The main objectives of the AMMA project are to better understand the West African Monsoon and its variability, and to improve the predictions of the impacts of this variability on West African societies. One of the preliminary stages necessary for analysing such impacts on agriculture and food security is a reliable estimation of the cultivated domain at national level, a scale compatible with climate change sn1dies. This study was conducted by the CIRAD, in order to evaluate if free moderate-resolution satellite data, in combination with external data (thematic maps, statistics, etc.) can provide a correct assessment of the distribution of the cultivated domain at country level. A methodology was developed to extract cultivated areas based on their temporal behaviour as captured in time-series of MODIS/TERRA images. We applied this methodology in Senegal and Mali. We showed through this study that a comprehensive stratification of the area is a decisive step in the classification procedure, leading to a map of the cultivated areas at a national scale. Using medium resolution satellite images helps to monitor with continuity Sahelian rural landscapes, and consequently to provide relevant infom1ation for early warming system. We showed that medium spatial resolutions do not, by themselves, provide a completely satisfactory representation of the landscape but are compensated for by a large coverage area and by an excellent temporal resolution. We are now studying the contribution of other resolution data in term of land cover assessment and the benefit of crossing ail these different kinds of information.