Hyper-resolution PCR-GLOBWB: opportunities and challenges of refining model spatial resolution to 1 km over the European continent

Hoch, Jannis Michael; Sutanudjaja, Edwin H.; Wanders, Niko; van Beek, Rens; Bierkens, Marc F. P.

doi:https://doi.org/10.5194/egusphere-2022-111

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https://doi.org/10.5194/egusphere-2022-111

Preprints

07 Jun 2022

| 07 Jun 2022

Hyper-resolution PCR-GLOBWB: opportunities and challenges of refining model spatial resolution to 1 km over the European continent

Jannis Michael Hoch, Edwin H. Sutanudjaja, Niko Wanders, Rens van Beek, and Marc F. P. Bierkens

Abstract. The quest for hydrological hyper-resolution modelling is already on-going for more than a decade. While global hydrological models (GHMs) have seen a reduction in grid size, thus far they never have been consistently applied at hyper-resolution (<= 1km) at the large scale. Here, we present the first application of the GHM PCR-GLOBWB at 1 km over Europe. We thoroughly evaluated simulated discharge, evaporation, soil moisture, and terrestrial water storage anomalies, and subsequently compared results with the ‘established’ 10 km and 50 km resolutions of PCR-GLOBWB. Subsequently, we could assess the added value of this first hyper-resolution version of PCR-GLOBWB as well as understand model and data requirements for future improvements.

We found that for most variables epistemic uncertainty is still large. Merely for simulated discharge we can confidently state that model output at hyper-resolution improves over coarser resolutions. This first large-scale hyper-resolution modelling attempt shows that applying a GHM consistently is by now feasible with improved data availability and computer power. Also, simulated discharge improves due to better representation of the river network at 1 km. However, currently available observations are not yet widely available at hyper-resolution or lack sufficiently long timeseries, which makes it difficult to assess the performance of the model for other variables at hyper resolution. At the model side, hyper-resolution applications require improved parameterization and implementation of physical processes to be able to resemble the dynamics and spatial heterogeneity at 1 km.

With this first application of PCR-GLOBWB at 1 km, we contribute to meeting the ‘grand challenge’ of hyper-resolution modelling. As such, it should be seen as a modest milestone on a longer journey towards locally relevant model output which requires a community effort from both model developers and data providers.

Received: 28 Mar 2022 – Discussion started: 07 Jun 2022

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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

Journal article(s) based on this preprint

31 Mar 2023

Hyper-resolution PCR-GLOBWB: opportunities and challenges from refining model spatial resolution to 1 km over the European continent

Jannis M. Hoch, Edwin H. Sutanudjaja, Niko Wanders, Rens L. P. H. van Beek, and Marc F. P. Bierkens

Hydrol. Earth Syst. Sci., 27, 1383–1401, https://doi.org/10.5194/hess-27-1383-2023,https://doi.org/10.5194/hess-27-1383-2023, 2023

Short summary

Jannis Michael Hoch et al.

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2022-111', Anonymous Referee #1, 10 Jul 2022
Review of Hoch et al. (2022) ‘Hyper-resolution PCR-GLOBWB: opportunities and challenges of refining model spatial resolution to 1 km over the European continent’

This manuscript aims to evaluate the 1 km PCR-GLOBWB model along with the challenges and opportunities associated with running the model at such finer scales. Further, the study also tests the effect of the spatial resolution of forcing datasets on model simulations. Overall, the manuscript is well written and fits within the scope of the journal.

I am not well acquainted with global hydrological modelling and some questions come to my mind automatically on reading the manuscript. The authors are requested to include answers (from their own perspective and based on what is available in the literature) to these questions in the introduction/discussion sections of the manuscript for improved understanding of readers like me.

What spatial extent constitutes a global hydrological model? Is the continental scale as given in the present study can be treated global? This question arises because of the statement that few studies have attempted hyper-resolution modelling over CONUS, but they do not have global coverage. In a strict sense, why can’t this study be termed as a continental scale application?

