Non-Stationary Flood Discharge Frequency Analysis in West Africa

Round 1

Reviewer 1 Report

In this manuscript, the authors have developed non-stationary flood frequency models of the annual maximum flows of major rivers in West Africa for future exploration of flood forecasting. The structure is well-presented. I recommend that the manuscript to be accepted for publication after making the minor correction.

1. Should have more descriptions on non-stationary in Section 1

2. Please add a summary of the novelty at the end of Section 1.

3. Is there any equations involved in 2.3 Methods? If yes, kindly present it and state the reason why the methods were selected for analyses.

4.   Line 277, if the BIC value is large, what does it mean? Please provide further elaboration.

5. Line 279, why Gumbel distribution is preferable?

 

Minor editing of English language required

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript „Non-stationary flood discharge frequency analysis in West Africa” is well prepared and it will be of interest to readers of GeoHazards Journal, as well as to experts in river basins floods and not only. However, I have some recoomendations:

Line 12 – delete the (before intensification)

Line 13 - delete the (before hydrological variables)

Line 27 – you have an extra dot

Lines 39, 45, 50, 55, 59 – you have an extra space

Maps should be more clear and separted in A and B for Fig. 1

Lines 80, 109 – you have an extra space

What is the program/soft that was used for statistics??

Line 180 – delete Table of model types

Lines 197, 198 – should be moved to Methodology

Line 206 - ‘Signifi’ – should be moved under the table

Lines 209, 211 – show – should be shows

Figure 3 should be more clear

Line 299 – you have 2 extra space

Lines 305, 314, 316 – you have an extra space

Lines 304, 305, 306 – should be moved to Introduction or delete them

You should cite more recent references related to this study

English grammar and spelling should be carefully checked

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 3 Report

line 37: „several hectares of crops washed away“: Really just a few hectares? That is not very much. Please check.

 

line 39: Please cite the reference

 

line 43: Please define to readers what is „non-stationarity“. Many readers will not be aware of this concept. What is the difference to „stationarity“?

 

line 63: A key component for West African floods and rainfall is natural variability of precipitation. This is partly linked to „modes of variability“. Please add this component to your study as you also refer to „climate change“. A key paper on this is by Lüdecke et al. 2021: https://doi.org/10.1016/j.ejrh.2021.100795 . There are also two rainy seasons along the Gulf of Guinea coast (January-March and July-September). According to Lüdecke et al. 2021 the first rainy season is affected by the North Atlantic Oscillation (NAO) and the Indian Ocean Dipole (IOD), whereas the second rainy season is influenced by the Pacific Decadal Oscialltion (PDO). Please ckeck Figure 3 of that paper. Before drawing any conclusions on floods in West Africa, these modes of variability have to be taken into account. Unfortunately, none of these important indices has been considered in this study (see chapter 2.2. of the manuscript). IOD and PDO are related to Sea Surface Temperatures (SST), whilst NAO refers to air pressure differences.

 

Line 100: Add basins to figure caption

 

Line 153: Please add more information on significance testing in this chapter

 

Line 303:

You should clearly explain why it matters whether a station is stationary or non-stationary. For most readers this has no meaning. What did the study really show?

Author Response

Please see the attachment

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

Manuscript has now been improved. Discussion of modes of variabilty is still insufficient. It is understood that PDO=ONI and NAU=TNA. But implications of Lüdecke et al. 2021 have not been included, nor the results of the paper apparently understood. It is very important to include these factors of natural climate variability in the final paper.  Comment that still needs to be included was:

"A key component for West African floods and rainfall is natural variability of precipitation. This is partly linked to „modes of variability“. Please add this component to your study as you also refer to „climate change“. A key paper on this is by Lüdecke et al. 2021: https://doi.org/10.1016/j.ejrh.2021.100795 . There are also two rainy seasons along the Gulf of Guinea coast (January-March and July-September). According to Lüdecke et al. 2021 the first rainy season is affected by the North Atlantic Oscillation (NAO) and the Indian Ocean Dipole (IOD), whereas the second rainy season is influenced by the Pacific Decadal Oscialltion (PDO). Please ckeck Figure 3 of that paper. Before drawing any conclusions on floods in West Africa, these modes of variability have to be taken into account. Unfortunately, none of these important indices has been considered in this study (see chapter 2.2. of the manuscript). IOD and PDO are related to Sea Surface Temperatures (SST), whilst NAO refers to air pressure differences."

 

Author Response

Reviewer comments

Manuscript has now been improved. Discussion of modes of variabilty is still insufficient. It is understood that PDO=ONI and NAU=TNA. But implications of Lüdecke et al. 2021 have not been included, nor the results of the paper apparently understood. It is very important to include these factors of natural climate variability in the final paper.  Comment that still needs to be included was:

"A key component for West African floods and rainfall is natural variability of precipitation. This is partly linked to „modes of variability“. Please add this component to your study as you also refer to „climate change“. A key paper on this is by Lüdecke et al. 2021: https://doi.org/10.1016/j.ejrh.2021.100795 . There are also two rainy seasons along the Gulf of Guinea coast (January-March and July-September). According to Lüdecke et al. 2021 the first rainy season is affected by the North Atlantic Oscillation (NAO) and the Indian Ocean Dipole (IOD), whereas the second rainy season is influenced by the Pacific Decadal Oscialltion (PDO). Please ckeck Figure 3 of that paper. Before drawing any conclusions on floods in West Africa, these modes of variability have to be taken into account. Unfortunately, none of these important indices has been considered in this study (see chapter 2.2. of the manuscript). IOD and PDO are related to Sea Surface Temperatures (SST), whilst NAO refers to air pressure differences."

Response:

We appreciate the reviewer's time and the comments made on our manuscript. We have read carefully the paper of Lüdecke et al. 2021. As indicated in the comments, the indexes that are recommended by the reviewer (PDO, IOD, and NAU) have been taken into account in the manuscript. The aim of the paper was not to collect all the possible climate indexes that could be correlated with the high discharge series in the analysis but to select the good covariate with significant correlation. To avoid overfitting the distributions and as the indexes are not necessarily independent, we did not judge useful of including many indexes per station.  We included however in the discussion section some implications of the paper by Lüdecke et al. 2021 on the analysis. We hope that this version will meet the reviewer's expectations.  Thank you very much.