Empirical Assessment of Radiative Forcing by Biomass Burning Aerosols Over the Middle Belt During the Burning Season

Agricultural biomass burning across Nigeria's Middle Belt states (Benue, Kogi, Kwara, Nassarawa, and Niger) during the dry season releases significant quantities of aerosols and trace gases that alter the regional radiation budget and cloud microphysics. This study empirically assesses the radiative forcing of biomass burning aerosols over the Middle Belt during the November to March burning season using MODIS aerosol and fire count products, AERONET photometric measurements, and radiative transfer model simulations. Biomass burning aerosol optical depth (BB-AOD) was separated from total AOD using the MODIS fire radiative power product as a burning intensity proxy. The SBDART radiative transfer model was used to compute instantaneous shortwave direct radiative forcing at the surface and top of atmosphere for identified burning episodes. Fire count data from MODIS Active Fire product show that burning intensity peaks in January and February, with Benue and Niger states contributing 62 percent of total fire pixels across the study region. BB-AOD values during peak burning periods average 0.68 at 550 nanometres, corresponding to surface shortwave radiative forcing of minus 18 to minus 28 watts per square metre. Significant positive correlations between burning season aerosol loading and temperature anomalies in the weeks following burning episodes suggest delayed surface heating through absorbing aerosol dynamics. The study recommends regulation of burning practices and integration of fire aerosol monitoring into NiMet's climate monitoring program for the Middle Belt. Keywords: biomass burning, aerosol, radiative forcing, Middle Belt, MODIS.