Impact of Rainfall Variability and Land Use Change on River Discharge in South Cameroon

Round 1

Reviewer 1 Report

See attached.

Comments for author File: Comments.pdf

Author Response

Cover Letter

 

Manuscript ID: water-1594936

Type: Article

Title: Impact of rainfall variability and land use change on river discharge in South Cameroon

Authors: Valentin Brice Ebodé, Jean Jacques Braun, Bernadette Nka Nnomo, Gil Mahé, Elias Nkiaka and Jean Riotte

 

Reviewers of the article water-1594936 acknowledged the important work that has been done by the authors, however, comments have been made to improve it considerably. This cover letter details all the changes that have been made to the new document.

Reviewer 1 requested a reduction of the number of authors of this work. He also requested that authors make efforts to cite their work less often. From 12 in the previous version of this article, the number of authors has been reduced to 6 in this version of the paper. We unanimously selected only authors who met all the 4 criteria to be considered as authors of an article proposed to us by reviewer 1. New analyzes relating to the explanatory factors of rainfall in the region studied have also been added to this article to consolidate it more. Concerning our review of the literature, we have made substantial effort to not cite our studies and add those of other authors.

Reviewer 1 asked to make some figures more readable. It has been done. Some figures have been divided into several, in others, the size of the writings has been increased.

Several other changes have been made in this work. The acronyms have been spelt out as proposed by reviewer 1. The equations have been correctly typeset as requested by the Two reviewers. The links of the database have been referenced in the References section as proposed by the two reviewers.

Reviewer 2 asked if the measurements after the record break in recording are homogeneous and rating curve were updated. This has been verified. The Nyong basin is the only one for which data come from two sources. But the measurement point and the process used to calculate the discharges remain the same. On the other basins, the flows have been collected since the beginning of the series by the same institution (Hydrological Research Center), and the calculation of the discharges is done using the same process.

Reviewer 2 asked if the results of the statistical analysis could be summarized in a table. He also has a concern about the clarity of the application of statistical tests concerning time series and missing data. He, therefore, proposed the use of the Mann-Kendall test. In this study, the test used for the analysis of the different series of hydropluviometric data is the Pettitt test, at the 95% confidence interval. The results are shown in Table 1. Pettitt's test was used in this study because it is suitable for incomplete series like ours. When there is a break in a series, even incomplete, the test can identify it with precision. It, therefore, has an advantage compared to other similar tests such as Hubert's Segmentation, which sometimes tends to identify false breaks when the series is incomplete. The Pettitt test was chosen to the detriment of the well known Mann-Kendall test because, in addition to indicating the direction of the evolution of the series (increase, decrease or absence of trend) as does the Mann-Kendall test, it also indicates a date from which the change observed in the series becomes significant (rupture), which makes it possible to go a little further in the analysis of variability, by comparing, for example, the parameters observed before the rupture and those observed after. We have attempted to provide some of these details in the "Data Analysis" sub-section.

Author Response File: Author Response.docx

Reviewer 2 Report

This manuscript investigated the effect of rainfall variability and land use changes on river flows in South Cameroon. The topic is of paramount importance for potential applications to be implemented in the areas covered by this study. I found the paper very rich in details and well structured. However, to my opinion the paper needs substantially improvements, which are mainly concentrated in the methodological section, that are of major importance.

 

General comments:

• Abstract: to my opinion, is really too long and needs to provide to readers only main elements of the study
• Data sources: have you checked if measurements after the break in recording are homogeneous and rating curve were updated?
• Results of statistical analysis (e.g., p-value) could be summarized in a table? It is not clear the application of statistical tests with respect to time series and missing data…could you provide a full description?
• For those series (or part of these) where you have a continuous record, why do not apply Mann-Kendall test? It would be interesting to see results.
• When you apply statistical tests (as Pettitt or Mann-Kendall) you should take into account (or, at least, mention) the need of evaluating the power of these tests. There is lot of literature on this argument, in particular focused on Mann-Kendall test. As an example, the most famous paper on this topic is that of Yue et al. (2002), while among the most recent works there are those of Wang et al. (2020) and Totaro et al. (2020). A practical implication about the use of the power can instead be found in Németh et al. (2020), while a wide discussion of statistical importance of power is in Vogel et al. (2013) and Serinaldi et al. (2018).
• Results description has, in my opinion, too many sub-paragraphs, which strongly affect the readability of this section

