Résumé
The objective of this paper is to compare several economic instruments which may be implemented to mitigate current farmers' groundwater withdrawals in a multi-resource system. We conduct a fined-tuned field work with farmers to understand the key points of substitution between underground and surface water at the farm level. A linear programming framework has been used to model fruits and vegetables production systems. It shows that groundwater demand is sensitive to its variable cost, advocating for effectiveness of price-based instruments to mitigate underground irrigation withdrawals. Although economists often advocate for such instruments superiority, volumetric surface water pricing and fees on groundwater consumption partially fail to satisfy our five criteria for instruments assessment. We finally support the implementation of a quota system on groundwater in our case study, although a discount on the current surface water tariff could be considered. The latter could be framed by the so-called "Organisme Unique" introduced by the 2006 Water and Aquatic Environment Law.