Ecohydrological Relationships in Dryland Grazing Systems of the Sahel

In water-limited environments like the Sahel, rangelands function as strongly coupled ecological-hydrological systems. Rainfall and soil moisture availability are the main forces driving vegetation structure and composition, and vegetation exerts strong controls on the redistribution and infiltration of rainfall. The presence and duration of surface waters in the landscape, however, determines livestock access to and consumption of pasture resources, with feedbacks on vegetation structure and ecohydrology. In this study, we use the Tree Grass Vegetation Model (TGVM) to study the interactions between climate, vegetation, grazing and lake volume in the watersheds surrounding 260 ponds in the Sahel. Analyses focus on 4 regions (Southwestern Niger, Eastern Mali, Western Mali and Northern Senegal) representing a range of bioclimatic, edaphic and land use conditions and were performed during the period 1972-2011. Unsupervised land cover classification maps using Landsat time series data were used to provide soil information, assuming a strong correlation between vegetation type and the underlying soil type, and the curve number method was used to estimate runoff during rainfall. We will explore the socio-ecohydrological relationships in response to grazing disturbances and climate variability, and discuss how feedbacks mediated by anthropogenic control of herbivore density could be significant for the sustainable management of Sahelian and other dryland regions.