The paper presents some of the first insights into compound flooding in the Mekong Delta. By providing a range of scenarios, including variations in discharge, storm surge, lowering of the riverbed and integration of (extraction-induced) land subsidence and sea-level rise, the authors aim to attribute modelled inundation to the drivers investigated. They conclude that relative sea-level rise (i.e. land subsidence and absolute sea-level rise) constitutes the most to increase inundation in the delta.

We think this paper addresses a so far huge research gap and can make a significant contribution to the advancement of exposure and risk assessment in the Mekong Delta and the investigation of compound flooding and their local specific characteristics. However, we found some critical aspects that have not been touched by the authors but which are necessary to be at least discussed if they cannot be considered in the processing. We briefly address the major points by listing them as follows and also provide a section-wise feedback:

Details and references to the datasets used are missing. The datasets and their quality also need to be reflected in the discussion section.

• The assessment heavily relies on the use of a local elevation model but the DEM details are not provided – only the source – how is the DEM acquired, is it a DSM or a DTM? What is vertical accuracy? What are the artifacts (e.g. blocks) in the elevation model that are very visible in the results? What is the influence of these uncertainties/error on the final outcomes of this study? How does the DEM relate to other DEMs/ground truth data on elevation in the delta?
• The DEM used was based on data from 2008 – how was this combined with the sea level and the land subsidence data? These should also be computed starting in 2008 – as both processes effectively change the relative elevation of the delta plain.
• Reference for the gauge data is missing and should be provided.
• LULC details / references are not provided and should be briefly summarised or at least provided by adding a reference.
• Details on roughness are missing. Was it a single value? Were the initial roughness value(s) determined based on the land-use land cover map? Please provide some more information.
• The paper uses a quantification of ‘Delta subsidence’ while based from the description this is based on a groundwater model however the paper doesn’t reference the original model source (i.e. Minderhoud et al., 2017), which is required as this holds the assumption and also shortcomings of the modelling approach. It is important to note that the modelling results only provide land subsidence following groundwater extraction and not includes other components of land subsidence – this should be made explicit in the result presentation (e.g. change delta subsidence to extraction-induced subsidence) and discussion on the other components not included in the assessment. For this also other literature specifically on land subsidence in Ca Mau on the other components and local measurements can be used: e.g. Zoccarato et al., 2018 (10.1038/s41598-018-29734-7), Karlsrud et al., 2020 (10.5194/piahs-382-111-2020), de Wit et al., 2021 (10.3390/rs13020189). Also Nguyen et al., 2023 (10.1016/j.ecss.2023.108259) provides a valuable comparison with water level measurements to discussed in this study.
• Coastal erosion and shoreline change are included in discussion while happening in the coastal zone – especially with inundations projected up to 2 meter. Please include this in the discussion (e.g. Anthony et al., 2015)
• In addition to elevation loss following land subsidence and SLR – the accretion of sediment should be discussed – as this may cause a positive elevation change. Especially with high flood/inundation with water - sedimentation dynamics will change and therefore elevation – which in turn changes the inundation depth. The lead author has experience in flood plain sedimentation and adding these dynamics in the discussion would strengthen the changes and future dynamics the paper aims to evaluate.
• The discussion section is very short and in its current version is missing several aspects that require critical reflection. We suggest to insert a subsection where the quality of underlying datasets as well as the limitations are discussed. And include a second subsection to discuss implications of your modelling results for the delta’s future and its development/management. Only a very limited number of mitigation and adaptation measures is discussed (i.e. tidal barriers) and these are hardly suitable to tackle the causes and drivers of compound flooding as well as sustaining mangrove ecosystems. Thus can be improved by restricting the discussion.

Minor comments:

Introduction

• 18: there is no “natural disaster”, please delete “natural”.
• 40-41: “Sand dredging rise” sounds a bit strange. Replace it by “increased sand mining”.
• 70: “Vertical sinking” sounds a bit strange. Remove “vertical”.
• 74: Please cite and acknowledge the required source publications of the NASA SLR projection tool, i.e. Fox-Kemper et al. (2021) and the data works of Garner et al. Please check this throughout the entire manuscript.
• 86-90: Please provide references.
• 93: Vulnerability has not been adequately addressed so far. The previous paragraphs were all about future trends and increasing exposure. Please insert a few lines that underpin your statement of increased vulnerability (i.e., studies focussing on societal aspects) or do not call it vulnerability.
• 99-101: Can you provide a reference who will consider it? MONRE, etc.?
• 111: There is no reference made to figure 1 in the text. Either integrate it into the text (for example if you use it to validate your model) or remove it.

Methods

• 129-130: Similar as reference is provided for monsoon precipitation, please also provide a reference when information on elevation above mean sea level is given.
• 145: Provide a reference for the land-use data used.
• 158-159: Provide year of datum establishment in brackets or provide reference where this information is entailed.
• 159-162: More details on the DEM are needed. How was it acquired? Airborne LiDAR? Is it a DSM or a DTM? This information is very important as it has crucial impacts on your model results.
• 163-164: Provide a reference for the gauge data used.
• 185-186: What are the roughness values used? Were the initial roughness values determined based on LULC data?

Results

• 340: Use singular (“scenario”) and not plural.
• 312-429: Could the observation that extraction-induced land subsidence and SLR result in the max. increase of inundation extent and depth also relate to the fact that the underlying data considered provide projections for the longest time scales? This potential should be discussed in the discussion section.
• 402-405: Why are the 4a and 4b scenarios missing in figure 5? Please add them.
• 406-408: The artefacts of the underlying DEM dataset become clearly visible in figure 6. This should be discussed in the discussion section.
• 419-420: The artefacts of the underlying DEM dataset become visible. Seems like as if there are also interpolation (?) artefacts in the scenarios because they look quite strange (esp. S5_b, S4_a). Please check and at least include a paragraph in the discussion section.

Discussion

• 430-472: The discussion section is too short and in its current version is missing several aspects that require critical reflection. Please insert a subsection where the quality of underlying datasets as well as the limitations are discussed. This relates mainly to the DEM and land subsidence data used but may also go beyond.
• 450-452: When adaptation and mitigation strategies are discussed, not only tidal barriers should be mentioned. What about other solutions such as sedimentation strategies that tackle the cause (i.e. elevation loss due to land subsidence)?
• 453-458: The problem of groundwater overexploitation is not discussed at all but needs to be addressed as it is the main driver of land subsidence in the region. Note that the datasets that were used to simulate scenarios S4a and S4b only consider extraction-induced land subsidence but not the total subsidence.
• 459-466: As the implementation of infrastructure adds new load on the deltaic land surface, land subsidence will increase in that area. Please add this comment when the construction of the North-South Expressway is raised.
• 471-472: The implementation only of the measures mentioned in this discussion does not allow for this conclusion as they rather tackle symptoms than the causes. Measures that tackle subsidence-induced elevation loss need to be discussed.

Conclusions

• 475: It is exposure, not vulnerability as this study does not include any social or socio-economic data.
• 483-485: Consider previous comments on the doubled consideration of land subsidence in the combined scenarios as SLR projections from the NASA SLR projection tool include a VLM component.
• 500-505: Note that the adaptation measures listed here do not address the cause and whether the mangrove ecosystem can be sustained in the future.