Articles | Volume 9, issue 5
© Author(s) 2021. This work is distributed underthe Creative Commons Attribution 4.0 License.
A hybrid data–model approach to map soil thickness in mountain hillslopes
- Final revised paper (published on 11 Oct 2021)
- Supplement to the final revised paper
- Preprint (discussion started on 18 Jan 2021)
- Supplement to the preprint
Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor |
: Report abuse
RC1: 'Comment on esurf-2020-110', Nicholas Patton, 28 Feb 2021
- AC1: 'Reply on RC1', Qina Yan, 31 Mar 2021
RC2: 'Comment on esurf-2020-110', Jon Pelletier , 01 Mar 2021
- AC2: 'Reply on RC2', Qina Yan, 31 Mar 2021
Peer review completion
AR: Author's response | RR: Referee report | ED: Editor decision
AR by Qina Yan on behalf of the Authors (31 Mar 2021)  Author's response Manuscript
ED: Referee Nomination & Report Request started (24 Apr 2021) by Cornelia Rumpel
RR by Jon Pelletier (24 Apr 2021)
ED: Reconsider after major revisions (25 Apr 2021) by Cornelia Rumpel
AR by Qina Yan on behalf of the Authors (07 Jun 2021)  Author's response Manuscript
ED: Referee Nomination & Report Request started (01 Jul 2021) by Cornelia Rumpel
RR by Jon Pelletier (27 Jul 2021)
ED: Publish subject to minor revisions (review by editor) (27 Jul 2021) by Cornelia Rumpel
AR by Qina Yan on behalf of the Authors (30 Jul 2021)  Author's response Author's tracked changes Manuscript
ED: Publish as is (31 Aug 2021) by Cornelia Rumpel
ED: Publish subject to technical corrections (31 Aug 2021) by Niels Hovius(Editor)
Review of Yan et al.
I have read the manuscript, “Hybrid data-model-based mapping of soil thickness in a mountainous watershed” by Yan and colleagues. The authors present a new approach to predicting soil thickness that utilizes the strengths of both numerical and empirical relationships within a portion of the East River, CO watershed. The new data presented here are 78 auger and 54 CPT measurements for 78 locations across two aspects. Their work produces a high-resolution (0.5 m) map of soil thickness, production rates, and transport rates for the two dominate aspects. I found this paper a pleasure to read. I thought it was interesting and provided a creative approach for predicting soil thickness where other approaches have limitations. This document is well written and has a logical flow that is easy to follow; however there are sections that could use more clarification to strengthen the approach and conclusions. Overall, the work was of good quality and falls within the scope of Earth Surface Dynamics target audience. Below I have provided a brief list of major and minor comments to the manuscript. In addition I have submitted a PDF with a more complete and thorough in-text comments.
Methods clarity- Though I generally understood how your models work, it was difficult to follow the step-by-step methods (i.e., when each variable/equation is used). Could you more explicitly describe what equations (EQ1-10) and all the necessary variables (7) that the reader would need to use in your approach? At the present, I cannot tell if you calculate your 7 variables using OAT or your model, or if they already have been determine in a past study. Please clarify. Lastly, I would recommend making a diagram in the supplementary information that highlights the workflow and points to the exact equations and variables that are mentioned within the text.
Smoothing and resampling grid size- The different methods for smoothing the landscape is interesting but it’s still unclear if it’s extremely important for your study and possibly removes the focus away from the main findings. Curvature can be calculated at any resolution but what I am gathering from Sections 2.3 and 4.1 is that the authors want the highest resolution with the lowest RMSD, hence why they selected there smoothing over time approach. To my knowledge, I have not seen any studies which smooth elevation data using diffusion equations and since the authors did not mention any previous studies, I am assuming this is new. If it is not, please provide some references. I do have some concerns with this smoothing approach:
Sensitivity analysis- I have read through Section 2.4 and Results 4.2 several times, but I am still having a difficult time wrapping my head around the 7 variables, associated uncertainties, and subsequent sensitivity. Below are my two major questions. More clarification would be greatly appreciated. Lastly, it would benefit the general audience who may not have much expertise in the OAT method (such as myself) to provide a brief explanation on how to interpret Figure 3.
Model comparison- You predict soil thickness through your hybrid approach and the random forest approach but why not compare it with the components of your model (i.e., just predicting soil thickness using the conservation of mass models and the Patton et al. method)? In the methods you nicely lay out their limitations but you could also demonstrate it. I am particularly interested in how your model will compare with the Patton et al. method because, like your model, it can determine soil thickness across the full topography. By adding a direct comparison you might be able to see additional pros and cons of the models. At the moment there are some clear benefits of your model and worth highlighting such as: you can account for the full landscape where the conservation of mass equations cannot, the Patton et al method is limited to a 5 m resolution, and your model can determine soil production and transport rates.
Model validation- I have no doubt that your hybrid approach is appropriate for other locations, given your reasonable results, but this has not been actually tested. A cross site comparison would be beneficial, specifically in sites that the Patton et al. approach is limited (watersheds with broad distributions of curvatures and avaible data) (i.e., Gordon Gulch, CO; Coos Bay, OR; Marshal Gulch, AZ). This would validate your models versatility and provide an additional comparison between the models.
Defining- Many of your symbols (i.e., Ethre) and specialized vocabulary (i.e., curvature) are missing definitions. Geomorphology is becoming increasingly interdisciplinary. Please insure you have clearly defined the words and the equations used. See PDF for in-text examples.
Figures- Overall, the figures are helpful to understand and progress the reader through the manuscript; however, minor edits will greatly benefit their readability. Please see comments in PDF for figure comments.