Résumé
The Kairouan Plain in central Tunisia, like many regions of the Maghreb, is experiencing a situation typical of the "Tragedy of the Commons". Indeed, encouraged by the increase in income made possible by secure access to water and faced with the degradation of services in public irrigation schemes, farmers have drilled a number of boreholes, often illegally, leading to a significant lowering of the water table. This paper analyses the determinants of this evolution, based on the comparison of two farm typologies carried out in 2005 and 2016. It also studies the impacts of different water management scenarios using a mathematical programming model representing the same farm typical of the region, in three situations of access to water (collective perimeter, private borehole, and both modes of access). The results show that the overall water demand cannot be managed with a single economic instrument and that the level of energy or water prices must be considered in relation to all local water resources and their respective costs, as well as the context of agricultural prices.