Dear reviewer,

Thank you very much for your positive and constructive review.

When we revise our manuscript, we intend to incorporate all the suggestions. We have also responded to comments regarding confusion in understanding the manuscript.

Individual responses to the points you raised can be found below.

We will here respond to the main concern raised.

We acknowledge that the title we chose for our paper could be misleading in suggesting a broader content than what was actually investigated. We agree that the initial title, the abstract and introduction mentioning “drought impacts” suggested an investigation of all potential impacts including those mentioned in the review that we didn’t consider. Indeed, we focused only on food and water securities.

To align the study content and your pertinent suggestions, we will modify our title, abstract and introduction. We reformulated our title to “A geography of drought indices: the mismatch between drivers and impacts”. We aim to be clearer that the focus is on food and water related impacts early in the abstract and introduction.

On behalf of all co-authors,

Sarra Kchouk

Major comments

• The authors should emphasize that only impacts related to water security and food security are considered. This should be very explicit in the title, abstract, introduction and discussion. This limits considerably the scope of the paper as impacts related to forestry, energy security, transport and even tourism are disregarded. Furthermore, this results in a bias in the outcome regions with a higher number of studies. E.g. if forestry was considered, I think there would be more studies in EUA and Europe

We agree and will clearly state that the focus is on food and water related impacts early in the abstract and introduction.

• Line 99: It should be further stressed in the introduction that a country comparison was conducted. I think the way the search was done can introduce biases. It could be that a studied investigated, West African countries for instance or that it investigated the Tyrol region or it could also be that just the name of a City/state were mentioned and not the country itself.

We agree. We will include earlier in the introduction (l55) that the search was done on the base of the countries mentioned and not regions. We will also raise this point in the discussion; certain studies might be missed because they focus on regions rather than countries. We, however, expect that this effect is fairly evenly distributed across the globe and don’t necessarily expect it to introduce a bias.

• I would suggest making a correlation between the number of driver studies and the number of impact studies. You could either have a plot or a table with this for different countries or for different regions. This way we can visualize better the existing ratio. This will help to support your discussion. This could be used instead of Figure 4

Yes, thank you for the useful suggestion. A correlation between drivers and impacts would improve the visualization of the ratios and this will be incorporated in a new figure.

• Section 4.1, besides the descriptive analysis, I think a more critical judgment is needed here. What are important indices that are hardly applied? Why they are hardly applied?

Yes, thank you for the suggestions of analysis. We are explaining in this section 4.1, the preferred application of indices, over others, justified by the physical conditions of the area. In the three following sections, we bring other and deeper elements of analysis being the socio-economic conditions, the data availability and the scientific interest and orientation. We believe that these elements of analysis fall under what you suggest to further discuss. We also think that it can be difficult and out of the scope of our study to analyse what important indices are hardly applied and why, even if relevant. This would imply investigating and discussing what indices can be considered as important, which is another different research question.

Later in our recommendation section (4.5), we suggest to use indices based on the SDGs. We hypothesize that these are hardly ever applied in drought research because there are multiple factors that influence these indices, drought being just one of them. This calls for a complete change of perspective compared to the current paradigm in the drought/DEWS community – impact centred rather than drought centred.  As reviewer 3 formulated it in her/his review: what is the contribution of drought to food and water security? – rather than an assumed linearity between  drought indices and food and water security.

• The discussion in 4.3 is directly related to 4.1 I would suggest to join them.

We agree that both sections are directly related, the second depending on the first. However, both represent different problems that we believe are better discussed independently. Section 4.1 focuses on the climate and water resources of the area, Section 4.3 focuses on the capacity of a country for data collection and analysis. We suggest following your advice to some extent by making the current Section 4.3 directly follow 4.1 (so to be the section 4.2 in an updated version), and making the link between the two sections more evident.

