In a recent study in Nature Climate Change Haywood and colleagues demonstrate how volcanic eruptions can influence Sahelian precipitation. Sadly the article is not open access, but from the abstract it seems like they are providing further evidence that aerosols are important for rainfall in the Sahel. In this context I also recommend the study by Huang which shows how black carbon also is a player in this game.
Haywood and colleagues suggest that sporadic volcanic eruptions in the Northern Hemisphere cause Sahelian drought. Using de-trended observations from 1900 to 2010, they show that three of the four driest Sahelian summers were preceded by substantial Northern Hemisphere volcanic eruptions. They used a state-of-the-art coupled global atmosphere–ocean model to simulate both episodic volcanic eruptions and geoengineering by continuous deliberate injection into the stratosphere. In either case, large asymmetric stratospheric aerosol loadings concentrated in the Northern Hemisphere were a harbinger of Sahelian drought whereas those concentrated in the Southern Hemisphere induce a greening of the Sahel.