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The analytical backbone of OPTAIN is formed by process-based predictive models operating at both field and catchment scale.
Predictive Modelling Framework
Models such as SWAT+ (Soil and Water Assessment Tool Plus) and SWAP (Soil–Water–Atmosphere–Plant model)are applied to simulate:
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Water balance components (surface runoff, infiltration, evapotranspiration, groundwater recharge)
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Nutrient transport dynamics (primarily nitrogen and phosphorus fluxes)
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Crop production responses under varying management conditions
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Effects of climate variability and projected climate scenarios
Field-scale simulations capture detailed soil–water–plant interactions, while catchment-scale simulations integrate spatial heterogeneity and hydrological connectivity. This hierarchical modelling structure ensures that field-level decisions can be translated into catchment-scale performance indicators.
The models are calibrated and validated using available hydrological and nutrient datasets, ensuring internal consistency within each case study environment.
Multi-Objective Optimisation Framework
The optimisation component builds upon model outputs by exploring combinations and spatial allocations of NSWRM across catchments.
The optimisation protocol:
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Defines decision variables at field scale (type and location of NSWRM)
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Evaluates system performance at catchment scale
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Applies multi-objective evolutionary algorithms
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Generates Pareto fronts representing efficient trade-offs
The optimisation does not identify a single best solution. Instead, it maps the decision space and reveals how objective trade-offs evolve under different configurations.
This modelling–optimisation coupling allows systematic exploration of:
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Objective weighting sensitivity
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Spatial targeting strategies
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Climate robustness of portfolios
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Cost–performance relationships