Farm-level water-energy-food nexus optimisation using hybrid metaheuristic–mathematical programming

Irrigation decision-making is a complex, multidimensional challenge requiring integrated water and energy management to maximise farm profitability. Existing agricultural decision-making frameworks fail to optimise farm-level interactions between water and energy management in food production because simplifying assumptions are made to model crop-water interactions, resulting in researchers being unable to model deficit irrigation at the farm level. This research develops a farm-level water-energy-food (WEF) nexus optimisation framework incorporating a more detailed presentation of the soil-plant-atmosphere continuum to more realistically estimate irrigators’ response to policies affecting the WEF nexus at the farm level. The framework uses Differential Evolution to evolve AquaCrop irrigation schedules in a farm-level mathematical programming model to optimality, using the programming model’s objective function value to assess the irrigation schedules’ fitness in optimising farm-level water and energy management. The developed framework is applied to evaluate the impact of water charging methods (i.e., area-based and volumetric) and water availability on the profitability of a representative field crop farm in the Vanderkloof Water User Association command area. The results showed realistic trade-offs between irrigated area expansion (extensive margin) and deficit irrigation (intensive margin) within farm-level constraints, given the incentives created by the water charging methods. Volumetric water charges encourage efficient water use, prompting irrigators to adopt deficit irrigation to maximise profits within water quotas. Irrigators will require decision support to reconcile conventional irrigation practices satisfying crop water requirements with deficit irrigation strategies to maximise profit. The overall conclusion is that the flexibility of the optimisation framework provides a means to solve complex bio-economic models with complicated farm-level interactions and constraints.