Both reviewers agree that the manuscript addresses an important topic and that there is promise in the authors' study; however, there is major revision required to address the review comments. Therefore, I now request that the authors make their proposed changes, in particular paying close attention to satisfying Reviewer 2's comments. The manuscript will then be undergo additional review. Please note that the manuscript still can be rejected after further review. I also ask that the authors ensure the manuscript text, figures and tables comply with the HESS publication guidelines, found here at: http://www.hydrology-and-earth-system-sciences.net/for_authors/manuscript_preparation.html.

Kind regards,
Stacey Archfield

I struggled with a decision on this manuscript. Reviewer #1 has recommended that the manuscript be published in its present form; whereas, the Reviewer #2 rated the manuscript as 'poor' in all categories and recommended continued revision with further review. Reviewer #2 also did not feel their comments were fully responded to and some responses led to additional questions. Despite this, Reviewer #2 does note however, that the manuscript would provide a welcome contribution to the literature if their comments were fully addressed and parts of the manuscript were clarified.

I have carefully read the revised manuscript and agree with the comments of Reviewer #2. Those comments should be addressed as well as the additional comments below. The manuscript will needs to be further revised and will be sent out for additional review comments. Furthermore, the manuscript can still be rejected if there are questions that remain in the next round of revisions.

At this point in the process, I direct the authors to address the comments of Reviewer #2 and also my comments below:

- Are L-moments commonly used to fit the SPEI? If not, please also cite other methods of parameter estimation that are used in the literature. The manuscript also provides no information of the goodness of fit or estimated parameters of the 3-parameter log-logistic for the readers to assess if this were a reasonable assumption or replicate the analysis.

- p. 4, It is not necessary to explain the details of the Mann-Kendall test if the reference is provided. This test is common enough that detailed explanation is not needed. What was the significance level selected for this study? This needs to be noted in the text and Figure 3.

- Section 3.1: The link between this section and the goals of the study are not clearly linked. I understand that they are used to estimate SPEI but there needs to be a more expicit link between this section and the hypotheses tested.

- Also in Section 3.1, many of the differences reported seem quite small (p. 6). The authors need to add more interpretation rather than just spending nearly a page listing the amounts by which the climate variables differ.

- At the end of Section 3.1, there needs to be figure and/or table references to support the statements being made. This is a larger issue with the manuscript that Reviewer #2 also points out - statements need to be backed up by a reference to results or by a citation.

- You repeat the same statement about the Thornwaite approach three times (p. 5, line 35; p. 6, line 20; p. 8, line 38) but offer no reasons for choosing this approach. Also, how might the use of the another estimation method affected the results and conclusions?

- Section 3.2: Again here evidence is needed, particularly in paragraph 1 and last paragraph on p. 7, to support these statements.

- While the study examines 3 reference periods, this is by no means exhaustive. Therefore, I agree with Reviewer #2 that the authors need to be careful to not overstate the conclusions. A much more rigorous testing would examine the effects of sample size and test many different combinations of reference periods to make broader conclusions. As Reviewer #2 stated, the work could still be a useful contribution as it stands - but the conclusions need to be tempered to reflect that only 3 different reference periods were tested and sample size was not evaluated.

- I agree with Reviewer #2 that Section 3.4 offers some nice observations.

- Tables and figures must be stand-alone. They currently do not meet the standards of HESS. Please see http://www.hydrology-and-earth-system-sciences.net/for_authors/manuscript_preparation.html to ensure compliance.

Minor comments:

p. 2, line 3: Do the authors mean only the drought indices noted in the Vicente-Serrano references or all drought indices?

I would like to very much thank the reviewers for their comments on this revised manuscript and the authors for their persistence in accounting for the review comments.

The manuscript has now gone through a second round of revisions. Referee #3 notes that there is still a gap needed to improve the paper for publication; Referee #4 notes that the manuscript should be accepted subject to minor revisions. Both reviewers note - as did the previous reviewers - that the subject of the manuscript and its findings have the potential to make a useful and interesting contribution. It is for this reason that I believe the manuscript should continue in the review process.

I would ask that the authors now respond to the referee comments focusing particularly on the two gaps that are noted - one each by Referee #3 and #4. I will send the manuscript out to for final review to ensure that all comments have been addressed.

I look forward to reviewing the revision.

Kindly,
Stacey

After reading the revised manuscript and the responses to the second-round of peer reviews, I find the manuscript ready to publish subject to some additional technical corrections.

All reviews have noted the promising contribution of this manuscript while offering some important comments to improve the quality of the results, the communication of these results, and the limitations of the analyses, all of which have greatly improved the paper.

I now ask the authors to address these additional technical corrections before final publication:

- p. 1, line 15: Change to "...are used to compute the SPEI: P1 and...."

- Consider whether the regions need to have abbreviations. East Asia, Europe, United States, and West Africa are already short names for these regions and spelling out these names would improve readability so that the reader does have to remember what the abbreviations mean.

- In the conclusions, figures, and tables, Ref1, Ref2, and Ref3 are used but only defined much earlier in the text. Please provide their definition again in these places.

- Figures and tables should be stand-alone, meaning the reader should not have to refer to the text to understand what the abbreviations mean. Please add explanations to each figure and table caption for abbreviated words (abbreviations for units are not necessary).