• A main limitation is that the definition of drought impact is very narrow. Important studies related to forestry in Europe and USA were completely ignored, for instance. In the recommendation section, if would be beneficial to add that future studies could look into impacts for other sectors. Examples of papers that give a good overview of potential impact types that could be investigated include:

https://iopscience.iop.org/article/10.1088/1748-9326/aba4ca

https://nhess.copernicus.org/articles/16/801/2016/

Thank you very much for this suggestion and for the references that we will utilise. The limitations section will be extended incorporating this information. Both suggested references are great examples of how text mining (in these cases based on media reports) has the potential to advance drought research.

• A further limitation is that you work only with word frequencies. It could be that many of the impacts or indices are just mentioned in the abstract, but that the study does not really investigate it. For example, it could be that the abstract says “research is needed to help us understand food security”. You could perhaps manually validate part of the abstracts and see what is the percentage of papers that fall into this category. In any case, this limitation should be clearly stated.

We agree and will add this clarification to the extended limitations section. We will also conduct a manual check as suggested to evaluate how commonly impacts may have been mentioned but not investigated.

• Here you try to link drivers and impacts by using simple linear approach. There are some quite interesting studies that actually try to link these data. I suggest adding a paragraph to the discussion session regarding the linkage of the physical aspects to the socio-economic ones. Some suggestion of studies that could be used to write this paragraph include:

https://hess.copernicus.org/articles/20/2779/2016/

https://www.nature.com/articles/s41467-019-12840-z

https://iopscience.iop.org/article/10.1088/1748-9326/10/1/014008/meta

It was by no means our intention to give the impression that drivers and impacts are linked in a linear fashion. Rather, we discuss the important role of local context, which hampers any generally applicable linear link between the two. The suggested literature are indeed studies that aim to directly link drivers and impacts and are therefore of relevance to our manuscript. We would, however, like to go even one step further as also specified earlier in this review, and suggest to change the perspective: start from the impact rather than the drought driver, because drought is just one of many drivers that leads to the final impacts. We will add this to the discussion, including the suggested literature.   

 Minor comments

• Line 68: What is meant by “categorized” geographic areas?

We did not find the term “categorized” in l68 but in l58 at the end of the introduction; we assume that is what was meant. “Categorized” was used to mean “grouped” in the sense that we grouped the countries according to geographic regions. We will change this term, as suggested in one of the major comments.

• Line 75-76: The sentence is not clear. Metrics for what? Do you mean for selecting which indices were going to be reviewed?

Thank you for this comment. We meant by “metrics” the equivalent of “unit” and we will reformulate it to explain this more clearly in the manuscript.

• Table 1: please mention that this top 3 areas are retrieved from scopus

We agree and will amend the table as suggested.

• The Soil Moisture Index (SMI) is missing from the agriculture indices, or is it related to other of the mentioned indices? Please check. Here some references:

https://iopscience.iop.org/article/10.1088/1748-9326/11/7/074002/meta

https://hess.copernicus.org/articles/18/2485/2014/

Yes indeed, the SMI is missing from our listed agricultural drought indices. This is primarily because, as mentioned in our methodological section, we based our non-exhaustive list on two main publications: the IDMP handbook of drought indicators and indices (Svoboda and Fuchs, 2016); and a scientific study (Bachmair et al., 2016) where the authors gathered the most used drought indices in EWS by drought managers. In both publications, the SMI was not mentioned. A second reason is that we include very similar indices in AD indices: the Soil Moisture Anomaly (SMA), the Soil Moisture Deficit Index (SMDI) and the Soil Water Deficit Index (SWDI). We propose to include this clarification in the methodology section.

Bachmair, S., Stahl, K., Collins, K., Hannaford, J., Acreman, M., Svoboda, M., Knutson, C., Smith, K. H., Wall, N., and Fuchs, B.: Drought indicators revisited: the need for a wider consideration of environment and society, Wiley Interdisciplinary Reviews: Water, 3, 516-536, 2016.

Svoboda, M. D., and Fuchs, B. A.: Handbook of drought indicators and indices, World Meteorological Organization Geneva, Switzerland, 2016.

• Line 81-95: This information should come before the table 1

We agree and will move this paragraph before the table and adjust l77-78 accordingly.

• Figure 1: It is not possible to read some of the classes in the figure.

