Thank you for offering an opportunity to review a manuscript that investigated the compound impact of COVID-19 and flood on the mental health of a flood-prone area in Vietnam. The manuscript is well-written and structured, with methodological integrity. However, there are some queries the authors need to address.

Introduction

1. In page 2, line 55, the statement ‘while the flood …… and under-evaluated’ and the following references are misleading, as the authors cited a paper prior to the COVID-19. It would be a good choice if the authors cite Ogunbode et al. (2019) after ‘While the flood impacts on mental health are considerable and long-lasting.’

Otherwise, the Introduction section is well-written, documenting relevant articles in both global and regional contexts.

Methodology

1. The authors clearly documented the simultaneous occurrence of floods and COVID-19 in the selected study areas. They specifically mentioned using the K6 scale to measure distress among the residents of Hue City. Importantly, the K6 scale is designed to assess an individual's mental health, specifically measuring distress experienced over the past 30 days (see Kessler, R. C., Barker, P. R., Colpe, L. J., Epstein, J. F., Gfroerer, J. C., Hiripi, E., . . . Zaslavsky, A. M. (2003). Screening for serious mental illness in the general population. Archives of General Psychiatry, 60(2), 184–189. doi: 10.1001/archpsyc.60.2.184). The authors examined the mental health of residents in Hue City concerning incidents that occurred over two years ago. This raises a question about how they addressed the potential recall bias among participants and whether they considered individuals who may have relocated to study areas after 2022 from other parts of the country. Additionally, the authors did not specify any inclusion or exclusion criteria for the population studied.
2. The authors stated they interviewed 400 household heads using systematic random sampling from two communes; however, it is unclear if this sample size adequately represents the study areas.
3. The authors are requested to mention the reliability of K6 in their study.
4. The authors are requested to provide any relevant articles that support merging 'moderate' and 'severe' distress into the 'Yes' category. If they choose not to merge 'no' and 'moderate' distress into the 'no or moderate' distress category, they must provide an explanation for this decision.

The authors are requested to address or clarify the aforementioned issues in the methodology.

The paper is well-written, presenting a clear and logical structure, which facilitates the reader's understanding.

The language is objective and well-founded, and the methodology is well-defined, with appropriate quantitative methods.

Furthermore, this topic is very relevant, especially in the context of research on multiple risks and public health. The work is interesting and useful for NHESS readers.

Below are some questions and suggestions for the authors:

ABSTRACT

An adequate abstract—please provide a statement explaining the "why" the study was conducted. I believe that explaining the "why" can demonstrate the purpose behind creating conceptual understanding.

INTRODUCTION

Lines 69-98: I suggest moving the initial part of these lines to the methodology section and another part to the results and discussion section.

CASE STUDY AREA

Line 111: Is there any information on the percentage of the country's population that has been or is currently affected by floods?

Line 122: Is it possible to cite historical extreme events that have occurred in the region over the decades? I believe this information is important for understanding the historical context and frequency of floods in the region.

Lines 144-151: I suggest moving this paragraph closer to Figure 1. Are the populations of these two communities representative of the population of Hue City?

METHODS

Line 154: Please briefly explain the tool and include a link to access it. 

Was the collective memory of the community taken into consideration, given that the interviews were conducted years after COVID-19? How might this introduce bias into the respondents' answers? Do the authors consider this factor a limitation of the method?

(Suggested reading for concepts and discussion: https://doi.org/10.1111/jfr3.12679 ; doi.org/10.1002/2017WR022036; https://doi.org/10.3986/AGS49107).

I congratulate the authors on their excellent paper.