Modelling the Temporal Dynamics of Groundwater Pollution Risks at the African Scale

Round 1

Reviewer 1 Report

The manuscript: “Time dynamic pollution risk modelling of groundwater at the African scale”, by Ouedraogo et al. is a good example of modification of DRASTIC approach with a simple tool, specifically tailored to model risk pollution with publicly available data in a real dynamic system at the continental scale. Authors have appropriately documented used method, however, the concept of the work need to be better explained, in some details. The paper also needs minor changes before publication. Please see below.

Comments:

1. It is not usual to cite a literature reference in the abstract. Please change the second sentence in the abstract, by quoting that your method is based on dynamic hypothesis. You can easily refer to your previous work (static hypothesis) in the introduction of your manuscript.
2. Please, explain abbreviations ECOWAS, IGAD, SADC, SEDAC and SDG-6 in the introduction of manuscript.
3. Please add a missing keyword: risk modelling
4. Line 42: literature references 7 and 8 can be omitted, or better explain their significance in the context of your work.
5. Line 118: please explain exactly what type of data you have used (try to avoid expression: several data…)
6. Line 121: please write down the name of the GIS software you have used.
7. Line 147: please explain what kind of variation can be observed near the Lake Viktoria…
8. Chapter 2.2.2; lines 171-199: please explain in more details characteristics of static parameters (values) you have used in your work, with emphasis on data collection and quality issue. Do not refer only to previous work!
9. Lines 224-244: Local groundwater pollution is not in the core of this manuscript. Authors should focus on description of general trends of groundwater pollution at the continental scale.
10. Figures 6 and 7: titles of these figures are vague and non-consistent. You may consider merging these figures in one figure (Figure 6, a and b), due to better visualisation and understanding of results. Before, please explain the methodology of relative and absolute risk index variation
11. Line 256: use: to some extent instead of considerably
12. Line 258: Vague sentence, please consider to revise it.
13. Lines 261-262 – put this sentence in the section: Conclusion.
14. Figure 8 – you can delete it. It doesn’t provide any new information
15. Line 285 – add “scale” after “regional”
16. Line 287 – delete: “is” after “also for”
17. Line2 288-290 – please explain better
18. Lines 303-307 – you should refer to limitations of method, by using your own findings (your results) and then referring to the previous research. Please, be specific on this issue.
19. Please cite the literature references following “Instructions for authors” of the Water journal.

Author Response

Dear Anonymous Reviewer#1,

We thank the Reviewer for their constructive and helpful suggestions; we have provided our responses to the reviewer’ comments. We have addressed all issues indicated in the review report. We hope the Reviewer and the Editor will be satisfied with our responses to the ‘comments’ and the revisions for the original manuscript. We have highlighted (blue colour) the sections in the manuscript which have been amended or re-written.

Author Response File: Author Response.pdf

Reviewer 2 Report

This manuscript aims to assess the dynamic behaviour of groundwater pollution risk at the continental scale, using the parametric DRASTIC model. The relationships between groundwater pollution risk and time dynamic drivers of the pollution risk have been developed. The results show that the elaborated pollution risk maps has an important variations of the spatial distribution of pollution risk between the three years. I carefully read this manuscript, and the content is interesting for publication. The following comments may help to support the work of the authors.

General comments:

• As summarized from this study, the utilized data for simulation is taken from arbitrary sources. Thus, the validity should be carefully considered.
• The content is very interesting; however, I think the manuscript still needs further enhancement by considering other related geological, hydrological, and environmental factors into consideration.
• Omitted information related to the properties of the utilized aquifer in this study.
• The soil conditions that support this study should be considered.
• As seen, the authors established this model based on simple factors, however, other factors such as the type of aquifer, land activity and other factors have not been considered.
• It is not clear how we can verify the accuracy of the established model.
• Authors should clearly observe how they considered the groundwater vulnerability and pollution risk in the multi-criteria decision-making (MCDM) model.
• Based on this study, how can we determine the risks of the pollution and what are their effect on the presented results?
• Authors should add section identify the benefit of this work in the practical application.

Specific comments:

1. Abstract:

The abstract is long with total 272 words. Abstract should be the summary of a manuscript. It should include the problems, methodology to solve the problems and main points of conclusions. The length of abstract should be around 150 words. Please do not cite references in abstract.

