Assessing the Impact of the Sahel Greenbelt on Sahelian Moist Static Energy: Vertical Structure and Zonal Distribution

The climate impact of the Sahel greenbelt on regional moist static energy (MSE) and West African Monsoon energetics remains insufficiently understood. Using a 30-year equilibrium simulation applying the CESM2 model, we use a column-integrated MSE budget framework to diagnose the response to a 70% vegetation increase over the Sahel (10˚N - 18˚N). Results demonstrate that greenbelt forcing shifts the MSE maximum poleward from 5˚N - 12˚N to 15˚N - 18˚N, increasing core values over the central Sahel from 1.254 to 1.507 kJ·kg−1. This northward expansion is driven by enhanced evapotranspiration (+4.33 W·m−2 latent heat flux), which repartitions surface energy from sensible to latent heat dominance, moistening the boundary layer. Dynamically, strengthened low-level westerlies transport warm, moist air from the tropical Atlantic deeper into the eastern Sahel, while reduced northeasterly dry advection and a weakened, northward-shifted African Easterly Jet minimize dry mid-tropospheric intrusion and favor vertical MSE transport. Column-integrated MSE increases by 7.2 W·m−2 north of 15˚N. Budget decomposition reveals that circulation-driven advection accounts for nearly two-thirds of this increase, with vertical advection as the dominant contributor (43%), efficiently transporting high-MSE air to the free atmosphere. Mean horizontal flow exports energy, partially offset by anomalous wind import. The atmospheric energy surplus (+7.67 W·m−2) is primarily fueled by enhanced shortwave absorption and latent heat flux. Overall, vegetation recovery drives a thermodynamic regime shift from sensible to latent heat dominance, promoting northward expansion of Sahelian MSE and providing a mechanistic basis for evaluating large-scale reforestation as a regional climate adaptation strategy.