Indeed. We thought that it was not necessary for all the name of the indices to appear in the figure because the focus was to show the dominance of use of 3 main ones. We will change the dimensions of the figure and add leader lines.

• Line 122: I do not think there is a significant difference. For me they follow all the same pattern with some minor differences. “exceptions are Australia-Oceania and Sub-Saharan Africa, where AD indices are most frequently reported”. Can you add confidence intervals to the plot?

Thank you for the comment and suggestion. We don’t see an opportunity to include a confidence interval because what is represented is not a sample but all the studies we found by using the queries. However, we will include a label mentioning the share of each type of MD/AD/HD studies, in percentage, to make the difference appearing clearer.  

• I am not convinced of using the acronyms MD, AD, HD. The terms “meteorological drought”, “agricultural drought”, etc are not so long, and I think it would be better for the reader to use them instead of MD, AD and HD

We will use the full terms rather than the acronyms.

• Figure 2: If you opt to use the acronyms, it would be useful to add (MD), (AD), (HD) to the Figure. The acronyms are new and if you repeat then in the figures it makes it easier to read the text without needing to come back every time at the first time they were mentioned.

We will use the full terms in the text.

• Line 140: Again, I am not convinced of the use of SSA and similar acronyms. I had to go back in the text multiple times.

We agree. We will use the full terms.

• Figure 4: it is a nice plot, but does not add any new information. I suggest adding it to the supplementary material. I think this figure could be substituted by one where you show the ratio of driver vs impact studies.

Yes. We will elaborate the previously suggested figure. We will thus evaluate and compare the information brought by the current Figure 4 and consider whether to move it to the supplementary materials or integrate it to the Fig.5 to facilitate the reading of the cartograms.

• Figure 1: I like the innovative visualizations, but I think a traditional choropleth map would convey information in an easier way

We assume the reviewer refers to Figure 5. We opted for a cartogram for many reasons. Firstly, it is what we thought to be the most obvious way to eliminate a “visual” bias where there would be more studies because a country is larger. To eliminate this bias, the number of studies should be standardised to either the total number of studies (of MD, AD and HD) or the size of the country; which in our opinion introduced more uncertainty. Secondly, this type of visualisation is print and colour-blind friendly. A recent publication (Crameri et al., 2020) highlighted how colour maps visually distort data through uneven colour gradient and can be unreadable to those with colour-vision deficiency. Our aim was for the analysis and understanding of our figure to be independent from the used colours.

Crameri, F., Shephard, G. E., and Heron, P. J.: The misuse of colour in science communication, Nature Communications, 11, 5444, 10.1038/s41467-020-19160-7, 2020.

• Line 360: I would change “countries” by “regions”, as for most of the analyses you aggregated the data.

Our analysis is mainly presented at the continental level, but our data was analysed at the country level. Therefore, we would like to keep referring to countries.

• Line 413-414: I do not think the results showed that “Our results revealed that drought is mainly depicted through a conceptual lens”. I would remove the conceptual lens part as you have just focused on a word frequency and have not analysed the papers in detail

We will remove this statement,

• Line 358-363: This is not a limitation. The first sentences could be moved to the discussion above. The last sentences are a lot of speculation that should either be removed or backed up by other research

We agree that explaining the scale used for the search and the analysis of study (l358-360) is not a limitation. We propose to move these lines to the methodological section.

Lines 362-363 will be removed.

We thank the reviewer for the careful reading and comments aiming to improve the quality of our manuscript. 

We respond to all concerns raised by the reviewer in this Author’s response.

We acknowledge that the title we chose for our paper may have been suggestive of a different content than what was actually reported. We agree than the initial title mentioning “a review of drought indices” could be misleading, hence the unfulfilled expectations raised by the reviewer.

The study expected by the reviewer, i.e. “the pros and cons of each index related to different aims and regions” was not the focus of our paper. Our bibliographic search showed that the pros and cons of each index related to different aims have already been extensively covered in the literature (e.g. IDMP, 2016 ; Bachmair et al., 2016; Bachmair et al., 2015 ; Zargar et al., 2011 ; Sivakumar et al., 2011 ; Yihdego et al., 2019). We also believe that it would be difficult to summarise an in-depth analysis of drought indices by region in a brief paper. Instead, we targeted our study to review some of the most used drought indices for meteorological, hydrological and agricultural drought. With regard to drought impacts we decided to focus on impacts related to food security and water security.

