Influence of initial soil moisture in a regional climate model  study over West Africa – Part 1: Impact on the climate mean

Koné, Brahima; Diedhiou, Arona; Diawara, Adama; Anquetin, Sandrine; Touré, N'datchoh Evelyne; Bamba, Adama; Kobea, Arsene Toka

doi:https://doi.org/10.5194/hess-26-711-2022

Articles | Volume 26, issue 3

https://doi.org/10.5194/hess-26-711-2022

© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/hess-26-711-2022

© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 26, issue 3

Research article

|

11 Feb 2022

Research article |

| 11 Feb 2022

Influence of initial soil moisture in a regional climate model study over West Africa – Part 1: Impact on the climate mean

Brahima Koné, Arona Diedhiou, Adama Diawara, Sandrine Anquetin, N'datchoh Evelyne Touré, Adama Bamba, and Arsene Toka Kobea

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Final revised paper (published on 11 Feb 2022)
Preprint (discussion started on 08 May 2020)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC1: 'Reviewer Comments', Anonymous Referee #1, 17 Jun 2020
- AC1: 'Reply to comments of reviewer 1 (RC1)', Arona Diedhiou, 04 Aug 2020
RC2: 'Review of Part I', Anonymous Referee #2, 24 Jun 2020
- AC2: 'Reply to comments of reviewer 2 (RC2)', Arona Diedhiou, 04 Aug 2020

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (further review by editor and referees) (05 Aug 2020) by Shraddhanand Shukla

AR by Arona Diedhiou on behalf of the Authors (03 Sep 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (20 Sep 2020) by Shraddhanand Shukla

RR by Anonymous Referee #1 (27 Oct 2020)

Suggestions for revision or reasons for rejection

Second Revision of HESS-112: Influence of initial soil moisture in a Regional Climate Model study over West Africa: Part 1: Impact on the climate mean

The authors have responded to all initial comments and have, for the most part, revised the manuscript accordingly and satisfactorily. I have a few comments below that either still need further input or are new comments. Overall the manuscript still needs minor revision before publication. One of the weaknesses in the paper still remains in its use of the English language, there are a number of sentences that do not make sense or are run-ons. Additionally, I think the authors could still add some description fo their introduction and summary/conclusion to make the paper flow better.

Major Comments:

1. One of the main concerns of both reviewers and the editor was your use of only 2 years in the study. I don't understand your reasoning noted in your response to the editor that since the sensitivity to initial soil moisture anomalies is only one season you only need two experiments. I still find this concerning, though the authors have at least provided references that show this experiment design in use in other papers.

In the concluding remarks the authors seem to imply that this experiment was to estimate the limits of the impact of internal forcing and these are more idealized results. This makes more sense to me, but you must note that these are more idealized results. I think it might be best to state that very prominently in the introduction in order to guide the reader through what you're achieving and the limitations of this study.

It may also be prudent to include the Figure with "wet" and "dry" years that was included in the author responses to give the reader some indication of how "extreme" these years were. This Figure wasn't included in my review report for some reason, so I'm not sure if its the same as something already included.

2. With respect to my initial comment 3 on the normal distribution. I am aware that the use of the normal assumption is not new. My question is whether you think it is appropriate to use that assumption here. For example, precipitation is better approximated with a gamma distribution on seasonal timescales, etc. The approximation of normal can be problematic for variables that are not normal, and this may be the case here.

3. You have an entire section on how your experiments influence surface fluxes but only devote a line to these results in the concluding remarks, which makes me think that they are less important. Please add some context to the concluding remarks on why these results are significant to this experiment design and the field.

4. Similarly I think your end of section summaries could be improved and put into the context of your experiments. For example, line 447 - 450 you discuss the cooling and warming of surface temperature, but what does that have to do with your wet, dry, etc. experiments?

Minor Comments:

1. Line 41-45: References are needed.

2. Avoid language like "tends to cause", etc. as it lessens the impact of the results.

3. You've introduced some abbreviations and didn't use them continuously, please make sure you did this. E.g. page 7 "mean bias" vs. "MB".

4. Line 230: What do you mean by "peak mode of change"? You had been previously saying "peak of change" - Which I'm also not sure what that means. Do you mean "maximum change"?

