A methodology to consider the operational constraints of collective irrigation by COupling Plants and Agents Trajectories (COPAT)

Thanks to plant growth models it is possible to generate optimal irrigation strategies at the plot scale. However, in many places irrigation is managed collectively in order to share water supply infrastructures. The purpose of the study is to evaluate the impact of collective irrigation constraints (e.g. irrigation time slots, maximum number of simultaneous irrigations, etc.) on several plant indicators. To achieve this, we propose a methodology for coupling the Optirrig model for the generation, analysis and optimization of irrigation scenarios, with the CORMAS WatASit multi-agent model which represents collective irrigated systems at the operational level. Based on the Situated Action theory and the Affordance concept, the WatASit model allows to generate the spatially distributed set of possible operations, as well as the chosen operation, for each farmer agent and for each time step during the irrigation campaign. The representation of agents irrigation strategy is then enriched by the plant indicators provided by Optirrig. In return, the agent’s irrigations impact the plants growth. We applied this methodology to a real case study of gravity-fed irrigation in Southern France. We compared the plants growth (e.g. LAI) and water stress (e.g. WSI) without collective irrigation constraints, and under two scenarios of collective irrigation management (daily slots or simultaneous irrigations). The coupling methodology required to derive a daily function of Optirrig to allow running it as a slave model on a daily basis, while crop models usually run uninterrupted from the beginning to the end of the simulation period. This daily fonction can be reused in other models, making the coupling with the CORMAS multi-agent modelling and simulation platform generic.