The major issue in hyper-resolution modelling is modelling the physical processes happening at smaller scales. When developing a hyper-resolution model over large spatial extent, the physical processes to be considered would vary from region to region. How to account for the spatial variation in physical processes in the model? Can a generic model be applied over the entire continent/globe without accounting for region specific physical processes? Or how to develop model which can consider automatically, the various hydrological processes appropriate for a region within the model domain?

One reason that is often mentioned as an advantage of hyper-resolution modelling is the ability to simulate hydrological processes over data scarce regions. If data scarcity prevents us from developing a detailed model over a particular catchment, then how can be confident about the processes simulated by a global model over such data scarce regions? Further, in hydrology, studies are there to demonstrate the transfer the information obtained over a data-rich region to a data scarce region with similar characteristics. How global hyper-resolution modelling will add value to the existing methods in understanding the processes over data scarce regions?

On a similar note, is it possible to develop a nested model structure that is followed in numerical weather modelling? i.e., develop coarse resolution model over large region and the outputs of this would act as boundary conditions of a nested model over a smaller spatial extent but at a much finer spatial resolution.

Can the authors throw some light on the improvements to be made on the numerical aspect of the models? i.e., how to improve the efficiency of the models through novel and recent numerical schemes? This might save time during model runs.

Why can’t the 1K model be validated on a grid-by-grid basis using the available high quality in situ observations even for a smaller time period? For example, soil moisture and ET can be validated using in-situ datasets. Further, for soil moisture, comparison can be made against SMAP data that are available at relatively higher spatial resolutions than the ESA-CCI data? Similarly, for ET too, comparison can be made against available high-resolution products such as MODIS 16 ET, PML-V2 product (Zhang et al., 2019) etc. This can be useful to test if the model is really performing in a hyper-resolution manner. At present, I feel the model evaluation is not rigorous enough.

References:

Zhang et al. (2019) Coupled estimation of 500m and 8-day resolution global evapotranspiration and gross primary production in 2002–2017, Remote Sensing of Environment, 222, 165–182.
Citation: https://doi.org/10.5194/egusphere-2022-111-RC1
- AC1:
  'Reply on RC1', Jannis Hoch, 24 Jul 2022
  
  Dear Reviewer,
  Many thanks for taking the time and reviewing the submitted manuscript. We also thank you for your kind words, and even more so your critical yet constructive evaluation. Please find our reaction in the attached file.
  
  Citation: https://doi.org/10.5194/egusphere-2022-111-AC1
  - EC2: 'Reply on AC1', Narendra Das, 23 Oct 2022
    
    Dear Authors:
    Please respond to the comment given by Reviewer-2.
    Thanks!
    
    Citation: https://doi.org/10.5194/egusphere-2022-111-EC2
RC2:
'Comment on egusphere-2022-111', Anonymous Referee #2, 27 Sep 2022

Hoch et al. present a study on hyper-resolution hydrologic modeling at the continental scale assessing the quality of the simulation results for varying resolution from 1 to 50km. The rational is to apply the same model at different spatial resolution with varying resolution of forcing in order to assess the added value of hyper-resolution modeling on the representation of states and fluxes at the continental scale. Observations of stream discharge, soil moisture, evapotranspiration and terrestrial water storage are used in the assessment. The results are sobering (in the way they are presented and discussed): only stream discharge simulations are improved at hyper-resolution and the authors unfortunately provided relatively little discussion on the potential reasons. Is hyper-resolution modeling dead before it really started?

In a way, the study has a conceptual problem, because upscaling and re-classification of soil texture and land cover (and water management/reservoirs?) was used to go from fine to coarse resolution. Thus the models are different not only in terms of spatial resolution and atmospheric forcing but also in terms of structure (i.e. different models at different resolution). Thus, comparability is not necessarily guaranteed, as claimed in the methods section. That’s OK, but needs to be made transparent to the reader and discussed in detail. Perhaps it’s one of the reasons why resolution does not do the trick in case of soil moisture and evaporation.

