Analysis of Dry-Spells in the Western Maize-Growing Areas of South Africa
Round 1
Reviewer 1 Report
The authors studied the initial and conditional probabilities of dry-spell pentads using the Markov chain model in the western maize growing region of South Africa, and also analyzed the direction and magnitude of trends of dry spells using the Mann-Kendal monotonic trend test and Sen-slope estimator. The study is helpful for farmers regarding changes in the particular risk profiles of maize crops to dry spells.
The English language used needs extensive editing throughout with a high to moderate level of change required as there are many grammatical errors.
Major Comments
Authors should write extensive literature in the introduction section as there are only 12-13 in-text citations in the introduction.
For both figures 1 and 2, authors should redraw maps with quality. The authors also need to clearly display the spatial distribution of rain gauges in the study area.
I have serious reservations about the use of less than 15 mm rainfall per five days as dry pentad. Authors should have some already literature for a better threshold.
Lines 232-240: Authors should describe in detail which method of kriging was used and also describe what parameters were selected for kriging. As there are many satellite rainfall products (IMERG GPM, CHIRPS, etc,) available, authors should also explore these rainfall products instead of interpolation.
The authors also display long-term annual and seasonal rainfall for a better understanding of droughts and flood periods.
For all maps, the layers name should be clear in legend without any underscore sign.
Authors should rewrite the discussion by incorporating multiple similar studies in the study area.
Lines 158-162: Authors need to rewrite these lines as it is not clear.
Minor Comments
In Line 81, the authors are discussing multiple studies about the use of the Markov chain probability model but cite only one study.
Line 87: Please be consistent and follow numeric style instead of APA style during in-text citation.
Author Response
Please see the attachment
Author Response File: 
Author Response.docx
Reviewer 2 Report
Analysis of dry-spells in the western maize growing areas of 2 South Africa.
General comments:
This manuscript has an immediate application in the producer's decision to plant or not at a given time and even in public policy to be determined by agricultural managers. In addition to this publication, I would make another one more linked to the dissemination of technology, targeting typical producers in the region and using accessible language.
Why was data already available on corn productivity in this region and the predominant cultivar cycle not included and correlated with climate data?
Line 2: Comment: Include also wet-spells in the title? “Analysis of dry-spells in the western maize growing areas of 2 South Africa”
Line 4: General comments.
Line 28: Comment: Include rainfed in the keywords.
Line 28: Comment: Include wet-spells in the keyword?
Line 31: Comment: I would start the introduction by briefly describing the planting times in the target region and where maize falls.
Line 32/33: The production of maize in the country comprises of around 60% white and 40% yellow maize [1].
Comment: unnecessary information.
Line 34: The crop is consumed both in its physical and processed form as a starch [2].
Comment: unnecessary information.
Line 38: Maize production in 2019-20 season reached a high of 15,3 million tons [1].
Comment: If possible include recent information.
Line 40: Most of the production of maize in the 39 country is under dry-land production.
Comment: If possible, quantify it.
Line 44: One of the major limiting factors in dry-land production is therefore water stress, the consequences being delayed maturity and low crop yield. Comment: Frequently, maturity is advanced under stress. Do you have any explanation?
Line 45: Comment: I suggest a figure showing the dry spells and the phenological phase in which the most planted material is found in the region. May be here or in the discussion.
Line 63: Comment: I would use the word "trend" instead of behaviour.
Line 70/72: Consecutive wet-spells signal excessive surface run-off, which has benefits for water harvesting but requires mitigation measures to avoid soil erosion and potentially flood damage.
Comment: Run-off also may be avoid with organic matter such as mulch or greenmanure.
Lines 84/85: Climatologically, the western maize production region has a drier climate than the other maize production regions in South Africa.
Comment: Include bibligraphic citations here.
Line 101: Comment: Here, a figure over time including dry-spells and and wet-spells, phenological stage of the most planted maize cultivar in the target region would be quite didatic.
Line 117/119: Thus, the investigation of dry-spells is critical in this region as the 117 impacts of water stress have dire consequences on grain crop production, especially those 118 produced under dry land conditions.
Comment: This sentence is more appropriate for discussion.
Lines 122, 125, 266, 274, 278, 288, 311, 329...
Comment: figures /tables text needs to be self-explanatory.
Line 120/123: Comment: A third map with an even larger scale could be included in Figure 1.
Line 138: General comment: Why was data already available on corn productivity in this region and the predominant cultivar cycle not included and correlated with climate data?
Line 139/140: Daily district rainfall dataset was obtained from the South African Weather Service 139 (SAWS) rainfall database for a period of 30 years (1985 – 2015) [17].