IDMP (2016). Handbook of drought indicators and indices, (M. Svoboda and B.A. Fuchs). Integrated Drought Management Programme (IDMP) Tools and Guidelines Series 2. World Meteorological Organization (WMO), Geneva, Switzerland and Global Water Partnership (GWP), Stockholm, Sweden.

Bachmair, S., et al. (2016). "Drought indicators revisited: the need for a wider consideration of environment and society." Wiley Interdisciplinary Reviews: Water 3(4): 516-536.

Bachmair, S., et al. (2015). "Exploring the link between drought indicators and impacts." Natural Hazards and Earth System Sciences 15(6): 1381-1397.

Zargar, A., et al. (2011). "A review of drought indices." Environmental Reviews 19: 333-349.

Sivakumar, M. V., et al. (2011). Agricultural Drought Indices. Proceedings of an Expert Meeting: 2-4 June, 2010, Murcia, Spain, WMO.

Yihdego, Y., et al. (2019). "Drought indices and indicators revisited." Arabian Journal of Geosciences 12(3): 69.

Since we took a human-centered perspective, we believe that our findings contribute to the field of socio-hydrology and to the science of drought indices showing how local and contextual circumstances channel the choice of which drought indices to use. This constitutes for us the relevance for the scientific community.

We also posit in our study that the integration of local context and impacts into drought indices would add benefit, leading to more accurate drought monitoring. We believe that this is a significant outcome of our study and a conclusion that is applicable for mitigation and adaptation strategies, as the Reviewer mentions.

Therefore, we have reformulated our title to “A geography of drought indices: the mismatch between drivers and impacts”. We believe this new title more accurately frames the content of our study.

When we have the opportunity to revise our manuscript, we plan to incorporate all the reviewer’s suggestions, as specified below.

On behalf of all co-authors,

Sarra Kchouk

• Did you use the NHESS templates for the manuscript and bibliography? especially the references look weird

We did use the NHESS template available from their website for the manuscript and we used the reference style “Copernicus publications” (in EndNote) that we also downloaded from NHESS website. We will manually assess the references and check individually for any errors.

• Line 40ff. You state, that the initial driver for agricultural and/or hydrological droughts always comes from meteorology. I do not agree. You can have normal precipitation conditions but excessive land use and water extraction that could lead to AD and HD.

Typically, *in the literature*, the propagation of drought is depicted as a linear process rooting from meteorological drought and leading to AD and HD. We agree with your comment and will re-write it more clearly.

• For Table 1 you made a selection. Is there a chance to estimate the dark numbers of indices, that exist and that are not listed in this Table? I also miss relative indices like the effective drought index by Byun and Wilhite (1999). Furthermore, the table caption should be at the top of the Table not at the bottom. At the end of the Table some lines are highlighted in yellow, is there a reason for that?

Indeed, we have not included all existing drought indices, which would be an impossible task. Rather, we selected those indices that have been listed in two main publications summarizing the most utilised drought indices. These two publications are :  the IDMP handbook of drought indicators and indices (Svoboda and Fuchs, 2016); and a scientific study (Bachmair et al., 2016) where the authors gathered the most used drought indices in EWS by drought managers.

It was an error to place the caption below the table. It will be placed at the top of the table.

The lines highlighted in yellow were aimed to attract the attention of the reader and emphasise how some categories of drought indices and the impacts groups were studied through the social science scope; a crucial point mentioned in our discussion. We can make a clearer reference to this detail of the results in the discussion section.

Bachmair, S., Stahl, K., Collins, K., Hannaford, J., Acreman, M., Svoboda, M., Knutson, C., Smith, K. H., Wall, N., and Fuchs, B.: Drought indicators revisited: the need for a wider consideration of environment and society, Wiley Interdisciplinary Reviews: Water, 3, 516-536, 2016.

