Mathematical models are central to systems assessment. Although, in practice, much of the work to develop them rests on system understanding and scenarios, the models still need to be defined in a rigorous way. It is essential that the models reflect the system being assessed adequately. 'Off the shelf' models might be sufficient for simple exercises, but even when they are, it is important to understand what the model is, rather than treat it as a 'black box'.
This is why Quintessa takes a structured approach to developing models. This usually starts with building a 'conceptual' model that reflects the assessment context, system understanding and scenarios. A conceptual model may be no more detailed than a diagram with boxes to represent 'features' of interest (e.g. soil, rivers, plants) and 'processes' that act between them (e.g. water flow, absorption of nutrients by plants). The next stage is to describe these mathematically. Quintessa’s experience and knowledge mean that mathematical models can be built efficiently, whether from a basis in physical science or from accepted empirical models.
Finally, the mathematical models need to be implemented in a suitable piece of software. This could be a spreadsheet or a detailed modelling tool, but should always be appropriate to the level of detail demanded by the assessment. Quintessa has a wide range of codes available, including applications like AMBER and QPAC that we have developed ourselves and have been widely used.