Geostatistical Resampling of LiDAR-Derived DEM in Wide Resolution Range for Modelling in SWAT: A Case Study of Zgłowiączka River (Poland)

Round 1

Reviewer 1 Report

The manuscript presents an analysis of different DEM resolutions, in order to model watersheds, which falls within the scope of the Journal. Is a very important and interesting investigation, however, major revisions are required. Some examples of the revisions are listed below:

(1) Title – please simplify the title. For instance, "for modelling of low relief agricultural watershed in SWAT" should be removed because this is not the focus of the paper

(2) The manuscript should be revised by an English native. The text should also be improved in terms of scientific language

(3) Throughout the text – replace lidar with LiDAR.

(4) Introduction – very difficult to read.

(5) Material and methods – line 102 – 2750-3000ºC?

(6) Material and methods – it should be interesting to include the drainage network in the figures presented.

(7) Results – too many figures and little text

(8) line 191 - 3.1 DEM precision – this sub-chapter is more methodology. Repeated equation.

(9) line 210 - 3.2 Precision of delineation of the watershed boundaries - little content and lots of unnecessary figures. Should be interesting to have a more complete explanation of the results.

(10) Figure 4, Figure 6, Figure 12 and Figure 13 – I suggest changing to tables 

(11) Discussion – quite confusing and focused only on other studies, without a clear comparison between the results obtained. Taking into account the title of the manuscript, it would be expected that the different DEM resolutions would be applied in the SWAT model, and the impacts on the results (eg flows) analyzed taking into account the different resolutions and different cross-sections in the hydrographic network.

Others:

Correct page numeration

Figures – use the same font source as required in this journal and improve quality

Author Response

Dear Reviewer, all answers for comments were prepared in the attached table.

Author Response File: Author Response.docx

Reviewer 2 Report

In this study, the authors processed the LiDAR-derived DEM using the geostatistical sampling methods, and analyzed the potential influences of data resolution and accuracy on the derived topographic and hydrologic attributes. Overall, this research has some distinctive aspects and generate some interesting results. However, the current version of manuscript was poorly organized.

 

1. The authors should give more information about the main contributions of the work.
2. Materials and Methods. In Section 2.1, the descriptions about the statistical aggregation methods were too simple. A schematic diagram for them was suggested to provide.
3. In Section 2.2, the illustrations about the referential values and the derived DEM were not clear. Moreover, the calculation of RMSE was repeatedly defined in Equation (1) and in Section 3.1.
4. Why did the authors choose the 11 pixel sizes defined in Section 3.1?
5. The evaluation results were discussed in Section 3.1 (line 201-209). However, the quantitative results were not specified.
6. Similar problems existed in the following parts. The results need to be reorganized and analyzed accordingly. For example, the first and second paragraph in Section 3.2 seem to be not related. Where should the author infer to the specific values in the figures and tables related to the analysis (e.g., Line 233-244)?
7. The contents presented in Fig. 7—9 seem to be difficult to understand. Please give more accurate descriptions, rather than unclear abbreviations, for the figures.
8. The authors should examine over all the figures and tables, and ensure the required information are provided. What did the horizontal and vertical axis mean in Figs. 10-11? Besides, some Polish words appeared in Fig. 11.
9. Line 362, ‘in this paper, statistical sampling methods were proposed’. Did the authors propose the statistical sampling methods?
10. In the legend of Fig. 17, the style of references seems incorrect.
11. The discussion is too lengthy. The authors should more some results to the Result, and delete some insignificant discussions.
12. The language need to be improved.

Author Response

Dear Reviewer, all answers for comments were prepared in the attached table.

Author Response File: Author Response.docx

Reviewer 3 Report

line 102 - sum of temperatures ≥ 10° within 2750-3000 °C - I am not meteorologist, but I do not understend this number. Is it posible to explain?

line 247 and next - min : MIN, med :MED, ....

line 251 and next - method nir is not described in previous test (Is it NN method?)

figure 11 has title in Polish

figure 19 and next text - differences between areas [m] - is it differences between boundaries of areas? It is maximum or average differences. It is necessary more explain.

