The implication of atmospheric aerosols on rainfall over Malawi, Southeast Africa

Abstract

Understanding the driving factors for the change of climatic patterns is crucial for the implementation of mitigation and adaptation measures. Significant effort has been made to understand changes in climatic patterns; however, less has been done to investigate the driving factors that influence the trends of early rainfall over Malawi. Hence, a substantial research gap exists concerning in the implementation of mitigation and adaptation measures. The present study investigates the implications of atmospheric aerosols on precipitation during the early rainfall season over Malawi. Open burning, such as bushfires and burning of crop residues by local farmers, are the major anthropogenic activities enhancing aerosol accumulation in the atmosphere and hence need to be strictly controlled over the domain and the surrounding region. The present results show that rainfall generally starts between October and November and gradually increases with the maximum observed in January and ends in March in most areas. Monthly aerosol optical depth (AOD₅₅₀) has an opposite pattern to that of rainfall with high AOD₅₅₀ (>0.4) between September and October, mostly over southern areas and along with Lake Malawi. An analysis of rainfall during the beginning of the season indicates a significant decrease of rainfall over the southern areas of Malawi, associated with high AOD₅₅₀, while insignificant change is observed over the central and northern areas associated with low AOD₅₅₀ values. Statistical analyses among AOD₅₅₀, cloud effective radius (CER), and precipitation demonstrates that negative trends of rainfall are strongly associated with a high concentration of anthropogenic aerosols from biomass burning during October. These aerosols might have absorbed excess moisture and disrupted local convective processes associated with the first rainfall that the domain receives, between the months of October and November. Therefore, regional control measures are required to reduce the excess emissions of anthropogenic aerosols into the atmosphere, such as controlling open burning during the active fire period (July-October).