Svoboda, M. D., and Fuchs, B. A.: Handbook of drought indicators and indices, World Meteorological Organization Geneva, Switzerland, 2016.

• Line 100ff. The reasons how you select the studies and indices is definitely not clear to me

We selected all the studies where the drought indices of Table 1 were mentioned in a drought-related study. The reasons *why* we selected these indices are the reasons mentioned in the answer to the previous Reviewer’s comment (#3). The reasons *why* we selected these studies was to retrieve their (primary) country of application. The exact queries showing *how* we proceeded are available in the Table A1 of the appendices. We propose to make these two points clearer in the methodology section.

• For the figures like Fig.5, there should be a short explanation in the text of what this type of displaying represents and how to interpret such figures. Also, what do the squares in the bottom left corner of each figure stand for?

Indeed. We will add a short explanation of how to read the cartograms. The squares are the legend indicating the number of studies according to the size of the country. We will add this to the explanation in the text and the figure caption, in addition to the world “legend” above those squares.

• There are some error messages in the text for missing references. Lines 241 and 278

The error messages have been corrected in the preprint that is downloadable on the NHESS website.

• Lines around 250, I was expecting the total study more in this way like it is done for the SPI

We decided to go into such detail for the SPI as it is globally the most used drought index while being one requiring the fewer variables. Providing this level of detail for all the other indices would not have been feasible in a brief paper. Also, as we explained in our short response, this was not the aim of this paper; rather we aimed to explore the impacts component and the geography of both drivers and impacts.

Dear reviewer,

Thank you very much for your positive, constructive and highly encouraging review, that will certainly improve the quality of our manuscript.

When we revise our manuscript, we intend to incorporate all the suggestions.

Individual responses to the points you raised can be found below.

On behalf of all co-authors,

Sarra Kchouk

Comments related to findings:

• Line 221: In this paragraph or the next, it would be relevant to mention governance and/or corruption, some of the factors other than physical and demographic conditions that are widely recognized as contributing to food insecurity.

Yes, thank you for the useful suggestion. We will dive into the literature to discuss the role of governance and corruption in food security and include this analysis in section 4.2.

• Paragraph starting on 231: You could also conclude that focusing on physical drivers of drought is a “luxury,” more apt to be of interest in places where more basic needs such as food security have been met.

Thank you very much, this is a very good point, which we will add to section 4.2.

• Line 275: The sentence starting with “One reason …” is probably off the mark, overly concerned with definition, implying that people are somehow dismissing studying hydrologic drought because it’s an impact and less worthy of study. It seems more likely that hydrologic monitoring is very local and conditional, directly related to water supplies, and data probably isn’t shared, subject to the socio-economic conditions described in the preceding paragraph. Bottom line, researchers in those countries lack incentives and/or data to do the work.

We agree with the reviewer and the sentence will be amended to include the suggestions accompanied by bibliographic references.

• Line 291: I usually think of a “driver” as a meteorologic or physical system or condition that creates drought, which is measured by a drought index.

We agree with the reviewer and believe a typo created this confusion. Earlier in the text (l35) we provide a definition matching the reviewer’s suggestion. We will reformulate the sentence to read: “The indices linked to the three categories of drought are seen as drivers as they refer to the contributing or counteracting meteorological or physical factors that affect the development of droughts. They are used to determine the occurrence and severity of a drought. However..”

• Line 293: Rather than saying it is not clear, perhaps state that it is context-dependent.

We agree with the reviewer and will rephrase the sentence as suggested.

• Line 300: It is well-established that human-driven demand affects water security, along with the hydrologic system. You could say this is consistent with Van Loon et al 2016.

Thank you for the suggestion. We will include this reference to strengthen our statement.

• Line 320: The sentence starting on 321 is a bit of a contortion. How would food security NOT be related to these social processes? And what is “food security related to drought studies”? Food security as seen through the lens of drought studies? Just trying to construct this sentence suggests that too much focus on drought obscures the larger goal.