The introduction is prominently missing a discussion of the recent relevant paper by Condon et al. (2022) on global (hpyer-resolution) groundwater modeling.

2, 39: This statement is misleading. PFCONUS is just a naming convention (just as naming the setup of PCR-GLOBW over Europe PGEU). Of course ParFlow can be applied at the global scale, in principle; it’s a generic simulation tool like many others.

4, 5: Here, additional information is required in the main text. From the appendix it follows that upscaling was used for soil texture and special classification for land cover was used to move from high to low resolution (how are reservoirs upscaled/downscaled?). Thus, the models are not identical in addition to the resolution of the forcing.

Figure 3: remove 50k_50k from plot.

Why not applying the relative KGE to all variables (also soil moisture, ET)

Figure 6: Replace “other“ with correct information. Plot 1:1 line correctly everywhere. The plot almost suggests the 50k_50k is also doing better than 1k.

A couple of questions for the discussion and conclusions: Perhaps the observation data is not scale commensurate and can not be used to assess hyper-resolution modeling results? Perhaps PCR-GLOBWB is not scale commensurate and can not be used at hyper-resolution?

Language and grammar need to be revised carefully.

Citation: https://doi.org/10.5194/egusphere-2022-111-RC2
- EC1: 'Reply on RC2', Narendra Das, 02 Oct 2022
  
  Dear Authors:
  Please responsd to the comments given by the second reviewers.
  Thanks,
  Narendra
  
  Citation: https://doi.org/10.5194/egusphere-2022-111-EC1
- AC2: 'Reply on RC2', Jannis Hoch, 23 Oct 2022
  
  Dear reviewer #2,
  apologies for the respons only now but I have been on annual leave.
  Please find attached the reply to your valuable comments, on behalf of all co-authors.
  
  Citation: https://doi.org/10.5194/egusphere-2022-111-AC2

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2022-111', Anonymous Referee #1, 10 Jul 2022
Review of Hoch et al. (2022) ‘Hyper-resolution PCR-GLOBWB: opportunities and challenges of refining model spatial resolution to 1 km over the European continent’

This manuscript aims to evaluate the 1 km PCR-GLOBWB model along with the challenges and opportunities associated with running the model at such finer scales. Further, the study also tests the effect of the spatial resolution of forcing datasets on model simulations. Overall, the manuscript is well written and fits within the scope of the journal.

I am not well acquainted with global hydrological modelling and some questions come to my mind automatically on reading the manuscript. The authors are requested to include answers (from their own perspective and based on what is available in the literature) to these questions in the introduction/discussion sections of the manuscript for improved understanding of readers like me.

What spatial extent constitutes a global hydrological model? Is the continental scale as given in the present study can be treated global? This question arises because of the statement that few studies have attempted hyper-resolution modelling over CONUS, but they do not have global coverage. In a strict sense, why can’t this study be termed as a continental scale application?

The major issue in hyper-resolution modelling is modelling the physical processes happening at smaller scales. When developing a hyper-resolution model over large spatial extent, the physical processes to be considered would vary from region to region. How to account for the spatial variation in physical processes in the model? Can a generic model be applied over the entire continent/globe without accounting for region specific physical processes? Or how to develop model which can consider automatically, the various hydrological processes appropriate for a region within the model domain?

One reason that is often mentioned as an advantage of hyper-resolution modelling is the ability to simulate hydrological processes over data scarce regions. If data scarcity prevents us from developing a detailed model over a particular catchment, then how can be confident about the processes simulated by a global model over such data scarce regions? Further, in hydrology, studies are there to demonstrate the transfer the information obtained over a data-rich region to a data scarce region with similar characteristics. How global hyper-resolution modelling will add value to the existing methods in understanding the processes over data scarce regions?

On a similar note, is it possible to develop a nested model structure that is followed in numerical weather modelling? i.e., develop coarse resolution model over large region and the outputs of this would act as boundary conditions of a nested model over a smaller spatial extent but at a much finer spatial resolution.