4. Grammatical Comments: I'm not going to list all of these, but I suggest you still revise your manuscript for English language. There are a number of places that the sentences don't make sense, are "clunky", or just are incomplete. A few examples are below:

Line 36: "The strength of soil moisture impact on land-atmposphere coupling is variable according to the place and with the season." You can simply say: "The strength of soil moisture impacts on land-atmosphere coupling varies according to location and season" and this will greatly improve the clarity of the sentence.

Line 91: "The scheme of the large-scale precipitation used is from Pal et al. (2000), the moisture scheme is the SUBEX (SUBgrid EXplicit moisture scheme) takes in account the cloud variability scale sub-grid, and the accretion processes and evaporation for stable precipitation following the work of Sundqvist et al., 1989." Can be restated: "The large-scale precipitation scheme is from Pal et al. (2000) and the moisture scheme is the SUBEX (SUBgrid EXplicit moisture scheme). The SUBEX take into account the sub-grid scale cloud variability, and the accretion processes and evaporation for stable precipitation following the work of Sundqvist et al., 1989."

Line 114: The uncertainties reduction related to the absence of reliable observation system over the region (Sylla et al., 2013a; Nikulin et al.,2012), we validated the simulated precipitation based on two products..." I'm not sure what this means.

Line 172: "In the aim to identify the extreme years (driest and wettest) impacted by the dry and wet experiments among the five years simulations (2001 to 2005), we display Changes in daily soil moisture for 5 years (2001 to 2005) and their climatological mean during JJAS over West African domain, from dry and wet experiments with respect to their corresponding control experiment in Figure 2." This is a run-on and clarity would be increased if it were simplified.

Line 188: "...for JJAS 2003 and JJAS 2004 and their corresponding simulated from control experiments..." And their corresponding what?

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RR by Anonymous Referee #2 (04 Nov 2020)

Suggestions for revision or reasons for rejection

I appreciate the edits the authors have made to the manuscript. The authors, however, did not address one of my main concerns, which was that even as a sensitivity analysis their choice of permanent wilting point and field capacity may be rather extreme. I believe either the authors misunderstood my comment, or I am misunderstanding their methods (either is possible).

In my comment 4 I expressed concern about the authors using a global value for wilting point and field capacity, because in reality both of these values change dramatically within their domain. The authors cite the methods of Hong and Pan (2000), but in Section 2.2. of that study the authors say that "the version of soil model used in this study uses a uniform vegetation fraction and soil texture value over land", which would produce global values of field capacity and wilting point in their model, making the use of single global values (0.1 and 0.47) analogous to the use of local values.

If the model that the authors use in this current study does not use a uniform soil texture and vegetation fraction, then the soil model would not have uniform values for wilting point and field capacity. I am not familiar with the model so I cannot say if this is the case. I would ask that the authors clarify for the reader either that (1) their soil model uses uniform values of wilting point and field capacity (as does Hong and Pan, 2000) or (2) be clear that even though their soil model has spatially varying values of field capacity and wilting point, that they use a single global value. I ask this only so that readers will be able to follow the methods the authors are using.

Lines 18-20 in the abstract stating that "we initialized the soil moisture at the wilting points and field capacity with dry and wet soil moisture initial conditions", for example, is untrue if the authors are using a model that has spatially varying wilting points and field capacities, but initializing all locations using a single value. The authors could instead say that they initialize the soils at volumetric fractions of 0 and 0.49 everywhere, which would be more clear for the reader.

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ED: Publish subject to revisions (further review by editor and referees) (16 Nov 2020) by Shraddhanand Shukla

AR by Arona Diedhiou on behalf of the Authors (28 Dec 2020) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (10 Feb 2021) by Shraddhanand Shukla

RR by Anonymous Referee #2 (15 Feb 2021)

RR by Anonymous Referee #1 (23 Apr 2021)

Suggestions for revision or reasons for rejection

HESS-112 Review

This is the 3rd revision to HESS112: Influence of initial soil moisture in a Regional Climate Model study over West Africa: Part 1: Impact on the climate mean. Please see my comments below. I recommend major revision.