We tried to tie the discussion as much as possible to our methodology which was based on retrieving studies mentioning “drought” and the keyword of interest. Thus, by “food security related to drought studies”, we meant the studies mentioning “drought” and an impact linked to food-security. We will rephrase it as: This indicates that in drought-related studies focused on SSA, food security and the occurrence of these social processes may be closely related.

• Line 346: It’s not drought indices that are eluding monitoring of social processes that contribute to impacts. It’s the focus of inquiry or intent. A drought index is one thing. Variables or indices related to food or water security are another piece of it. There may be many pieces in a bigger system.

Thank you for the suggestion, we agree. The focus here was on drought indices while it should have been on the monitoring systems that only use this type of information. What contributes to an incomplete prediction of drought impacts and their severity is the omission in those monitoring systems of indicators depicting social processes. We will rephrase this part.

• Line 351: Drought and a related variable such as food security may be directly related, or drought may be one of many stressors in a complex food system. Aligning a drought index and some kind of impact variable is a good start but given the complexity of the systems in question it is unlikely that drought would have sufficient explanatory or predictive power on its own. I think this is actually what you are saying but the final sentence of this paragraph is a bit murky.

Yes, that is the point that we are attempting to make. We will rephrase this paragraph according to your suggestion that seems to convey the main message in a clearer way.

• Line 360: Final sentence may not be needed.

Yes, thank you for the suggestion. We will delete it.

• Line 363: “might be centralizing the background work” ??? reword, please

Yes, this was speculation that Reviewer 1 also pointed out. We will delete this sentence.

• Line 364: This is an extreme understatement.

We will develop this point further and add supporting references

• Lines starting with 378: Clarify this paragraph. Is this study about increasing the relevance and utility of drought-related variables? Or about framing questions that put drought-related variables in appropriate context, and appropriate relation to one another?

Indeed, there is a mistake in line 380. It is not about drought-related variables but drought monitoring systems mainly relying on physically-based indices. We will correct this and incorporate your suggestion of mentioning that our study also contributes to “put drought-related variables in appropriate context, and appropriate relation to one another”.

• Paragraph starting on 392: Yes, yes, yes! … Does this suggest the basis for a next bibliometric study, analyzing the role of drought in research on Sustainable Development Goals? Do your results shed new light on how researchers are or are not incorporating DEWS into development efforts?

At this stage, we don’t believe we can directly draw conclusions based on our results on how DEWS are part of development efforts. Therefore, we will develop this paragraph further and provide suggestions for future research.

• Line 385: Or thinking bigger than drought mitigation, to mitigation of food and water insecurity, in which drought plays a role. You have this in the sentence starting on Line 390, but take a convoluted route to get there.

We agree and will rephrase that sentence to align better with our statement in line 390.

• Could mention somewhere: Institutional incentives in many western countries may favor research that falls into well-defined silos. Research that meaningfully incorporates both physical and social science may not be sufficiently interesting to merit ground-breaking publications on both fronts; it may instead require one or the other discipline serving in a more consultative role.

Thank you for this suggestion. We agree and will include this point in the final paragraph of our section 4.4. Scientific Interest and Orientation, in a new paragraph starting at line 308.

Minor:

• Line 182: Either delete “a” or the “s” on “events”.

Thank you; we will delete the “a”.

• Line 201: “dry” not “dryer”

Thank you; we will correct it.

• Line 230, probably “population” instead of “demography”

Yes, population (growth).

• Line 318: Extra word?

Yes, “heatwaves” will be deleted.

Dear reviewer,

Thank you very much for your positive and constructive review.

We will here respond to the main concern raised.

During the preliminary research that lead to the results mentioned in our study, we did indeed conduct a time analysis. We visualised and compared the timely evolution of the usage of drought indices and drought impacts in the literature in order to analyse and link it to the same factors that you mentioned. However, we did not find any remarkable pattern, peak or correlation. Therefore, we decided to not include this part. We do recognise however that this should have been mentioned in our manuscript as it is a main concern that may arise.

When we revise our manuscript, we intend to incorporate your suggestion by mentioning that a time-analysis of the usage of the indices has been done and no clear changes in reported indices over time were observed.   

On behalf of all co-authors,

Sarra Kchouk