2. Introduction

• It is necessary to illustrate the key factors related to the aquifer vulnerability variation.
• The introduction is interesting, but the gap of literature and the main contribution of this study, which is different from others should be clearly clarified.
• The advantages and drawbacks of the DRASTIC technology should be considered.
• It is necessary to add detailed information related to the dynamic effects of ground water in different applications. Besides, some recent well-written papers related to the dynamic effect of groundwater and related hazards are suggested to be added e.g.
• Lyu, H.M., Shen, S.L., Yang, J., Yin, Z.Y. (2019). Inundation analysis of metro systems with the storm water management model incorporated into a geographical information system: a case study in Shanghai, Hydrology and Earth System Sciences, 23(10), 4293-4307. https://doi.org/10.5194/hess-23-4293-2019
• Ni, J.C., Cheng, W.C., Ge, L. 2011. A case history of field pumping tests in a deep gravel formation in the Taipei Basin, Taiwan. Engineering Geology. 117(1–2): 17–28.
• Pujades, E., Carrera, J., Vázquez-Suñé, E., Jurado, A., Vilarrasa, V., Mascuñano-Salvador E. 2012. Hydraulic characterization of diaphragm walls for cut and cover tunnelling. Engineering Geology. 125(27): 1-10.
• Pujades, E., Jurado, A., Carrera, J., Vázquez-Sunè, E., Dassargues, A. 2016. Hydrogeological assessment of non-linear underground enclosures. Engineering Geology. 207 (3), 91–102.
• Pujades, E., De Simone, S., Carrera, J., Vázquez-Suñé, E., Jurado, A., 2017. Settlements around pumping wells: analysis of influential factors and a simple calculation procedure. Journal of Hydrology, 548, 225–236.
• Wu, Y.X., Shen, S.L., Lyu, HM, Zhou, A.N. (2020). Analyses of leakage effect of waterproof curtain during excavation dewatering, Journal of Hydrology, 583(2020), 124582, https://doi.org/10.1016/j.jhydrol.2020.124582.

3. Material and methods

• It is not clear how the authors can adapt the Weight settings for DRASTIC parameters?
• 6, Line 117: what is the main source of these utilized data?
• Figure 2 needs to be discussed in a good manner.
• 8, Line 165: Data on population density at the African scale for the year 1990, 2000 and 2010 were developed by SEDAC. What is the meaning of SEDAC?
• 8, line 166: how the authors can adapt and use the Ratings formula in this study?
• 9, line 175: authors need to clarify based on what they assumed that the parameter D is “static”.
• 10, line 181: omitted information related to how the authors can adapt the ratings of the map?
• 11, Line 202: the data adaption in ArcMap Raster system should be considered.

4. Results and discussion

• 5 needs to discuss in details.
• The difference between the results of Fig. 6 and Fig. 7 should be clearly observed.
• 16, Lines 260: There is no any clear difference between Fig. 8 and table 3.
• 17, Lines 271-301: Why the authors didn’t consider the land activity and type of aquifer into account?

5. GIS mapping:

Fig. 2 to Fig. 7 were drawn by GIS, however, they are not completely, e.g., lack of longitude and latitude. Moreover, you draw all of the Africa continent so that the map is too small, please enlarge Figs. 2 to 7 three times. Suggest to refer to the following publications:

• Peng J., Peng F. L., 2018a. A GIS-based evaluation method of underground space resources for urban spatial planning: Part 1 methodology. Tunnelling and Underground Space Technology, 74, 82-95.
• Peng J., Peng F. L., 2018b. A GIS-based evaluation method of underground space resources for urban spatial planning: Part 2 application. Tunnelling and Underground Space Technology, 77, 142-165.
• Lyu, H.M., et al (2020). Risk assessment of mega-city infrastructures related to land subsidence using improved trapezoidal FAHP. Science of the Total Environment, 717(2020), 135310. https://doi.org/10.1016/j.scitotenv.2019.135310
• Lyu, H.M., et al (2020). Inundation risk assessment of metro system using AHP and TFN-AHP in Shenzhen. Sustainable Cities and Society, 56(2020), 102103. https://doi.org/10.1016/j.scs.2020.102103.

6. Risk analysis. Analytic hierarchy process (AHP) and its series is an effective way to do risk analysis (Saaty, 2008; Li et al., 2013; Lyu et al., 2020). Suggest to do a discussion on the comparison between method in this study and AHP methods. Please present how you collect experts questionnaire? There are two approaches to do experts questionnaire: (1) one is the pairwise comparison, proposed by Saaty (2008), improved by Li et al (2013); (2) The second method to do questionnaire is to use table comparison proposed by Lyu et al (2020).

Li, F., Phoon, K.K., Du, X., and Zhang, M. (2013). “Improved AHP method and its application in risk identification.” Journal of Construction Engineering and Management, 10.1061/(ASCE)CO.1943-7862.0000605, 139(3), 312-320.

Lyu, H.M., Sun, W.J., Shen, S.L, Zhou, A.N. (2020). Risk assessment using a new consulting process in fuzzy AHP. Journal of Construction Engineering and Management, ASCE, 146(3), 04019112. http://dx.doi.org/10.1061/(ASCE)CO.1943-7862.0001757

Saaty, T.L., (2008). Decision making with the analytic hierarchy process. International Journal of Services Sciences, 1(1), 83-98.

7. Conclusions

1. 18, lines 318-321: Authors need to add more effective results. As it is well known that by increasing water demand, the groundwater vulnerability and pollution risk would also increase.

Author Response

Dear Anonymous Reviewer#2,

We addressed all technical corrections as requested. We thank the reviewer for his positive and critical appreciation of our manuscript. Please find below a detailed revision and reply report. In a separate file, the revised manuscript is submitted for your consideration. We have highlighted (blue colour) the sections in the manuscript which have been amended or re-written.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

no comments. sugegst to accept.