 

Author Response

Dear Reviewer, all answers for comments were prepared in the attached table.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors have improved the manuscript, which is now ready to be accepted for publication.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

The paper has presented interesting observations on varying DEM resolution and its impacts on: (a) lengths of rivers; (b) gradients of watercourses, and (c) boundary of watersheds. 

1. The influence of DEM pixel size on the derivation of terrain and hydrologic parameters can be theoretically hypothesized. For that reason, can the study clearly state the objectives of the current study over and above the obvious. 
2.  The statistical aggregation uses and compares results from nearest neighbour (NN), average (AVE), median (MED), mode (MOD), minimum (MIN), maximum (MAX). Why the simple linear interpolators? Are these likely to bring errors in the pixel size aggregation process?
3. Page 5- line 178-179: The study should present concise mathematical model that informs the degree of aggregation of the DEM resolutions.
4. Overall presentation of the results should be well structured. For example in Section 3.1, the DEM precision results are on synoptically presented and not well structured. Hence blurring the information. Further, why is Figure 8 included in the study? Figure 9 is not discussed and for the results in Table 1, Haile and Rientjes (2005) was a different case study, why compare? 
5. This study is site specific in terms of the terrain characteristics and size of rivers. Comparing the results with other case studies implies you have to take into consideration the similarities and differences with your case study.
6. Conclusions of the study sound more towards Discussions. Revise to reflect the "actual take home results from your study". And how significant are the findings in practice?
7. The manuscript is very difficult to comprehend and should be overhauled in terms of grammatical presentation.

Author Response

Thank you very much for your useful comments on our manuscript, and for giving us the chance to revise it. We have carefully reviewed each comment and made revisions accordingly. The response to each comment is given in table.

Author Response File: Author Response.pdf

Reviewer 2 Report

The article is of only relative interest. From my perspective, their results are excessively dependent on the specific physical conditions of the area studied, so that we can hardly accept their conclusions as useful on a global scale, since local conditions make it difficult to assess the importance of changes in the resolutions or pixel size of the DEMs.

The authors propose a particular evaluation, that is, on a single concrete case such as the specific watershed they study -with different resampling methods and pixel size- and their results, contrasted with those that have been appearing in the literature, only partially coincide with some, while with others they work in a completely different way. In the face of these differences, however, they do not provide a clear and convincing explanation of what is going on. From my perspective, all the works presented are deeply determined by the specific local conditions of each studied area, which makes me suspect that none of them gives a clear and convincing answer as to which resampling method and pixel size is suitable for analysing a DEM in hydrological analyses. The reader, on the other hand, in reading the work, finds himself trapped by a text in which multiple results are contrasted but from places he does not know - because he has not read all the references - and hardly obtains a clear conclusion on the problem.

The way in which a study like this is presented does not help to clearly understand the results and obtain conclusions with general validity. Different parameters are evaluated - the accuracy of the DEM, the watershed size, watercourses - and each of them is compared with other results obtained by other authors in other places of which we do not know their morphology, sometimes the size of pixels and the forms of resampling that sometimes follow methodologies associated with a software (ANUDEM, ...). Perhaps a table summarising some of these characteristics would help to understand the results as a whole and the logic behind them.

It would also have been really interesting if the analysis of the study itself had not been restricted to a single drainage basin. Perhaps the comparison with other geomorphological environments could facilitate the understanding of the differences in the results.

On the other hand, there is also a lack of a more detailed analysis or description of what is considered as ground truth and an assessment of its quality (original scale of the document, established reliability, method of collection, ...).

For all that I have said, I understand that the work can hardly be accepted for publication in a journal such as RS as its contribution is, at best, partial to a topic that is undoubtedly of interest, but as it is proposed, it is confusing and without clear conclusions.

Author Response

Thank you very much for your useful comments on our manuscript, and for giving us the chance to revise it. We have carefully reviewed each comment and made revisions accordingly. The response to each comment is given in table.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The changes introduced in the new version do not address many of the weaknesses that, from my perspective, were apparent in the first version. I understand that the article is a particular case study that may be of interest at a local level but much less so for a global publication. I therefore stand by my previous assessment.

Author Response

Thank you very much for your useful comments on our manuscript, and for giving us the chance to revise it. We have carefully reviewed each comment and made revisions accordingly. The response to each comment is given below. In the main document, we have marked the revised text in red.

Author Response File: Author Response.docx