Global analysis of radiative forcing from fire-induced shortwave albedo change

Abstract. Land surface albedo, a key parameter to derive Earth's surface energy balance, is used in the parameterization of numerical weather prediction, climate monitoring and climate change impact assessments. Changes in albedo due to fire have not been fully investigated at continental and global scale. The main goal of this study therefore, is to quantify the changes in albedo produced by biomass burning activities and their associated shortwave radiative forcing. The study relies on the Moderate Resolution Imaging Spectroradiometer (MODIS) MCD64A1 burned area product to create an annual composite of areas affected by fire and the MCD43C2 BRDF-Albedo snow-free product to compute a bihemispherical reflectance time series. The approximate day of burn is used to calculate the instantaneous change in shortwave Albedo. Using the corresponding National Centers for Environmental Prediction (NCEP) monthly mean downward solar radiation flux at the surface, the global radiative forcing associated to fire was computed. The analysis reveals a mean decrease in shortwave albedo of −0.023 (1σ = 0.018) causing a mean positive radiative forcing of 6.31 W m–2 (1σ = 5.04) over the 2002–2012 time period in areas affected by fire. The greatest drop in mean shortwave albedo change occurs in 2002, which corresponds to the highest total area burnt (3.66 Mha) observed in the same year and produces the highest mean radiative forcing (6.75 W m–2). Africa is the main contributor in terms of burned area but forests globally are giving the highest radiative forcing per unit area, thus give detectable changes in shortwave albedo. The global mean radiative forcing for the whole studied period ~ 0.04 W m–2 shows that the contribution of fires into the Earth system is not insignificant.