Fig. 1.

Sahelian rainfall–NDVI functional relationships and inferred trends in greening or degradation. (A) Best-fit functional models for 260 watersheds in Senegal, Mali, and Niger based on the cAIC. (B) Trends in vegetation condition through time in the same watersheds assessed using the residual-trend approach (36, 37), where “up” indicates increasing RUE (i.e., improving vegetation) and “down” indicates decreasing RUE (i.e., degradation). Inferences in B are reported using the linear and nonlinear functional relationships, as well as using the best models for each watershed shown in A. In general, although the majority of watersheds show modest (nonsignificant) improvements, relatively few watersheds show strong upward or downward trends. The choice of functional relationship has little impact on these results.