Comments:
1. I appreciate that the authors took the time to send the manuscript for English language editing, but I found a mistake in the first sentence of the paper, and a number of oddities in the first paragraph. While the authors sent this out for editing they should still re-read it for flow and inconsistencies.
(a) In the climate system, soil moisture is a crucial variable that influence[s] water balance and surface energy components...
(b) Line 47: "Another potentially useful earth system component that varies slowly is soil moisture" - You've already introduced soil moisture. It seems like you're introducing it again. You actually could just get rid of this sentence.
(c) "One important role of anomalies in soil moisture in the coupling of land and atmosphere has been shown in several studies, using numerical climate models (Jaeger et al., 2011; Zhang et al., 2011) and observation datasets (Zhang et al., 2008a; Dirmeyer et al., 2006)." What is the important role?
(d) However, at local and regional scales, the land-atmosphere coupling studies with AGCM[s]...
(e) Line 65, define RCMs.
(f) Overall, the results of these studies show that, during summer, the strong impact of the anomalies of soil moisture in land-atmosphere occurred mainly over the transition zones with a climate between wet and dry climate regimes, [in agreement with Koster et al.]
(g) Line 75: This study will focus on the influence of initial soil moisture conditions anomalies. Remove either conditions or anomalies.
... Again, I'm not listing all of these instances. The authors need to be more proactive in their read-through of the paper.

2. Perhaps I missed it but I'm still confused about the experiment design. Are these ensemble experiments? I.e. does your wet initial soil moisture condition experiment (for example) have ensemble members of precipitation and temperature, or is it just one model run? I just want to make sure I'm understanding this correctly. I might note somewhere that you have 1 realization of precipitation and temperature (or its an ensemble) for each soil moisture initial condition just to make this abundantly clear.

3. Are the soil moisture initial conditions soil moisture anomalies? Make sure this language is consistent.

4. This comment goes for both hess112 and hess113. I'm not entirely satisfied by your statistical significance test using a t-test. If I'm understanding your experiment design and statistical significance test correctly, this is a two-sample t-test of means - You've compared your control (sample 1) to the sensitivity test (sample 2). Are you doing this for 1 year only, for your entire study period? For a two sample t-test you need to assume the values are independent, and I'm wondering if they truly are independent samples. Both reviewers have made notes about your significance test asking specifically fore the sample size used and it has not been adequately provided. Some of these questions might be answered if the authors better explained their significance test procedure.

5. Line 460: The strongest precipitation decrease (increase) is found over the central Sahel (over central Sahel) in dry (wet) experiment in JJAS 2003 (JJAS 2004) with maximum change reaching -4% (40%). You don't need that parenthetical reference for the central Sahel twice. In addition, and I think I've noted this in some of my earlier reviews, over-use of this style of writing can be very confusing for long sentences. You could just make this into two sentences instead of using the () style.

6. It would be good to re-iterate how these results fit into the greater body of literature in your concluding remarks. For example, how this has not been quantified for West Africa, and these are very idealized experiments meant to provide what is essentially a first look or guess of what the impacts of soil moisture initial conditions might be in the region. These results are also likely very specific to RegCM4. The authors could also speculate about further work that could be done given the results of these experiments.

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ED: Reconsider after major revisions (further review by editor and referees) (01 Jun 2021) by Shraddhanand Shukla

AR by Arona Diedhiou on behalf of the Authors (13 Jul 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (03 Oct 2021) by Shraddhanand Shukla

RR by Anonymous Referee #3 (19 Nov 2021)

ED: Publish subject to minor revisions (review by editor) (03 Dec 2021) by Shraddhanand Shukla

AR by Arona Diedhiou on behalf of the Authors (12 Dec 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (20 Dec 2021) by Shraddhanand Shukla

Short summary

The impact of initial soil moisture anomalies can persist for up to 3–4 months and is greater on temperature than on precipitation over West Africa. The strongest homogeneous impact on temperature is located over the Central Sahel, with a peak change of −1.5 and 0.5 °C in the wet and dry experiments, respectively. The strongest impact on precipitation in the wet and dry experiments is found over the West and Central Sahel, with a peak change of about 40 % and −8 %, respectively.