Modeling Land Use

Agriculture is confronted to the following question: under what circumstances will humanity be able to feed its future population? The recent answers brought to this question - increase of surfaces and above all intensification of production - are showing their limits. And indeed, there is only a small margin left for the increase of both parameters. What is more, the environmental impacts produced threaten the system's sustainability. Among the environmental challenges that have to be faced, adaptation to climate changes originates major uncertainties. The setting up of a tool for economic prospective including agronomic and technical constraints thus appears to be necessary. None of the existing models which are presented briefly in this report takes into account simultaneously economic processes, production mechanisms and environmental feedbacks. We present in this report the questions raised by the representation of supply in Nexus-Land- Use, a partial equilibrium model which was designed to tackle these aspects. The rarity and the price of the available data are the main constraints to the development of such a model. Moreover, the question of the potential evolution of yields remains a major difficulty. Finally, taking into account the production process requires dealing with the question of the representation of technical itineraries, as well as that of spatial representation. The complex question of water is in this respect particularly important. Besides, an example of a technico-economic representation is presented for the case of ruminant livestock breeding, for which a simplified production function is proposed. And finally, a simplified version of the model Nexus Land-Use for Europe-15 stresses the importance of the questions just mentioned. (authors)