the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 06 May 2024
Graphical representation of global water models
Abstract. Numerical models are simplified representations of the real world at a finite level of complexity. Global water models are used to simulate the global water cycle and their outputs contribute to the evaluation of important natural and societal issues, including water availability, flood risk and ecological functioning. Whilst global water modelling is an area of science that has developed over several decades, and individual model-specific descriptions exist for some models, there has to date been no attempt to visualize the ways that several models work, using a standardized visualisation framework. Here, we address this gap by presenting a set of visualizations of several global water models participating in the Inter-Sectoral Impact Model Intercomparison Project phase 2b (ISIMIP2b). The diagrams were co-produced between a graphics designer and 16 modelling teams, based on extensive discussions and pragmatic decision-making that balanced the need for accuracy and detail against the need for effective visualization. The model diagrams are based on a standardized "ideal" global water model that represents what is theoretically possible to represent in the current generation of state-of-the-art global water models participating in ISIMIP2b. Model-specific diagrams are then copies of the "ideal" model, with individual processes either included or greyed out. As well as serving an educational purpose, we envisage that the diagrams will help researchers in and outside of the global water model community to select the suitable model(s) for specific applications, stimulate a community learning process, and identify missing components to help direct future model developments.
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Status: open (until 01 Jul 2024)
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RC1: 'Comment on egusphere-2024-1303', Wouter Knoben, 13 May 2024
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Paper summary
This paper summarizes the outcomes of a large effort to create graphical representations of the inner workings of the 16 models that participated in ISIMIP2b. The result is a pair of diagrams, where the first shows in a 3-dimensional way (A) how the model discretizes the vertical domain (e.g. snow, canopy, soil, groundwater), (B) which lateral (surface) components it includes (e.g. lakes, reservoirs, wetlands), and (C) which human water use sectors are included (e.g. agriculture, livestock, industry). If a model doesn’t include a given component, that component is greyed out. The paper briefly describes the process that led to the creation of these diagrams, possible ways in which the diagrams could be used, and some thoughts about creating these diagrams for models not included in ISIMIP2b.
Review summary
I think this paper is an interesting and timely contribution, and I expect this process was anything but easy. Better understanding which models to use when, where and for what purpose is critical for actionable decision making, and these diagrams might be helpful in both conversations between model developers and model users, as well as outline experiments that would lead to such better understanding. The graphics are clean and the paper is generally easy to read. However, I think some important information is missing and I think the paper needs to be revised before it can be published.
Major comments
I have several major comments, based on my reading of the paper and multiple line-by-line comments that can be found in the attached .pdf:
1. The main methodology used in this paper seems to be that everyone involved went through a long process of deliberations about how the final diagrams should look. I'm not very familiar with how such social processes are typically documented and described in journal articles, but the current description of it in the paper is very short: there is almost nothing about the process beyond its outcomes. However, these discussions lie at the heart of the resulting diagrams and I think more description of how they were organized, which stakeholders and backgrounds were present, how different points of views and needs were balanced etc. is needed. I think the paper in particular needs more information about how the main trade-offs between accuracy/detail and aesthetics/clarity were made, and why the resulting two diagrams are seen as the right balance between these different things. Are there transcripts of the conversations that were had?
2. I have some concerns about some of the phrasing in this paper, and how that relates to the wider context of modeling capabilities as well as extensions of these diagrams. The paper is quite clear about the fact that the term for the complete diagram (i.e., the “‘ideal’ model”) is not meant to be seen as a statement that describes how the ideal Earth system model looks. I believe that if this is so, then simply using a different term is more appropriate. I’ve suggested “ISIMIP-complete” in the comments but I think anything that avoids the implicit message that this is how an ideal model looks is better than what is currently used.
This becomes particularly important in the discussion section of the paper. Here the authors discuss these ISIMIP models and the resulting “ideal” model diagram as what is currently feasible within the scientific community. The word “ideal”, in my opinion, implies much more than is justified here. The community as a whole has larger modeling capabilities than what is shown by this specific subset of models, and what can feasibly be done by the community extends beyond what this “ideal” model diagram shows. I think it is important to be honest about limitations in our models (and these diagrams do a good job of giving high-level overviews of what specific models can and cannot do), but I think it is equally important to not undersell what is currently feasible if the community were to integrate all the separate bits of expertise in a coherent way. I don’t think this is necessarily a discussion that needs to be had in this paper, but I do think it is important to acknowledge that the word “ideal” implies certain things, no matter how often the paper says that that is not the way the reader should interpret the word - particularly if these diagrams are partially meant to facilitate discussion with stakeholders who possibly don’t have much personal modeling experience or clear overviews of the current-state-of-the-art of environmental modeling. Using a different term than “ideal” completely avoids all of this.
Finally, I think the phrase “ideal” model limits the ability to extend this diagram beyond what it currently includes. The authors list multiple aspects of environmental modeling that are not included by any of the models in ISIMIP2b and thus are not included in the “ideal” diagram. What happens when a model is included that introduces a new capability? Will this lead to the “ideal v2” or “slightly more ideal” diagram? A more version-y phrase would be more extensible in such future scenarios. This would also be more in line with the GMD requirement to include specific version numbers in the titles of a number of manuscript types (I’m aware that this is not required for review and perspective papers, but that doesn’t make it a bad idea in general).
3. I think the paper could also use a bit more text on some of the more practical concern about modeling capabilities that go beyond what’s currently in the diagrams. How easy will it be to adapt the JSON tool and the diagrams themselves with new fluxes or other relevant information? Will there have to be a new design process to avoid cluttering what is currently there? Will new trade-offs between accuracy and aesthetics need to be made?
4. Something I have missed in the paper is a description about energy balance calculations. The model inputs suggest that at least some of these models try to explicitly account for energy balance components but neither the diagrams nor the text provide any information about this. Were energy-related state variables simplified away in favour of readability? If so, I think this needs to be discussed in the paper.
Minor comments
Please see the attached .pdf. There is some overlap between those comments and the major ones I outlined above.
Model code and software
Prototype for automatic model diagram generation Hannes Müller Schmied https://github.com/hmschmie/automodeldiagram
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