Managed Aquifer Recharge as a Low-Regret Measure for Climate Change Adaptation: Insights from Los Arenales, Spain

Round 1

Reviewer 1 Report

As it stands, the title gives the impression that the article is intended to make a general (i.e., worldwide?) “low-regret” statement on the application of MAR to mitigate the effects of CC, particularly with its reference to developing countries.  The “low-regret” statement is certainly true for the Los Arenales MAR systems as aptly reasoned in the manuscript.  However, these systems were all constructed in a thick sandy aquifer needing relatively inexpensive recharge systems with little maintenance, and, if necessary, could even have accepted slightly less than perfect water quality.  These are not fully representative of the wide range of MAR applications found around the world.

It would have been convincing if a variety of MAR systems were considered, operating in diverse aquifer types e.g., using the data of 28 MAR schemes worldwide in Zheng et al., 2021 (Zheng, Y., Ross, A., Villholth, K.G. and Dillon, P. (eds.), 2021. Managing Aquifer Recharge: A Showcase for Resilience and Sustainability. Paris, UNESCO).

Figures:

The figures are largely in disarray:

1. (p. 4) The location of the study sites and aquifers: this figure seems to be in the right place, but it is interrupted by text lines 126 to 129.

1. (p. 5) Water management challenges: this is also labelled as Figure 1. However, in the text (line 154) it is referenced as Figure 2.

This figure’s caption is also incorrect as the past challenges and MAR solutions (in blue) are on the left while the CC challenges and MAR solutions (in orange) are on the right and not vice versa as in the caption.

2. (p. 8) The decrease in groundwater levels: this is first alluded to in line 133 (p. 4), but not referenced at this stage.  It would make sense to reference it at line 133 and to place it on page 4.  Obviously, it can again be referenced on page 8 line 295 (where it is referenced as Figure 3).

3. (p. 9) Groundwater pumping energy consumption etc.:

4. (p. 10) Discrepancies exist between data in graphs c) and d) where they overlap, and this is noted in the caption, but no attempt is made to lead the reader to understand what to make of the differences.

5. (p. 11) The relevance of the picture of the group of people is unclear.  The detail regarding the water body is too little to promote further understanding of its importance.

6. (p. 12) Although it is understood that irrigation helps to prevent the decline in the rural population the relevance of the “with irrigation/no irrigation communities” regarding “low-regret” MAR is unclear.  The text in this figure is difficult to read and it needs improvement.

Other issues:

Line 292: should read “average annual water levels”; also, in the legend of Figure “2” (p. 8); and in the figure caption (line 306).  The “average groundwater level” would be a straight horizontal line on the graph (just like the average annual precipitation).

Also, line 292, “year-1”: the “-1” should be a superscript.

Line 311: Table 1 is mentioned but there is no such table.

“Figure 3” (line 325, p. 9) is not referenced in the text.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

This manuscript gives a new way to see the benefits of managed aquifer recharge using a "new" concept of low-regret measures to adapt to CC by integrating some of the social and environmental services MAR systems provide. The authors document it in Los Arenales MAR systems considering their knowledge on these, including some that hadn't been considered to mitigate flooding and decrease the impact of droughts and water scarcity.

General comments:

The manuscript requires a complete reorganization:

The results section presents and discusses the research results, giving information that can be best placed in the introduction section. The discussion of the results must be moved to the discussion section. Rewrite this section or rename Results and Discussion.

By another hand, the discussion section does not discuss the results. The section starts with some conclusions and explains how the low-regret measures can be applied in developing countries. The authors hadn't mentioned anything about it before. The authors must focus the discussion on your results. Rewrite the section.

1.       Because the MAR system use water from surface flows, include the drainage system in figure 1.

2.       Include in figure 1 the location of wells for groundwater levels. (section 2.2.1).

3.       The numbering of figures is wrong and must be corrected

4.       Line 164, 178, 216, 230, 239, 241, 246, 269. LA must change to LAA or LAGB?

5.       MC is not defined, and it is used several times.

6.       Review reference, I found one that is not available anymore.

7.       (Line 256) Cita 76 is not available; please change it.

