E.T.: An operational field water and salt flows model for agricultural LCA illustrated on a Moroccan Mandarin

Objectives: Water inventory and agri-food LCA databases do not fully support the application of LCIA methods assessing the impacts of consumptive and degradative water use (so-called water availability as proposed by Boulay and colleagues), and are not appropriate for LCA-based ecodesign of cropping systems. For herbaceous crops, the FAO Aquacrop model constitutes a relevant and operational model for estimating field water and salt flows, but no dedicated model is available to-date for perennials. The objectives of this work were (i) to develop a simple and operational model for the estimation of field water and salt flows, aiming at discriminating practices for all types of cropping systems including perennials, (ii) to test and discuss its feasibility in a demanding case study. Methods: After a review of modelling approaches, we elaborated a tailored model, called the E.T. model, for the inventory of field water and salt flows for use in LCA of cropping systems. The model has a daily water and salts balance, accounting for specific soil, climate and agricultural practices. We explored the model relevance and robustness in a case study of a mandarin crop grown in Morocco, based on farm primary data. We compared the model outputs with the literature and water databases, and calculated water availability impacts. Results: The E.T. model is simple and operational on perennial crops, and estimates evaporation, transpiration, deep percolating water and runoff water, in terms of volume and salinity. Its outputs compared well with literature and measurements, and allowed the simulation of scenarios of agricultural practices. A comparison with crop water consumption estimates from databases highlighted a difference of up to 60%. E.T. model outputs are water elementary flows and salinity and can be used for assessing the impacts of consumptive and degradative water use in LCA. Conclusions: The E.T. model supports the calculation of water availability impact while discriminating agricultural practices. Its domain of validity and accuracy could be extended based on recommendations from the authors.