol climate forcing are likely to diminish here, due to progressive restrictions on biomass burning - will affect this mechanism, and therefore influence the hydrological cycle, with consequences for water resources in agriculture, hydroelectricity and industrial and domestic supply. Measurements in central São Paulo State will identify coherences between the frequency, distribution and intensity of precipitation (using S-band Doppler radars), aerosol number concentrations and size distributions, the frequency of cloud to ground electrical discharges, and cloud droplet effective radius. Intensive experiments will then link aerosol physical properties with particle chemistry. Knowledge of particle chemistry will be used to identify aerosol sources (using receptor modeling). We will then be able to build conceptual models describing the influence of different aerosol classes on precipitation, and the impact of human activities. The influence of agricultural production methods on precipitation patterns will be investigated, with special emphasis on the pre-harvest burning of sugar cane, which is of interest from both climatic and human heath perspectives. (AU)