An optimization framework for multi-year planning of land and water allocation

Multi-year planning of allocation of agricultural land and irrigation water remains a major challenge, which is exacerbated by decreasing arable land and increasing water scarcity in many regions. This paper presents a model-based framework to address this challenge. One of the key elements of the proposed framework is that it takes into account explicitly the need to rotate crops according to some agronomically-based sequences. The framework consists of three nested optimizations: Innermost: Optimize water allocation assuming pre-divided fields and pre-determined crop rotations. Middle: Optimize crop rotation sequences within each field. Outermost: Optimize fields geometry to maximize net income. These computations leverage crop- and soil-specific 'Yield value vs. Irrigation' functions derived from an auxiliary multi-objective optimization problem, namely maximizing yield and minimizing water use. In this manner, all the planning is based on the knowledge contained in complex crop growth models (rather than simplistic models), without having to actually run these models a prohibitively high number of times. The procedure is illustrated on two 67 ha areas near Davis, CA, that altogether contained seven types of soil. Planning was performed for a 10-year planning horizon, assuming seven crops (&fallowing) and six crop rotation patterns were available to choose from. Several scenarios that differed in terms of water availability are presented. The results demonstrate the strong impact that crop rotation requirements have on the overall performance. • The main optimization procedure consists of three nested optimizations. • Simulations with crop models are required only outside of the main optimization. • The framework takes into account the need to rotate crops. • Crop rotation requirements have a very strong impact on the results. • Fallowing may be advantageous under extreme reduction of water availability.