 

Specific comments:

 

• Lines 155-156: maybe this link can be provided in the Reference section
• Lines 180-188: Please, use a proper format for variables and equations
• Figure 2: please, add a clear legend for all lines

Author Response

Cover Letter

 

Manuscript ID: water-1594936

Type: Article

Title: Impact of rainfall variability and land use change on river discharge in South Cameroon

Authors: Valentin Brice Ebodé, Jean Jacques Braun, Bernadette Nka Nnomo, Gil Mahé, Elias Nkiaka and Jean Riotte

 

Reviewers of the article water-1594936 acknowledged the important work that has been done by the authors, however, comments have been made to improve it considerably. This cover letter details all the changes that have been made to the new document.

Reviewer 1 requested a reduction of the number of authors of this work. He also requested that authors make efforts to cite their work less often. From 12 in the previous version of this article, the number of authors has been reduced to 6 in this version of the paper. We unanimously selected only authors who met all the 4 criteria to be considered as authors of an article proposed to us by reviewer 1. New analyzes relating to the explanatory factors of rainfall in the region studied have also been added to this article to consolidate it more. Concerning our review of the literature, we have made substantial effort to not cite our studies and add those of other authors.

Reviewer 1 asked to make some figures more readable. It has been done. Some figures have been divided into several, in others, the size of the writings has been increased.

Several other changes have been made in this work. The acronyms have been spelt out as proposed by reviewer 1. The equations have been correctly typeset as requested by the Two reviewers. The links of the database have been referenced in the References section as proposed by the two reviewers.

Reviewer 2 asked if the measurements after the record break in recording are homogeneous and rating curve were updated. This has been verified. The Nyong basin is the only one for which data come from two sources. But the measurement point and the process used to calculate the discharges remain the same. On the other basins, the flows have been collected since the beginning of the series by the same institution (Hydrological Research Center), and the calculation of the discharges is done using the same process.

Reviewer 2 asked if the results of the statistical analysis could be summarized in a table. He also has a concern about the clarity of the application of statistical tests concerning time series and missing data. He, therefore, proposed the use of the Mann-Kendall test. In this study, the test used for the analysis of the different series of hydropluviometric data is the Pettitt test, at the 95% confidence interval. The results are shown in Table 1. Pettitt's test was used in this study because it is suitable for incomplete series like ours. When there is a break in a series, even incomplete, the test can identify it with precision. It, therefore, has an advantage compared to other similar tests such as Hubert's Segmentation, which sometimes tends to identify false breaks when the series is incomplete. The Pettitt test was chosen to the detriment of the well known Mann-Kendall test because, in addition to indicating the direction of the evolution of the series (increase, decrease or absence of trend) as does the Mann-Kendall test, it also indicates a date from which the change observed in the series becomes significant (rupture), which makes it possible to go a little further in the analysis of variability, by comparing, for example, the parameters observed before the rupture and those observed after. We have attempted to provide some of these details in the "Data Analysis" sub-section.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

See attached.

Comments for author File: Comments.pdf

Author Response

Cover Letter

 

Manuscript ID: water-1594936

Type: Article

Title: Impact of rainfall variability and land use change on river discharge in South Cameroon

Authors: Valentin Brice Ebodé, Jean Jacques Braun, Bernadette Nka Nnomo, Gil Mahé, Elvis Nkiaka and Jean Riotte

 

After the first corrections, some issues raised during the first review have not been fully resolved. This cover letter details all the changes that have been made to the new document.

The number of articles in which the name of one of the authors appears has been reduced as requested by reviewer 1. Several other references have also been added to the work.

