The Thresholds of Sediment-Generating Rainfall from Hillslope to Watershed Scales in the Loess Plateau, China

Round 1

Reviewer 1 Report

I found the topic of the study very interesting and in line with the scope of the journal. The study is well-written, scientifically conducted and the conclusions were comprehensively supported by the data. To improve the overall quality of the manuscript, I have some suggestion/comments as below:

The quality of the figures 1 may be improved, at least in my pdf they are getting a bit distorted.
Comment line 368: You could also insert the reference: Zheng, M.G., 2018. A spatially invariant sediment rating curve and its temporal change following watershed management in the Chinese Loess Plateau. Sci. Total Environ. 630, 1453–1463.
5. Conclussion. Instead of Conclussion, it should be replaced by Conclusion.
English needs to be revised.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

In my opinion, the manuscript submitted to Water titled “The thresholds of rainfall generating sediment from hillslope to small watershed scales in the Loess Plateau, China” requires at minimum major revision to be considered for publication. This manuscript analyzes field data on precipitation, runoff/erosion, and suspended sediment concentration in nested watersheds in China’s Loess Plateau region. Data acquisition began in 1990 and was active until 2016, so I believe interesting and valuable results could be coaxed out of the field data. However, there are substantial structural problems with the manuscript that currently prevent it from being a valuable contribution. I have provided detailed comments in the edited .pdf, but will also recount general issues/comments below.

First, the paper would strongly benefit by a rigorous edit for English. There are many minor grammatical issues, as well as some major issues that prevent understanding. In addition, there are some spelling errors, misused acronyms, and confusing sentences that careful editing should fix.

Second, the figures and tables need to be better. Figures 1 and 2 do a poor job of placing this study in the correct geographic and geomorphic context.

Third, there needs to be more detailed explanations of background, methods, and results. The authors appear to assume the reader has detailed knowledge about methodology, phrases, and key words that are never fully explained (if at all). It is difficult to follow what is being done, and why it might matter, without better explanations.

Fourth, the results are presented as a “list” rather than with real coherent structure. I encourage the authors to re-write the results in a more meaningful, interesting, and easy-to-follow way.

Fifth, the discussion is not detailed enough and only touches the surface of other work on these subjects. There are numerous sentences that essentially say “X could be explained by Y factors” and then cite a couple papers – that is not a true discussion and needs to be improved. Instead, say something like “author X demonstrated that Y could be a factor in slowing sediment transport from hillslope to channel in loess-rich regions, and our data suggest….” 

These issues combine to make the paper difficult to follow and make it so that I cannot figure out the novelty or importance of this work. In sum, I think the data could be used as the center of an interesting manuscript but there needs to be substantial changes to the structure and content of the manuscript.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Dear Authors/Editor:

Overall comments

The manuscript is well written. Results are based on data.

Results are interesting for a local audience or for audience in watersheds with similar characteristics.

Abstract

The objective of the paper entitled “The thresholds of rainfall generating sediment from hillslope to small watershed scales in the Loess Plateau, China” is to “… present the concept of thresholds of rainfall generating sediment” which is defined as the precipitation or intensity value that generates soil erosion.

Even that the abstract is clear in general, it introduces some concepts that are not clearly explained. Among those concepts not clearly explained are:

LINE 27. Rainfall type C LINE 26, rainfall type A LINE 24, Rainfall covering area proportion LINE 28 AND OTHERS. I Is it intensity in a period of 30 min? Is it intensity associated to percentile 30^th?

Authors should modify the abstract trying to get a piece of literature able to be understood by itself. I know that those concepts will be explained later, however keep in mind that many readers would only have access to the abstract in a first stage.

Introduction

LINE 54-62.

Erosion process does not only depend on precipitation characteristics but also on other factors as edaphology, slope or vegetation. Authors should also include these data, and not only precipitation data, for the studies they are citing in order to provide a complete information from the previous studies.  Even more, in lines 433-438 the authors stated that the results can be extrapolated to other “loess hilly areas with similar climatic conditions, soil characteristics and geomorphologic landscapes”  highlighting the importance of those other factors affecting soil erosion.

TABLE 1. All study plots have the same land use of fallow. Nevertheless, in figure 2 it can be seen a clear change in the colour of the land in some areas in the plots number 6, 7 and 8. Is it shadow or a different vegetation type?

What kind of vegetation exist in the fallow plots?

Lines 123-127

Please, provide a more extended information about the procedure to obtain sediment yield data. Sedimend gauge?  Sediment data obtained from water samples?

Sediment yield data is critical in the present study and a complete explanation should be included in the present study.

LINE 125.

What YRCC stands for?

LINE 160 and others.

 “Thiessen”. Please, correct.

LINE 200.

“The best… with the smallest…”

LINE 202.

Equation two is not correctly organized.

TABLE 3.

Results of MI and its sub-parts N_up/N_t and N_dn/N_t show that the former part is much more important than the second when computing the MI (N_up/N_t  is generally higher than ten times the N_dn/N_t).

Ideally, both parts should be in the same order of magnitude. This fact is showing that the thresholds of rainfall generating sediment should be higher than the present one. 

A more intense discussion about this fact should be included and, maybe, a new proposal for the definition of the threshold.

Later, authors have discussed about this fact in section 3.1.2, when they have stated that the N_up/N_t is much smaller when dealing with intensity threshold. However, nothing is included in section 3.1.1 devoted to precipitation threshold.

From my point of view, this fact is showing that the key characteristic for the study of soil sediment erosion is not the total amount of precipitation but the intensity.

I miss a table similar to table 3 but with the factors I30, I60, PI30 and PI60. I would like to see the N_up/N_t , N_dn/N_t and R² when using these other factors. It will show data to determine the more important factor of precipitation in soil sediment production.

I see that some the required information is in figure 4. I consider that the information should appeared in table.

Figure 4 shows again that factors considering P have the highest MI index values for all scales considered. Please include a longer discussion about this fact.

Section 3.2.1

I do not see the point of classifying the precipitations events in type A, B, and C because they have used as a criteria the intensity and total precipitation of each events and those same variables has already been considered as potential factor in the previous steps.

Results are somehow expected for this section, if precipitation events A collects those events with high intensity and low total precipitation, it is clear that the threshold obtained from this group will be higher (in intensity) and lower (precipitation) than the thresholds obtained from events in the group B.

I would ask the authors to consider the inclusion of such a classification in the manuscript. Alternatively, they should justify its inclusion in a better way.

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

I appreciate the effort of the authors to respond to my critique of their paper titled “The thresholds of rainfall generating sediment from hillslope to watershed scales in the Loess Plateau, China”. I believe that substantial progress was made, and many of my major concerns have been addressed. I particularly appreciate the improvement to Figure 1 and the discussion section.

I suggest minor revisions should still be made based on the comments I have added to the .pdf document.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.docx