Making the Implicit Explicit: Documenting the Hidden Assumptions in Conceptual Models

The assumptions and simplifications captured in the conceptual model of an environmental system are a considerable source of predictive uncertainty. These choices are made in support of the project objectives, but rarely are they documented clearly and comprehensively. Although existing workflows highlight the need for clear documentation throughout the lifetime of a project, they provide little guidance on how to document assumptions and simplifications in conceptual model development. We therefore present an approach to documenting conceptual model development that increases transparency and reproducibility, which, by making the implicit explicit, allows to identify, justify, and, if necessary, correct for any biases and assumptions. We use a water table mapping case study in South Australia as an illustrative case study for systematically and explicitly documenting the conceptualisation and identifying assumptions. This allows the identification of alternative conceptualisations and data inconsistencies, and provides an a priori identification of sources of quantitative uncertainty. The benefits of documenting assumptions and simplifications are applicable to a wide range of environmental investigations.