ABSTRACT The South African government has put legislation in place to exercise better control over irrigation water usage. Thus, proper planning of irrigation areas and scheduling of irrigation events in order to stay within water quotas has become more important. Currently, the available methodologies to assist irrigation farmers overlook the complexities and interrelated relationships between crop-area planning and the multi-stage nature of irrigation-scheduling decisions within a stochastic dynamic environment. This paper contributes to knowledge through the development of a bio-economic model that uses evolutionary algorithms to optimise water use, taking cognisance of the complex interrelationships between crop-area planning, the multistage decision-making nature of irrigation-scheduling decisions, and the stochastic dynamic environment under conditions of limited water supply. The results show that gross margin variability is reduced and the expected outcomes are improved due to improved irrigation-scheduling decisions made sequentially in multiple stages. Multi-stage decisions tend to make the impact of risk aversion less profound because taking account of unfolding weather information is risk reducing. Ignoring the risk-reducing impact of sequential decision-making will over-estimate the cost of water restrictions. Caution is hence necessary when formulating agricultural water-allocation policies based on crop water optimisation models that overlook the complex nature of irrigation decisions.

中文翻译：

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单阶段和多阶段决策框架内最佳水资源分配的风险效率

摘要 南非政府已制定立法以更好地控制灌溉用水。因此，正确规划灌溉区域和安排灌溉活动以保持在用水配额内变得更加重要。目前，帮助灌溉农民的可用方法忽略了作物面积规划与随机动态环境中灌溉调度决策的多阶段性质之间的复杂性和相互关联的关系。本文通过开发使用进化算法优化用水的生物经济模型，认识到作物面积规划之间复杂的相互关系、灌溉调度决策的多阶段决策性质、以及有限供水条件下的随机动态环境。结果表明，由于改进了在多个阶段按顺序做出的灌溉调度决策，毛利率可变性降低了，预期结果得到了改善。多阶段决策往往会使风险规避的影响不那么深刻，因为考虑到正在展开的天气信息可以降低风险。忽视顺序决策降低风险的影响将高估水资源限制的成本。因此，在根据忽略灌溉决策复杂性的作物用水优化模型制定农业用水分配政策时，必须谨慎。结果表明，由于改进了在多个阶段依次做出的灌溉调度决策，毛利率可变性降低了，预期结果也得到了改善。多阶段决策往往会使风险规避的影响不那么深刻，因为考虑到正在展开的天气信息可以降低风险。忽视顺序决策降低风险的影响将高估水资源限制的成本。因此，在根据忽略灌溉决策复杂性的作物用水优化模型制定农业用水分配政策时，必须谨慎。结果表明，由于改进了在多个阶段按顺序做出的灌溉调度决策，毛利率可变性降低了，预期结果得到了改善。多阶段决策往往会使风险规避的影响不那么深刻，因为考虑到正在展开的天气信息可以降低风险。忽视顺序决策降低风险的影响将高估水资源限制的成本。因此，在根据忽略灌溉决策复杂性的作物用水优化模型制定农业用水分配政策时，必须谨慎。忽视顺序决策降低风险的影响将高估水资源限制的成本。因此，在根据忽略灌溉决策复杂性的作物用水优化模型制定农业用水分配政策时，必须谨慎。忽视顺序决策降低风险的影响将高估水资源限制的成本。因此，在根据忽略灌溉决策复杂性的作物用水优化模型制定农业用水分配政策时，必须谨慎。