8.       The methodology section includes several arguments to support the methods used. This section must be reduced by just including the information relative to how data were obtained.

9.       (Lines 272 to 281) The first paragraph of the Section Flood severity and frequency (lines 272-280) explains the CC prediction models that interpret the flood severity and frequency. This explanation can be relocated to the introduction section.

10.   (Line 292) LA must change to LAA or LAGB?

11.   (Lines 292 to 294) It is important to explain how you get the average because you have 2 wells from 1985 to 2001 and 8 from 2003 to 2020, but you do not have data for 2002 y 2003.

12.   The left Y axis of figure 3 must say the relative groundwater level (m)

13.   Figure caption of figure 3 must say the average annual precipitation in Los Arenales groundwater body extension. Area

14.   I recommend commenting the positive trend of groundwater levels against a reduction of precipitation in the period of MAR implementation.

15.   (Lines 301 to 304) The second paragraph in section 3.1 must change to the discussion section.

16.   (Line 312) I couldn't identify the 22% commented on in the section Energy cost in figure 4. It could be an error.

17.   (Line 314) Reference to the work of Villamayor-Tomas y Fernandez Escalante in the Energy cost are not results of this work must be relocated to the discussion section.

18.   The caption of figure 5 is wrong. Please verify the order of the graphs.

19.   There has been an increase in the population from 2000 to 2014. Can you explain this? It is important because other factors seem to influence the population's dynamic, and it could be hard to identify the importance of water availability in population fluctuations.

20.   (Lines 342 to 347) The second paragraph on the Rural population doesn't provide enough arguments to prove the hypothesis that MAR provides sustainable irrigation to retain the rural population.

21.   The role of MAR in maintaining irrigation lands from 200-2014 without affectation on the groundwater level can be better illustrated, including the graph of groundwater levels on the right Y axis of figures c and d. (lines 338 and 339).

22.   Paragraph (lines 373-377) can be reallocated to the introduction.

23.   (Lines 420 to 449) Section 3.6 of surface water availability present the results and discusses them, but it is not clearly related to low-regret measure to adapt to CC.

24.   (Lines 450 to 465) In Section Drought severity and frequency, the authors present results from other authors but not related to the low-regret measure to adapt to CC. Please include some analysis of the influence of MAR in drought from a low-regret measure point of view.

25.   The caption of figure 7 (lines 432 a 435) is pretty confusing. Mainly figure 7b, if it is the percentage of the average MAR volume, why Avr. MAR is 1?. I recommend including the title of the Y-axis.

26.   (Lines 466 to 484) The flood severity and frequency title section is not the proper name for this section. It could be better: Flooding control or flooding reduction.

27.   Line 486 is a conclusion. Please change to the appropriate section.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

This paper is considered as a quite interesting scientific work showing that Managed Aquifer Recharge (MAR) can be employed as a low-regret adaptive measure to confront the adverse effects of climate change on water resources. The subject is within the topics of the Water Journal. The manuscript is clearly written following a structure that contains information, analysis results and discussion documented and presented in a sufficiently informative and explanatory way. Please find all relevant recommendations in the attached pdf review file.

Comments for author File: Comments.pdf

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The revised title aptly describes what the potential reader can expect.  Modifications to the introduction, particularly in the last paragraph, support the new title.  This immediately increases the value of the manuscript and makes it publishable.  Further, the figures that were largely in disarray are now well-organized and basically all of them were modified to enhance their contribution to the understanding of the overall message.

 The addition of Table 1 to the manuscript has a further benefit as it lists the depths of observation boreholes which provide a useful indication of the real magnitude of the aquifers used for MAR.

Author Response

Dear reviewer,

We are glad this new version has appropriately addressed your suggestions and concerns. Thank you very much for taking the time to review it.

Kind regards, 
Jose Henao