The Congo basin as an outlier in the tropical upward mass transport

The Congo Basin is one of the world’s three major tropical convective hotspots, yet it receives substantially less rainfall than the Amazon and the Maritime Continent, despite exhibiting the highest lightning activity globally. This paradox points to fundamental differences in convective structure and rainfall efficiency. Here, we investigate the vertical structure of convection over Central Africa using upward mass transport as a proxy, and examine its relationship with precipitable water and moist static energy (MSE). We show that during the rainy season, convection over the Congo Basin is characterized by a bottom-heavy vertical mass flux profile, accompanied by strong moisture advection in the lower to mid-troposphere. This structure contrasts sharply with the deeper, more top-heavy convective profiles observed over the Amazon and the Maritime Continent, indicating a predominance of relatively shallow convective systems.

Analysis of the MSE distribution reveals high values near the surface, reflecting substantial energy available for convective initiation, while lower MSE aloft is consistent with latent heat release and buoyancy generation within ascending parcels. Together, these results suggest that although the thermodynamic environment over the Congo Basin is highly favorable for triggering convection, the vertical redistribution of mass and energy acts to constrain convective depth and suppress rainfall efficiency. These processes are poorly represented, or entirely missing, in historical CMIP6 Earth system models. Our findings therefore highlight a distinct convective regime over the Congo Basin, with important implications for understanding tropical precipitation and for improving its representation in climate models.