Review Reports - Evaluation of Coupled Hydrological–Hydrodynamic Scheme Applicability Under Reservoir Regulation in the Huai River Basin

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Major Comments

1. Incomplete introduction paragraph (Line 19). The final paragraph of the Introduction ends mid-sentence: "Using continuous simulations from 1972 to 1995 and four representative historical flood events in 1991, 2003, 2007, and 2020 (Bi et al., 2004; Xue et al. 2009, Zhang 2021)." This is not a complete sentence. The aim and objectives of the paper appear to be missing. Please complete this paragraph with a clear statement of what the study evaluates and what the paper delivers.

2. Acknowledgements cut off (Line 102). The Acknowledgements section contains only the letters "Th". Please restore the full text.

3. Metric count inconsistency (Line 47). The text states "three standard statistical metrics" but then lists four: NSE, KGE, Pearson Correlation Coefficient, and MBE. Please either correct the count to 4 or remove 1 metric and explain the choice. Additionally, the symbol for the Pearson Correlation Coefficient appears as an empty placeholder "()" in this line, suggesting a rendering issue with the equation. Please check that all variable symbols display correctly throughout the metrics section (Lines 47-54).

4. NSE < 0 at JJJ Station (Line 70). The text notes that in the 2007 simulation at JJJ Station, NSE for water level was < 0 despite a high r value (> 0.88). An NSE below zero means the model performs worse than simply using the observed mean, which is quite poor. This finding is currently noted in passing without explanation. Please provide at least a brief discussion of why this occurs, and whether it affects the conclusions drawn for this station.

5. Citation year mismatches (Lines 17-18). "Fan et al. 2008" is cited in Line 17, but the reference list (Line 108) has Fan Y. et al. as a 2017 paper in Advances in Meteorology. Similarly, "Yin et al. 2000" is cited in Line 18, but the reference list (Line 145) has Yin W. et al. as a 2025 paper. Please verify and correct both.

6. Grammar error in Conclusion (Line 100). "selects efficient models is critical" does not parse correctly. Suggested fix: "selecting appropriate models is critical for accurate flood simulation".

Comments on the Quality of English Language

1. Affiliation typo (Line 3). Reads "uhan Hubei 430000": should be "Wuhan Hubei 430000".

2. Missing space in affiliation (Line 6). "Yangtze River Protection and Green Development Research InstituteNanjing, China" is missing a space and comma between "Institute" and "Nanjing".

3. Subject-verb agreement (Line 31). "This study employs a coupled hydrological-hydrodynamic schemes" should be either "a coupled hydrological-hydrodynamic scheme" (singular) or "coupled hydrological-hydrodynamic schemes" (plural without the article "a").

4. Scheme vs. Scenario inconsistency (Lines 61, 82, 83). "Scheme I/II/III" is used throughout the paper but "Scenario II" and "Scenario III" appear in the Discussion and Results sections. Please use one term consistently throughout. "Scheme" is recommended as it is used in the title.

5. "All scenarios" (Line 61). "While all scenarios successfully simulate low-flow periods" should read "While all schemes successfully simulate low-flow periods", consistent with the terminology used elsewhere.

6. Wordy phrasing (Line 65). "In order to assess the model's efficacy under diverse hydrological conditions, we identified four exemplary flood events" could be simplified to "To evaluate model performance under varied hydrological conditions, four representative flood events were selected". The word "exemplary" is also an unusual choice here; "representative" is more standard.

7. Awkward phrasing (Line 70). "Irrespective of whether NSE or r is taken into consideration" is unnecessarily verbose. Suggested revision: "For both NSE and r, the CaMa-Flood model demonstrated superior performance..."

8. Calibration stopping criterion (Line 45). Stopping calibration at NSE/KGE > 0.6 to avoid overfitting to the Routing model is an unusual but reasonable design choice. Consider adding one sentence explaining the rationale explicitly, as reviewers may question why 0.6 was chosen as the threshold.

9. Water-level paradox needs more discussion (Line 70, Section 4.1). Scheme II sometimes yields more accurate water levels than Scheme III. This is an interesting and non-trivial finding that is currently addressed in only one sentence. A few more sentences on why this might occur (e.g., whether simplified release rules introduce systematic timing offsets, or whether certain reaches or seasons are more affected) would significantly strengthen the Discussion.

10. Incomplete author name in reference (Line 150). "Zhang, J., Y. Review and reflection on China's hydrological forecasting techniques" appears to have an incomplete author name ("Y." with no surname). Please correct this reference entry.

