Effects of vegetation composition changes on surface runoff and land degradation in Sahelian Watersheds

The relationship between vegetation composition and surface runoff remains unstudied in the Sahel – a region with unique hydrological characteristics compounded by land degradation. This study investigates the effects of vegetation composition changes on runoff and land degradation trends in 45 Sahelian watersheds over two decades (2001–2020). Vegetation composition was assessed using vegetation continuous fields (VCFs) including tree canopy cover (TC), short vegetation cover (SV) and bare ground cover (BG) while vegetation cover was measured using the normalized difference vegetation index (NDVI). The analysis revealed significant increasing trends in annual NDVI across most watersheds, accompanied by gains in TC (mean = 1%) and SV (mean = 3%), and a decline in BG (mean = −6%) – indicating a reversal in land degradation. Results also showed that runoff is extremely sensitive to changes in vegetation composition parameters. These findings offer valuable insights for ecological restoration through the strategic selection of tree species to regulate surface runoff effectively.