Two Decades of Fire-Induced Albedo Change and Associated Short-Wave Radiative Effect Over Sub-Saharan Africa

Abstract

We present an analysis of 20 years of fire and albedo data in Africa. We show that, in the mean, the sub-Saharan Africa post-fire surface albedo anomaly can be parameterized using an exponential recovery function, recovering from a decrease of $0.019\pm 0.001$ immediately after a fire with a time constant of $34.0\pm 0.4$ days. Although the magnitude of albedo changes shows large spatial and temporal variations and a strong land cover type (LCT) dependency, exponential recovery is observed in the majority of LCTs. We show that fires cause long-term surface brightening, with an Africa-wide albedo increase of $\left(9.5\pm 0.2\right)\times 10^{-4}$ 10 months after a fire, but we find this is driven almost exclusively by slow vegetation recovery in the Kalahari region, confirming previous findings. Using downward surface shortwave flux (DSSF) estimates, we calculate the fire-induced surface radiative forcing (RF), peaking at $5\pm 2$ Wm⁻² in the burn areas, albeit with a significantly smaller effect when averaged temporally and spatially. We find that the long-term RF in months 5–10 after a burn averaged over the continent is negative because of the brightening observed. Despite a well-documented reduction in burning in Africa in the recent decades, our temporal analysis does not indicate a decrease in the overall fire-induced RF likely due to large interannual variability in albedo anomaly and DSSF data. However, we observe a decline in the short-term RF in southern hemisphere Africa, driven by both a reduction in fires and changes in LCT distributions.