In the framework of the implementation of the national action plan (NAP) as part of the UNCCD, a network of observatories for the assessment and monitoring of desertification has been established, covering the main agro-ecological zones of Tunisia. Menzel Habib represents one of the main observatories located in a typical arid zone threatened by desertification. This site is also part of the ROSELT3/OSS4 network and the arid zones observatory implemented by IRA within the framework of the national monitoring system of desertification coordinated by the national focal point of the UNCCD. It is in this framework that the GIS-based model LEIS (Local Environmental Information System) (in French known as SIEL) developed by the ROSELT team in Montpellier (Roselt/OSS, DS3, 2004) was applied to this observatory. The data used were issued from achieved and on-going multidisciplinary monitoring of the observatory covering the biophysical (soil, water, climate, vegetation) and the agro-socio-economic (population, agriculture and pasture practices, land uses, etc.) aspects. Three types of information were used: remotely sensed data (satellite images), field measurements (vegetation bio-mass, yields, GPS, etc.), and socio-economic surveys (households, income, activi ties, etc.). Multiple scenarios have been conducted to assess the impact of changing one or many parameters (population, livestock, etc.). In fact, the final objective of the model is to place at the disposal of the various actors of development, research ers and technicians, a Spatial Decision Support System (SDSS) for planning and monitoring in plans to combat desertification and natural resources management in the dry areas.