Reviewer 2 requested that we present the results of the Mann-Kendall test. It has been done.

However, we were unable to include in the legend all the lines that appear in Figure 3, as requested by Reviewer 2, due to lack of space. The explanations relating to some elements of this figure appear following its title (line 343).

Author Response File: Author Response.docx

Reviewer 2 Report

Dear Authors

I read carefully your reply and the revised version of the manuscript and, in my opinion, there are some questions that have not been addressed. Here I report questions of my review to which I would appreciate a detailed reply:

 

• For those series (or part of these) where you have a continuous record, why do not apply Mann-Kendall test? It would be interesting to see results.
• When you apply statistical tests (as Pettitt or Mann-Kendall) you should take into account (or, at least, mention) the need of evaluating the power of these tests. There is lot of literature on this argument, in particular focused on Mann-Kendall test. As an example, the most famous paper on this topic is that of Yue et al. (2002), while among the most recent works there are those of Wang et al. (2020) and Totaro et al. (2020). A practical implication about the use of the power can instead be found in Németh et al. (2020), while a wide discussion of statistical importance of power is in Vogel et al. (2013) and Serinaldi et al. (2018).
• Results description has, in my opinion, too many sub-paragraphs, which strongly affect the readability of this section

 

• Figure 2: please, add a clear legend for all lines/plots

 

 

Kind regards

 

Author Response

Cover Letter

 

Manuscript ID: water-1594936

Type: Article

Title: Impact of rainfall variability and land use change on river discharge in South Cameroon

Authors: Valentin Brice Ebodé, Jean Jacques Braun, Bernadette Nka Nnomo, Gil Mahé, Elvis Nkiaka and Jean Riotte

 

After the first corrections, some issues raised during the first review have not been fully resolved. This cover letter details all the changes that have been made to the new document.

The number of articles in which the name of one of the authors appears has been reduced as requested by reviewer 1. Several other references have also been added to the work.

Reviewer 2 requested that we present the results of the Mann-Kendall test. It has been done.

However, we were unable to include in the legend all the lines that appear in Figure 3, as requested by Reviewer 2, due to lack of space. The explanations relating to some elements of this figure appear following its title (line 343).

Round 3

Reviewer 2 Report

Dear Authors

thank you for providing a reply to my comments. I still found no reply about the power of statistical tests (now also the Mann-Kendall test) and the structure of the Results section. Here I propose again the two points:

 

• When you apply statistical tests (as Pettitt or Mann-Kendall) you should take into account (or, at least, mention) the need of evaluating the power of these tests. There is lot of literature on this argument, in particular focused on Mann-Kendall test. As an example, the most famous paper on this topic is that of Yue et al. (2002), while among the most recent works there are those of Wang et al. (2020) and Totaro et al. (2020). A practical implication about the use of the power can instead be found in Németh et al. (2020), while a wide discussion of statistical importance of power is in Vogel et al. (2013) and Serinaldi et al. (2018).
• Results description has, in my opinion, too many sub-paragraphs, which strongly affect the readability of this section

 

Furthermore, I suggest to check the description of the Mann-Kendall test. You say: “The Mann-Kendall test was used to confirm the results obtained from the Pettitt test”. Could you provide references to this statement?

 

Kind regards

Author Response

Cover Letter

 

Manuscript ID: water-1594936

Type: Article

Title: Impact of rainfall variability and land use change on river discharge in South Cameroon

Authors: Valentin Brice Ebodé, Jean Jacques Braun, Bernadette Nka Nnomo, Gil Mahé, Elvis Nkiaka and Jean Riotte

 

After the second correction, some issues raised during the second review have not been fully resolved. This cover letter details all the changes that have been made to the new document.

Author Response File: Author Response.pdf

Round 4

Reviewer 2 Report

Dear Authors

thank you for the reply. In my opinion, all my suggestions have been included into the paper. However, I suggest to provide a number to all equations and define the variable "theta" in the Mann-Kendall test

 

Kind regards