11. Unclosed parenthesis in reference (Line 125). "Nachtergaele, F., H. Van Velthuizen, L. Verelst, et al. (2008. Harmonized World Soil Database" has an unclosed parenthesis: "(2008." should be "(2008)".

12. Duplicate reference (Lines 136-137). Wang et al. (2021), the Lancang-Mekong modelling paper, appears twice in the reference list. Please remove the duplicate.

13. "an mean NSE" (Line 66). Should be "a mean NSE".

14. Reference list formatting. Some entries use full journal names (e.g., Lines 105, 110, 111) while others use abbreviated formats (e.g., Lines 104, 108, 119). MDPI Hydrology uses a numbered reference style. Please standardise the formatting throughout.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript presents a systematic comparison of hydrological and hydrodynamic modeling schemes, incorporating reservoir regulation and levee representation, to evaluate flood simulation performance in a human-regulated basin. The study is methodologically sound and provides useful insights into model applicability under anthropogenic influence. However, substantial shortcomings remain in terms of writing clarity, result synthesis, and the articulation of broader implications. A major revision is therefore required. Specific comments are listed below.

(1) The abstract lacks conciseness and fails to highlight key findings clearly. The current abstract contains overly long sentences and relies heavily on semicolons, which reduces readability. More importantly, the main conclusions (e.g., differences in model performance across river sections and trade-offs between discharge and water level simulation) are not sufficiently emphasized.

(2) The research gap in the Introduction is not sufficiently focused. Although the manuscript provides a comprehensive literature review, it does not clearly define the specific scientific gaps addressed by this study. The necessity of comparing the three modeling schemes is mentioned, but the unresolved contradictions in existing studies remain vague. The authors should explicitly identify 2–3 key gaps.

(3) The study assumes stationarity over a long simulation period without accounting for urbanization-induced hydrological changes. The modeling period spans several decades (e.g., including data from the 1970s), yet the manuscript does not consider the potential impact of land-use change and urbanization on hydrological processes. In rapidly developing basins, urban expansion can significantly alter runoff generation, drainage efficiency, and flood response. Calibrating the model using early-period data under different underlying surface conditions may introduce bias when applied to later periods.

(4) The Results section is data-rich but lacks synthesis and generalization. The presentation of results is largely descriptive, often listing station-by-station performance without extracting overarching patterns. This limits the interpretability of the findings. The authors should summarize the results into a few key insights (e.g., upstream vs. downstream performance differences, discharge vs. water-level trade-offs) and explicitly state general trends rather than only reporting numerical values.

(5) The Discussion lacks generalizable insights and remains case-specific. The discussion provides reasonable explanations for model performance differences but remains largely descriptive and case-oriented. It does not sufficiently elevate the findings to a broader methodological or theoretical level. The authors should extract general principles for model selection in regulated basins, such as the importance of process-oriented modeling and the trade-offs between hydrological and hydrodynamic approaches.

Comments on the Quality of English Language

The manuscript requires substantial improvement in academic wording and terminological precision. While the overall meaning is understandable, the manuscript contains several instances of informal, vague, or imprecise wording that do not meet the standards of academic writing. For example, general terms such as “good performance”, “better results”, or “large differences” are frequently used without quantitative support. In addition, some technical terms (e.g., “flood process”, “simulation effect”) are not standard in hydrological literature and should be replaced with more conventional expressions.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

The authors are optimizing the reservoir at the site under study by modeling its inflows and outflows. Research is provided on comparing the measured (existing) data and the simulation. Models for providing it were carefully selected, given the current state of the art, the lack of resources in this broad and often unthankful topic for analysts, and the complexity of the material. The literature review provides a detailed comparison of the available and related knowledge relevant to the research presented in the paper.

VIC, Routing, CaMa-Flood, and CaMa-Flood models are fitted at the high-quality level. The only lack in the research is that the authors should define and test the dependence of the precipitation on observed and simulated inflows. The correlation between these values will be sufficient to gain insight into the problem. Conclusions will be more robust in this way. Authors should also write a comment about the application of the presented three schemes for other river catchments. Where are the limitations? For example, applications under different hydrogeological conditions, torrential watercourses, etc.?

Authors should enclose a larger map, i.e., a map with a scale that allows the geographical position of China to be determined. Readers outside China may not be familiar with the location under analysis.