The Sirba is one of the two sub-basins most vulnerable to climate change in eastern Burkina Faso. Using data from ten synoptic stations operated by Burkina Faso's National Meteorological Department, we have shown that this sub-basin is undergoing progressive aridification. Hence the importance of assessing its impact on plant cover in order to prevent the survival of populations. A study restricted to the downstream part of this sub-basin, using NDVI images of spot vegetation and De Martonne's aridity index, shows that the drying out of the vegetation cover is not the only effect of this aridification. Despite increasingly abundant rainfall, the climate is aridifying under the action of temperature, ETP and various anthropogenic activities, which still require study, regulation and control by governmental institutions and international bodies. In short, the results of this study are essential for all those involved in agricultural work, climate change, GIS, humanitarian aid, forest and water resource protection, etc., in Sahelian and other countries.