Can the authors throw some light on the improvements to be made on the numerical aspect of the models? i.e., how to improve the efficiency of the models through novel and recent numerical schemes? This might save time during model runs.

Why can’t the 1K model be validated on a grid-by-grid basis using the available high quality in situ observations even for a smaller time period? For example, soil moisture and ET can be validated using in-situ datasets. Further, for soil moisture, comparison can be made against SMAP data that are available at relatively higher spatial resolutions than the ESA-CCI data? Similarly, for ET too, comparison can be made against available high-resolution products such as MODIS 16 ET, PML-V2 product (Zhang et al., 2019) etc. This can be useful to test if the model is really performing in a hyper-resolution manner. At present, I feel the model evaluation is not rigorous enough.

References:

Zhang et al. (2019) Coupled estimation of 500m and 8-day resolution global evapotranspiration and gross primary production in 2002–2017, Remote Sensing of Environment, 222, 165–182.
Citation: https://doi.org/10.5194/egusphere-2022-111-RC1
- AC1:
  'Reply on RC1', Jannis Hoch, 24 Jul 2022
  
  Dear Reviewer,
  Many thanks for taking the time and reviewing the submitted manuscript. We also thank you for your kind words, and even more so your critical yet constructive evaluation. Please find our reaction in the attached file.
  
  Citation: https://doi.org/10.5194/egusphere-2022-111-AC1
  - EC2: 'Reply on AC1', Narendra Das, 23 Oct 2022
    
    Dear Authors:
    Please respond to the comment given by Reviewer-2.
    Thanks!
    
    Citation: https://doi.org/10.5194/egusphere-2022-111-EC2
RC2:
'Comment on egusphere-2022-111', Anonymous Referee #2, 27 Sep 2022

Hoch et al. present a study on hyper-resolution hydrologic modeling at the continental scale assessing the quality of the simulation results for varying resolution from 1 to 50km. The rational is to apply the same model at different spatial resolution with varying resolution of forcing in order to assess the added value of hyper-resolution modeling on the representation of states and fluxes at the continental scale. Observations of stream discharge, soil moisture, evapotranspiration and terrestrial water storage are used in the assessment. The results are sobering (in the way they are presented and discussed): only stream discharge simulations are improved at hyper-resolution and the authors unfortunately provided relatively little discussion on the potential reasons. Is hyper-resolution modeling dead before it really started?

In a way, the study has a conceptual problem, because upscaling and re-classification of soil texture and land cover (and water management/reservoirs?) was used to go from fine to coarse resolution. Thus the models are different not only in terms of spatial resolution and atmospheric forcing but also in terms of structure (i.e. different models at different resolution). Thus, comparability is not necessarily guaranteed, as claimed in the methods section. That’s OK, but needs to be made transparent to the reader and discussed in detail. Perhaps it’s one of the reasons why resolution does not do the trick in case of soil moisture and evaporation.

The introduction is prominently missing a discussion of the recent relevant paper by Condon et al. (2022) on global (hpyer-resolution) groundwater modeling.

2, 39: This statement is misleading. PFCONUS is just a naming convention (just as naming the setup of PCR-GLOBW over Europe PGEU). Of course ParFlow can be applied at the global scale, in principle; it’s a generic simulation tool like many others.

4, 5: Here, additional information is required in the main text. From the appendix it follows that upscaling was used for soil texture and special classification for land cover was used to move from high to low resolution (how are reservoirs upscaled/downscaled?). Thus, the models are not identical in addition to the resolution of the forcing.

Figure 3: remove 50k_50k from plot.

Why not applying the relative KGE to all variables (also soil moisture, ET)

Figure 6: Replace “other“ with correct information. Plot 1:1 line correctly everywhere. The plot almost suggests the 50k_50k is also doing better than 1k.

A couple of questions for the discussion and conclusions: Perhaps the observation data is not scale commensurate and can not be used to assess hyper-resolution modeling results? Perhaps PCR-GLOBWB is not scale commensurate and can not be used at hyper-resolution?

