2019/12/02 Dresden, Germany
The study of groundwater is chronically underrepresented in hydro sciences, and models – when formulated as complex as necessary and as simple as possible – prove to be useful tools for bridging science and policy in groundwater studies.
These are the main takeaways from Nexus Seminar No. 39 delivered by Prof. Marc Walther on “Numerical Modelling in Hydrogeological Sciences – Critical Evaluation or Picture-Perfect?” on 21 October 2019 at TU Dresden.
Prof. Walther began his engaging lecture with a small experiment to get the audience thinking about models. To give the substantive discussion context, he gave a background on the topic of groundwater in hydro sciences, pointing out both the main quantitative and qualitative query into the topic: water deficit and heavy metals, fracking, and salinisation, respectively.
An analysis of the thematic association of “groundwater” terms reveals the discrepancy between the perceived relevance of groundwater in academia and its relevance in reality. Much of the problem with groundwater is known but not worked on. Uneven distribution of the problem globally also calls for local assessments to be done.
To solve the challenges, Prof. Walther highlights the need for predictive tools to draw scenarios and help decision makers make better choices. Models are tools that would help bridge that gap.
In the next segment, Prof. Walther introduced the concept of modelling and identified three features of a model: illustrative/representative, reductive/simplified, pragmatic/general. He then went on to distinguish different approaches towards models – analytical, conceptual/empirical, numerical, stochastic, as well as surrogate models – and stated that the choice of model type is critical for the results and cannot be generalised or done a priori. The decision on which model to apply is case-dependent – it hinges on the circumstances and what we need from it.
While modelling may pose as a good solution, it comes with its perils. Limitations are often overlooked. The many tools involved could also decrease reproducibility for those without the appropriate background/training.
The worth of models lies, thus, in their meeting certain criteria for them to be deemed useful. According to Prof. Walther, these conditions include: how usable they are in a target region or for particular processes, resources available, how transferable and adaptable they are, and if they are robust and possible to extrapolate.
In general, Prof. Walther calls for the improvement of models. While colourful result figures are acceptable, one should provide a frame or define the colour space – explain and interpret the colours, and be clear about the boundaries of the results, highlighting limitations of projections.
To sum up, Prof. Walther relates modelling to groundwater studies, concluding that groundwater modelling is a trending topic, and should be given more visibility. Models facilitate scenario analyses and allow scientists to communicate their results to decision makers.
In the lively discussion that followed, students and fellow researchers alike raised, among others, concerns with biases – how does one account for biases in hydrogeological modelling? In response, Prof. Walther explained that there will always be unknown unknowns, and one would end up with a biased selection. What is essential is to relay that information to those who will make use of the data.
Another takeaway from the discussion was also that models are valuable not just in making science understandable but are also useful for generating interest among policymakers, for instance. Scientists are encouraged to be more confident in their work, and modellers in particular need to take the responsibility to explain.