Comment: Why wasn't more recent data included?
Line 157: The period of interest includes mid-January to end of February, which is represented by pentads 40 to 48, which is critical in the western region, as dry-spells tend to dominate this period and the crops planted in this region are usually in the drought sensitive flowering stage [2].
Comment: Again. It would be interesting to have a figure over time indicating when dry-spells occur while also indicating planting, harvesting and phenological stages.
Lines 232/250: Comment: Some of the information is more useful in the discussion than in the methodology.
Line 275: Table 3. Conditional dry-spell probability table (%) of SAWS rainfall districts during the mid-January to end of February period (pentads 40 to 48) from 1985 to 2015.
Comment: Need to include more recent data.
Line 322/325: These results further highlight that 322 this period is dominated by dry-spells and it is recommended that the analysis 323 should therefore focus on the occurrence of dry-spells and their future occurrences 324 within the study area.
Comment: The previous sentence would be more useful in the discussion than in the results.
Line 400: Knowledge on the length of dry-spells can be used for selecting drought tolerant varieties and can be used in irrigation planning during the critical dry period.
Comment: Here I would put a brief description of the predominant cultivars and how this improves or worsens water stress in this region.
Line 424/445: Rainfall patterns directly affect the crop yield in rainfed agriculture hence it is significant to monitor the probability of wet and dry-spells. The success and failure of crops in a planting season is directly influenced by the occurrence of wet and dry-spells. Dry conditions are beneficial during the ripening stage of crops. The rainfall districts that were analysed in this study reveal that the occurrence of dry-spells is a major threat to crops, where most summer crops in this region are at the flowering stage as they are planted later than the eastern regions.
For most districts in the study area, no notable changes were observed in the trends of dry-spell frequencies, except for one (district 92) which showed a decreasing trend in dry spell occurrence. However, this observed decreasing trend in dry spell frequency for district 92 was not statistically significant.
The recommendation from this study are as follows:
1. An investigation into optimum planting dates by using crop models to avoid the occurrence of dry-spells is conducted, which is crucial to assist farmers and decision makers in preventing production losses and other adverse effects of dry- spells.
2. The impact of climate change on future projections of the dry-wet-spells should be investigated.
Comment: Conclusions should be more direct so as not to be confused with discussion.
|
|
Comments for author File: 
Comments.pdf
Author Response
Please see the attachment
Author Response File: Author Response.docx
Reviewer 3 Report
Submitted paper falls into the scope of water journal and I found it as interesting and relatively well written paper. The article is focused on Analysis of dry-spells in the western maize growing areas of South Africa.
The manuscript still has need to improve, some issues and suggestion given below:
In the abstract is written well. In my opinion, line 16, 17, 18 is not important please define some important results.
The introduction section is written well but most of the references are repeated.
The keywords are appropriate for the manuscript.
Reference no 10 cannot find in the introduction section whenever it is included in reference section.
The discussion section still has need to improve please add some more reference which give support to present study.
In conclusion part please add the future research direction.
In the reference section most of the references are repeated in the manuscript such as 1, 2, 3, 4 please add some new references.
Suggestion
Line 53 start in October change into “start from October”
Line 126 rainfall districts 82 ,83,84…, please add the districts name with districts coding
Author Response
Please see the attachment
Author Response File: Author Response.docx
Reviewer 4 Report
The article is of interest for practical use in agricultural production, especially maize. This is an urgent work in connection with global climate change in recent years and an increase in the number of dry-spells. Droughts seriously affect crop yields and food security around the world. This problem is especially relevant for African countries, where many residents experience hunger due to lack of food. The authors are presented with a number of questions on research methods and suggestions for improving the presentation of results.
1. Reference to fig. 2 is better given in the form […].
2. In table 2 (climatic characteristics) for each indicator, it is necessary to provide quantitative values or ranges.
3. Section 2.2 indicates that the data range used is 1985-2015. Why didn't use the data for the last five years? Currently, climate change is fast and the use of up-to-date data is essential.
4. Since several estimation methods were used in the work, it is necessary to emphasize in the conclusions which of them are similar (most accurate) and can be recommended for further work.
5. In fig. 4 for each of the four areas presents different ranges of maximum and minimum values. It is not correct. It is necessary to give a range of 87-42 and present color gradations inside it. The same remark applies to Figure 5.
6. An important point in statistical evaluations is how the uncertainty of the analysis results was assessed and what value it is.
Author Response
Please see the attachment
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The authors have addressed most of the comments. The manuscript can be accepted if other reviewers have not any serious objection.
Reviewer 4 Report
The authors corrected most of the comments of the reviewers. I hope these corrections improve this article.
