This study highlighted the influences of hydrometeorological factors on river water isotopes, with their effort on the long-term sampling with relatively high frequency (daily for precipitation samples and hydrometeorological factors and 5-day interval for river water spinning 13 years) and the detailed statistical interpretation, the authors identified the relationship between the hydrometeorological factors and the stable isotopes in river water. For instance, the changes in the river water isotopes are strongly influenced by the corresponding precipitation, evaporation, and runoff discharge, while the river water isotope signals may record the input of heavy and depleted precipitation input and extreme drought events. Moreover, this study found that the most depleted and enriched river water isotopes were controlled by the seasonality of precipitation isotopes and the basin wetness conditions. These findings were revealed based on the 13-year observations in the Xiangjiang River basin, which is a typical basin located in the East Asian monsoon region. Therefore, the results of this study help achieve a better understanding of the seasonal variation and influence factors of the river water isotopes, which may be a very meaningful implication for the water cycle processes and paleoclimate reconstruction in the East Asian monsoon regions. I think this is a relatively well-constructed paper that presents interesting data and reasonable analysis, thus could make a nice contribution and be of interest to many different groups ranging from hydrologists to meteorologists or even paleo-climatologist. Overall, I have some issues that need to be taken into consideration by the authors to help improve their manuscript, while this manuscript could be acceptable for publication in the Hydrology and Earth System Sciences with some moderate revisions.

My specific concerns are:

I notice that the authors have published two papers that focused on the Xiangjiang River water, that is, Xiao (2022a), which used the periodic regression model to estimate the young water fraction, the mean residence time and the seasonal origin of the river water; Xiao et al. (2023) entitled “Identifying river water sources using end-member mixing analysis in a subtropical monsoon basin China”, which used the end-member mixing analysis and water chemistry information to estimate the water sources of the Xiangjiang River that origins from different flow pathways. I suggest discussing and linking more with these existing results and published papers in the discussion section of this paper.

Line 9-35: The authors have done a very good job of identifying the relationship between the precipitation partition and precipitation during different time intervals. Please mention these time intervals in the abstract.

Line 125: Please include specific (and relevant) information in the current manuscript (about sample collection), do not just refer to additional work.

Line 128-133: Why was the sampling interval 5 days? Just for logistics or was there a reason? Daily sampling is indeed challenging but is there a reason for the selection of 5 days? Depending on the precipitation amount and intensity, this 5-day sample interval likely leads to a dampening of the signal (e.g., from precipitation to the river).

Line 143-144: Were snow samples collected off the ground or in a collector? How long after the event were they collected?

Fig. 2: The river water showed abnormally depleted signals during the summer of 2013 and 2017, while the most enriched signals of the river water isotopes occurred in the spring of 2014, what causes these? Have you mentioned or explained these extremum signals?

It is stated that because the variation of d¹⁸O and d²H were similar in the river water and precipitation, only the d²H values are discussed. Generally, just looking at d¹⁸O or d²H will present a different parameter than combining them in some way. Further, the very next section explains how the bi-variate plot and water line (Figure 3) are used in the analyses, which use both d¹⁸O and d²H. What analyses only use d²H and why?

Line 155-160: An important aspect that puzzles me, conceptually speaking, is why no chemistry information was considered in the analysis. Even Electric conductivity or pH. Is that there were no data? Please address.

In the correlations between the influence factors and river water isotopes, some relationships showed non-significant correlations, that is, p > 0.05, I strongly suggest the authors redo the statistical analysis and find the correlations with p > 0.05 and p < 0.1 because that means there is still some degree of the positive or negative correlations although non-statistically significant was found.

The authors talk about the runoff discharge data of the river. However, discharge data are not used in the analyses. Instead, runoff depth (mm) is used (e.g., Figure 8). If discharge data are available, why weren’t they used here? This likely would not change the relationships much, but they would be more useful to see here. Especially as the paper is talking about the influences of river discharges on river water isotopes. Why are the discharge values explained, but not used?

