Modeling the short-term fire effects on vegetation dynamics and surface energy in Southern Africa using the improved SSiB4/TRIFFID-Fire model

Abstract. Fire causes abrupt changes in vegetation properties and modifies flux exchanges between land and atmosphere at subseasonal to seasonal scales. Yet these short-term fire effects on vegetation dynamics and surface energy balance have not been comprehensively investigated in the vegetation model coupled with the fire module. This study applies the SSiB4/TRIFFID-Fire model to study the short-term fire impact in Southern Africa with comprehensive evaluations of simulated fire regimes, vegetation productivity, and surface fluxes. We find an annual average reduction in grass cover by 4–8 % for widespread areas between 5–20° S and a tree cover reduction by 1 % at the southern periphery of tropical rainforests. The fire effects on regional scales accumulate during June–October and peak in November, the beginning of the rainy season. After the fire season ends, the grass cover quickly returns to unburned conditions before the next fire season, while the tree fraction hardly recovers in one rainy season. The vegetation clearance by fire has reduced the leaf area index (LAI) and gross primary productivity (GPP) by 3–5 % and 5–7 % annually, respectively. The exposure of bare soil has enhanced surface albedo and therefore decreased the absorption of shortwave radiation. Annual mean sensible heat has dropped by 1.4 W m−2 while the latent heat reduction is small (0.1 W m−2) due to the compensating effects between canopy transpiration and soil evaporation. A slight warming effect is simulated after fire, which could be enhanced when the surface darkening effect is incorporated.