Language and grammar need to be revised carefully.

Citation: https://doi.org/10.5194/egusphere-2022-111-RC2
- EC1: 'Reply on RC2', Narendra Das, 02 Oct 2022
  
  Dear Authors:
  Please responsd to the comments given by the second reviewers.
  Thanks,
  Narendra
  
  Citation: https://doi.org/10.5194/egusphere-2022-111-EC1
- AC2: 'Reply on RC2', Jannis Hoch, 23 Oct 2022
  
  Dear reviewer #2,
  apologies for the respons only now but I have been on annual leave.
  Please find attached the reply to your valuable comments, on behalf of all co-authors.
  
  Citation: https://doi.org/10.5194/egusphere-2022-111-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

ED: Reconsider after major revisions (further review by editor and referees) (08 Dec 2022) by Thom Bogaard

AR by Jannis Hoch on behalf of the Authors (23 Dec 2022) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (02 Jan 2023) by Thom Bogaard

RR by Anonymous Referee #1 (21 Jan 2023)

RR by Anonymous Referee #2 (28 Jan 2023)

Suggestions for revision or reasons for rejection

Thank you for the revised manuscript. Many of the comments have been addressed adequately. One major issue remains, which is the discussion of the results. The discussion is not useful and fails to address the potential limitations of the applied model in the application across scales. An example from the replies and the conclusions sections are symptomatic in my opinion.

In the replies the authors answer the comment on the issue of scale commensurate observations and modeling in the following way: "In our opinion, it is rather the observation data that is not (yet) scale commensurate, at least when evaluating the simulations over a longer period (>5 years). The model itself should be applicable at the 1 km scale. Nevertheless, we need to acknowledge that there is still room for improvement....". This is not an answer and actually a reason to reject the paper, since not scientific discussion is provide, only rather lapidary responses to relevant questions. In addition, in the conclusion section, the authors write for example "Our work shows that too coarse forcing resolution can eradicate benefits of model hyper-resolution." This is followed by additional general statements related to the results.

Of course there are many reasons why the model potentially is not scale commensurate. This is due to e.g. the parameterizations and parameter values, and couplings applied int the code. In addition, the results are certainly not general as implied in the conclusions section but specific to the applied model. As such they could be considered artifacts, especially if no discussion is provided on the potential limitations of the applied modeling approach. This would mean that the study does not provide any meaningful insights and should be rejected.

I strongly encourage the authors to introduce a dedicated section related to the discussion of scaling issues of observations and the applied model including a discussion of possible limitations of the applied modeling approach.

Hide

ED: Publish subject to revisions (further review by editor and referees) (08 Feb 2023) by Thom Bogaard

AR by Jannis Hoch on behalf of the Authors (10 Mar 2023) Author's response Author's tracked changes Manuscript

ED: Publish as is (14 Mar 2023) by Thom Bogaard

AR by Jannis Hoch on behalf of the Authors (14 Mar 2023) Manuscript

Journal article(s) based on this preprint

31 Mar 2023

Hyper-resolution PCR-GLOBWB: opportunities and challenges from refining model spatial resolution to 1 km over the European continent

Jannis M. Hoch, Edwin H. Sutanudjaja, Niko Wanders, Rens L. P. H. van Beek, and Marc F. P. Bierkens

Hydrol. Earth Syst. Sci., 27, 1383–1401, https://doi.org/10.5194/hess-27-1383-2023,https://doi.org/10.5194/hess-27-1383-2023, 2023

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Jannis Michael Hoch et al.

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To facilitate locally relevant simulations over large areas, global hydrological models (GHM) have developed towards ever finer spatial resolutions. After a decade on the quest for hyper-resolution (i.e. equal to or smaller than 1 km), the presented work is a first application of a GHM at 1 km resolution over Europe. This not only shows that hyper-resolution can be achieved, but also allows for a thorough evaluation of model results at unprecedented detail and the formulation of future research.


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