Examining the relationship between aerosol concentration and observed mean temperatures over Uganda

Abstract

The aerosol load over the world is increasing because of both human activities and natural forcing, though human induced factors such as mining activities, vehicular emissions and industrial emissions have been identified as the biggest contributors to the aerosol load. Sub Saharan Africa has experienced persistent exposure to aerosol from time immemorial, but the intensity has been much more severe in recent years. The main objective was to contribute to the study of how aerosol concentration affect temperatures over Uganda, this study used the mean monthly Aerosol Optical Depth data and mean monthly temperature data from Climatic Research Unit to give a 30-year understanding of the relationship. The first objective was to determine the spatial and temporal trends of temperatures in Uganda from 1991 to 2020 and it was observed that the mean annual temperature over Uganda followed a positive insignificant trend (P =0.075). MAM was found to be the hottest month and it was 0.030C hotter than the DJF. SON and JJA were the coolest seasons although SON temperatures was found 0.50C hotter than JJA. The second objective was to determine the spatial and temporal distribution and areas of aerosol hotspot concentration in Uganda from 1991 to 2020 and it was found to be increasing significantly with a P-value (P =0.037). The wet seasons exhibited low aerosol optical depth concentration than the dry seasons (JJA and DJF) and spatially it stretched longitudinally from Western to Eastern with more aerosol optical depth concentration in the West. The Central, South, Central North and North Eastern Uganda had moderate aerosol optical depth. Eastern region exhibited the lowest aerosol optical depth. The third objective was to establish a relationship between aerosol optical depth and mean temperature which was found to be significant at both inter-annual and seasonal time scales with P values far less than 0.05 and that aerosol optical depth explained 7.7% of the mean temperature over Uganda as revealed by the P value in table 4.4.