Although the manuscript is generally well-written, it could benefit from thorough proofreading to fix some grammatical errors and typos. I will not list all instances here, but the authors should go through the manuscript carefully to make sure there are no grammatical errors or typos.

Section 5.1 and 5.2: The discussion is very detailed on the environmental significance of the results obtained by the detailed statistical interpretation and well synthesize/integrate their findings with the existing findings from literature from other regions. Especially, the discussion on the potential influence of extreme precipitation or drought events on the river water isotopes and the downstream lakes will be an interesting read for the Hydrology audience.

Section 5.3: In my reading process, I have always had a question, that is, the collection of precipitation samples and the observation of meteorological factors were carried out in Changsha site, while the analysis done in this paper is on the Xiangjiang River basin scale. Whether the sampling at the study site can represent the basin scale with large area has always been a problem in hydrology research, that is, downscaling or upscaling. I think this section solves this question well, at least the analysis in this paper is based on a relatively reliable basis, which may be related to the fact that the Xiangjiang River Basin as a whole is located in the subtropical zone of the southern China, which makes the meteorological elements (precipitation, evaporation, temperature) of the basin have a certain consistency.

Moreover, the precipitation isotope of the basin also has a high correlation, which can be attributed to the similar water vapor source, precipitation form and atmospheric circulation form with the Xiangjiang River basin. I think this and the previous comment should be described and supplemented where appropriate in the manuscript.

These are some places in the discussion section I would have liked to see statements backed by figure references and/or citations. Please go through the manuscript and improve the literature citations of this paper.

Line 509-511: Is this a new finding by this study or it is already known from the literature?

This study entitled “Seasonal Variation And Influence Factors Of River 1 Water Isotopes In The East Asian Monsoon Region: A Case Study In Xiangjiang River Basin Spanning 13 Hydrological Years” reported the significant seasonal variation of River water δ²H (δ²H_R) with the most positive and negative δ2 HR occurring in the spring flood period and summer drought, respectively, and generally aligned with those observed in precipitation. I found that the manuscript is interesting, and the work presented here justifies the title and objective of this research. It is therefore valuable to be published in the Journal of Hydrology and Earth System Sciences (HESS). However, a few things need to be modified before the manuscript can be revised to be accepted in HESS.

• Abstract needs to modify: the abstract should contain Objectives, Methods/Analysis, Findings, and Novelty /Improvement.
• In the introduction, it would strengthen the argument on the methodology if it would be clearly stated what is innovative about this specific methodological development.
• In line with the latter, also balance and articulation of the methodological approach needs to be improved so that the application can be actually demonstrative of the validity of the methodology.
• Please make sure your conclusions section underscores the scientific value added to your paper, and/or the applicability of your findings/results, as indicated previously. Please revise your conclusion part into more detail. Basically, you should enhance your contributions, and limitations, underscore the scientific value added to your paper, and/or the applicability of your findings/results and future study in this session.

That is all from my side, I would recommend this paper, to be published in HESS with all the above-mentioned revisions.

Dear Editor

Thank you very much for considering me as a reviewer for this manuscript. It is an honour for me. Looking forward to act as a reviewer for more publications in your respected journal.

Regards

Dr. Faizan ur Rehman Qaiser

1. Is this topic of general interest?

yes

1. Does this article contain new aspects?

yes

1. Does the presentation reflect the present state of knowledge?

No, not at all

1. Are all relevant aspects of the topic presented fully?

yes

1. Is the literature sufficiently critical, current, and internationally evaluated?

yes

1. Is the size of the article appropriate to the contents?

yes

1. Is the text presented in a manner that scientists in other disciplines will understand?

yes

1. Is the text presented and arranged clearly and concisely?

yes

1. Does the abstract appropriately cover the contents of the article?

yes

1. Are the keywords suitable so that the article can again be found in the current registers or indexes?

yes

1. Have the conclusions been justified sufficiently?

yes

1. Does the title appropriately reflect the contents of the paper?

yes