Evidence of Fire-Induced Rainfall Modification in sub-Saharan Africa

Abstract:

Recent studies have highlighted the importance of the land surface in promoting or inhibiting convective development and precipitation. At the same time, fire represents a dramatic, instantaneous shift in energy and mass fluxes at the surface. We examine the role that fires play in modifying subsequent precipitation on seasonal timescales across sub-Saharan Africa. Using MODIS burned area product and TRMM daily precipitation we find that fire suppresses total wet season accumulated rainfall in arid and semiarid regions. In the regions receiving less than 500 mm of mean annual precipitation (MAP) this suppression amounts to deficits of up to 30% of MAP. This observed pattern is consistent between drylands in both hemispheres. We consider the possible mechanisms of fire-induced rainfall suppression, including changes in albedo and reduced evapotranspiration. We propose a novel feedback between rainfall and fire that is manifested by an oscillation between low rainfall and high rainfall years. Observational evidence supports this hypothesis. Finally, using MODIS land cover data we find that the regions where we observe fire-induced rainfall suppression are comprised of a higher than expected proportion of croplands and cropland mosaic. We highlight the possibility of a novel anthropogenic influence on hydrologic cycling in regions where water resources are scarce.