Socio-ecohydrological interactions in Sahelian watersheds

Background/Question/Methods

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 used 40-years (1972-2011) of remotely sensed data to explore socio-ecohydrological interactions in the watersheds surrounding 260 ponds in the Sahel. Rainfall, vegetation greenness, cropping intensity and livestock density were analyzed to investigate their potential role in determining pond areas as a function of watershed size and geomorphology. Analyses focus on 4 analysis regions (Southwestern Niger, Eastern Mali, Western Mali and Northern Senegal) representing a range of bioclimatic, edaphic and land use conditions.

Results/Conclusions

During the 1972-2011 period, we found that: (i) ponds areas displayed a remarkable expansion with the flood of ephemeral ponds extending longer into the dry season and some ponds becoming perennial, (ii) pond area responds positively to an increase of the amount of rainfall and the number of livestock, and also to a decrease of vegetative greenness and the extent of crop fields, (iii) the increase of pond area is less pronounced over less gravelly watersheds.