Dear Authors,

based on the reviewers' comments and your replies, I believe that your manuscript requires major revisions. When revising your manuscript according to the valuable suggestions and comments by the referees, I expect that you will address the following key issues:

- to highlight the difference between drought and low flow in the introduction (a good reference could be also found in Chapter 8 of the following book: Jose D. Salas, Charles N. Kroll, Antonino Cancelliere, Bonifacio Fernández, Jose A. Raynal, and Dong R. Lee Statistical Analysis of Hydrologic Variables: Methods and Applications. 2019);
- to clarify both the objectives and novelties of the paper with respect to the state of the art knowledge;
- to provide a clear logical connection among the methodological approaches adopted in the study, since so far they appear barely linked;
- to justify why operation rules are not taken into account in the reservoir storage analysis;
- to have your manuscript proofread by a native English speaker.

I look forward to receiving the revised manuscript.

Best regards,

Brunella Bonaccorso

Dear Authors,

after receiving reports from Referees #1 and #2, who expressed opposite opinions about the final decision on the revised manuscript, I decided to ask for further comments from two additional referees. Following their reports, I strongly invite the authors to make an extra effort to improve their manuscript based on their suggestions, with special reference to the ones by Referee #4, that partially overlap with previous comments by Referee #1, although less severe. The authors must be aware of the fact that a thorough and responsive revision of the manuscript is crucial for a positive outcome of the review process.
I very much rely on the ability of the authors to properly address the requested changes in their work.

Best regards,

Brunella Bonaccorso

Dear Authors,

we have received the last comments by the two anonymous referees. As you can see, there are still some concerns related to the lack of:
- a clear focus on the specific objectives of the study, compared to the excessive details on the well-established statistical techniques (Referee #3);
- a proper justification of the selected threshold Q90 and a standardization procedure of the runoff indices (Referee #4).

I overall agree with the referees and strongly invite you to take their suggestions properly into account in your final revision. In addition, the introduction still needs some improvements. For instance, the authors still confuse drought, which is a natural phenomenon, with water scarcity, which is due to anthropogenic causes. Therefore, I suggest to delete the following sentences:

LL 35-38: " The main factor involved in hydrological drought is climate change and
anthropogenic activities of surface water resources. The hydrological drought assessment gives a good interpretation of the water surface of the hydrological cycle. Hydrological drought also allows the incorporation of spatial details that impact internal storage and soil, vegetation and terrain characteristics."

LL 46-47: "Drought is most frequently the consequence of climate change and human activities in the particular area or regions."

LL 62-65: "The hydrological drought design system is somewhat complicated and susceptible to catchment characteristics or climate, and a combination of the two variables (Loon et al., 2015; Mohammed and Scholz, 2018; Zhai and Tao, 2017). Precipitation and temperature are two main factors among different environmental factors that mainly determine the climate model and antecedent situation for hydrological drought events (Joetzjer et al., 2013)."

Also, rephrase LL 47-48 as follows: "Human activities and poor management of water resources can lead to water scarcity, which could be exacerbated by drought."

Finally, I have read the revised manuscript and found out that there are still some grammar and language issues. Therefore I recommend checking carefully the manuscript to eliminate errors and to always use the past tense when describing what you attempted and gained.

Some examples are:
L105: replace "where" with "when"
L118: increasing or decreasing?
L234: I suggest "the values of the variables" instead of "the return values"
L396: Delete "objective"
L333: I suggest "have occurred for less than 15 days" and "dependent" instead of "dependable"

I'm looking forward to receiving your revised manuscript for a final decision on its publications.

Best regards,

Brunella Bonaccorso

Dear Authors

I would like to thank you for your effort in dealing with the last minor revisions. I'm now glad to inform you that the paper can be accepted for publication.

Best regards,

Brunella Bonaccorso