General Comments

This paper aims to use isotopic measurements in an extremely arid basin in the northeastern Tibetan Plateau to study the water resources of the area and their responses to climate change. The objective is a worthy one, but not very clearly enunciated. The aim of the research is within the scope of HESS and the paper contributes significant new data and analysis of the results. The conclusions reached are substantial and important, particularly as they are for such a climatically difficult area to research.

The extensive data and scientific methods employed allow the authors to reach well-founded interpretations and conclusions. The conclusions reached are substantial. The methods and assumptions are valid and clearly described. The authors give adequate credit to related work and cite appropriate references.

However, the paper is difficult to read and understand. I think this is partly because: 1) it lacks a clear focus and therefore the paper seems to ramble on without direction (as noted above the objective does not seem clearly enunciated), 2) the language is frequently difficult with often very general terms used (such as “Associated Hydrological Indications” in the title”) instead of more specific terms that would give a clearer picture, or 3) to a less extent the use of combined words (such as “spatiotemporal”, “spatial-seasonal”) makes for difficult reading. Simple words are generally clearer. However, I realise combined words are being increasingly used in scientific papers, and can have specific meanings in some contexts.

A better title might be “Isotopic variations in surface waters and groundwaters of an arid basin and their responses to climate change”.

Specific Comments

1)  The captions to all of the figures need to be more informative. Eg What data does the inset in Fig. 3a show? Also the light lines in Figs. 4 and 5 show distribution patterns in the δ¹⁸O data, but there is no mention of these in the captions. Fig. 11 caption does not identify what is in Figs. 11a and 11b.

2)  I don’t think Fig. 2 is necessary for the paper, although it is interesting.

3)  How is skew defined? The formula used should be explained in Sampling and methods (Sect. 3.) if skew is in fact an important part of the paper. I’m not sure that it is. For example:

L258 The paper states “The basin surface water mean δ¹⁸O and δD values were positively skewed by −0.08‰ to 1.08‰ and 0.63‰ to 10.58‰, respectively, in the wet seasons.” How is this different from “The basin surface water mean δ¹⁸O and δD values were more positive by −0.08‰ to 1.08‰ and 0.63‰ to 10.58‰, respectively, in the wet seasons.”? The latter sentence is much easier to understand (assuming it correctly expresses the intended meaning. If it doesn’t, I don’t know what the original sentence means.)

Again, L614-615 states “The mean values of surface water δ¹⁸O and δD … are negatively skewed from west to east …”. Does this mean that “The mean values of surface water δ¹⁸O and δD … decrease from west to east …”?

Technical Comments

L19 Use of the word “hydrothermal” is not helpful to the reader. Hydrothermal usually refers to water heated by the Earth's internal heat underground, which is not what the writer means.

L137 “Altun fault” not “Alun fault”

L162 “phreatic” not “phrenic”

L178 Should be “the precision was improved to less than ± 0.8 TU” not “more than ± 0.8 TU”.

L499 Should be “fell” not “fall”

普通的留言

This paper aims to reveal the response of hydrological processes to climate change in an extremely arid basin located on the north-eastern Tibetan Plateau, where it is really an ideal area to evaluate hydrological response to climate changes. With the support of large datasets including stable isotopes and water chemical compositions for a whole basin and its around mountains from different spatial-temporal scales, the manuscript has clarified the entire water cycle processes as well as the isotope hydrology responses to rapid climate changes in an extremely arid basin in the Tibetan Plateau. In addition, the manuscript has also concluded a perspective on the variation trends of water resources under the condition of multiple water sources recharge and climate warming. As my assessment, the topic about the impact of climate change on water resources talked in this manuscript is a general global focused issue. The research objectives, methodology, content and scientific hypotheses of this manuscript are well coincided within the scope of HESS. Thus, I suggest to accept this manuscript, after somewhat improvements. My main concerns are as follows:

1. The title needs to be reconsidered. A title with a clear direction would help to highlight the topic. I believe that the authors may want to emphasize the response of surface water and groundwater isotope variations to climate change. In addition, some of the sub-headings in the text should be also reconsidered so that they can outline the content of the text.

1. It seems to me that the abstract and introduction need to be furtherly condensed. Although the article is now look -like systematic, a more focused topic is the key to attract the reader's attention.

1. As for the text structure, it seems to be a bit confused and may be necessary adjusted. For example, the Section 4.1 should to be better to move after Sections 4.2 and 4.3. It seems to be too long for section 5.1, some subheadings may be added in order to help to fill the gap for readers. Section 5.3 is mainly focused on the groundwater circulation mechanism, which in my view, it should be moved to section 5.2. In addition to the overall structure, the content between paragraphs also needs to be sorted out. Example, the second paragraph of section 5.4 is too long and includes too many ideas. It should be rewritten to be more in point or logical.

1. Some Figures need to be rehearsed, e.g., regarding Figure 2, a hydrogeological map may be more appropriate for the topic of the paper rather than a simplified tectonic map. In addition, detail information needs to be added in some figure captions.

Some minor shortcomings please consider to improve:

Lines 13-14: Delete “The surface water heavy isotopes enrich during the wet season and deplete during the dry season”. The abstract should highlight key findings.

Line 19: hydrothermal conditions are not an appropriate terminology, I guess the author wants to express temperature and precipitation regimes.

Line 21: Delete "ice/snow".

Line 28 Keywords should be ordered according to major and second categories and then followed specific research directions

Line 37：Delete "region of the".

Line 57: “These issues require an in-depth investigation” is a repetition of the “several questions remain to be resolved” in Line 55.

Lines 91-95: No more than 3 goals of the study were considered reasonable. The authors were advised to streamline the study objectives. The order of the research objectives should also be expressed more logical.

Line 118: “Hydrogeology and structure” can be changed to Basic hydrogeological setting

Line 137: Altun is not Alun

Line 162: phreatic groundwater is not phrenic groundwater

Line 206: Section 4.1 seems to duplicate 4.2 and 4.3 in terms of structure, although the contents are different. I think the contents of 4.1 can be moved after 4.2 and 4.3 after simplification.

Line 245: Specific terminology in the whole text should be used, e.g.“positively skewed” is not a terminology and it easily causes ambiguity. For isotopic expression, please use “depleted or enriched” to decipher their variations.

Line 254: “seasonal and spatial variations” should be replaced by “spatial and seasonal variations”.

Line 263-268: The description of spatial variations should be placed before the description of temporal variations in order to match the title.

Line 292: In chapter 5.1, some subheadings need to be added. Also, the order of the paragraphs should be logically adjusted. The paragraph on moisture tracing should be placed previously, and the content of Lines 309-330 should be swapped with Lines 356-376.

Line 377: please revise it as Line 254.

第378行：据我了解，区域增暖增湿趋势优于该地区暖湿程度

第 386 行：第 5.2 章的标题和副标题也需要重新考虑以总结该段落的主题。另外，本章应加强文章的主旨，但应缩短或删除一些与科学问题不密切相关的讨论。

第394行：5.2.1在极度干旱地区，降水补给主要发生在雨季，这是一个一般概念，无需强调。

第445行：请作者确认一下“不同季节”是正确的吗？我认为作者指的是不同的阶段。

第 502-504 行：这些句子可以删除，以便在结果部分中重复。

第 651-562 行：这是前一句的重复。

第599行：虽然图10b提供了大量数据，但它是多余的，因为图10a足以显示研究区域显着的气候变化趋势。它也可以从文本中删除，因为不提倡明显的信息冗余。

第604行：作者应该报告图11中数据的来源。因为有些数据显然是从文献中收集的。我建议将图 11 放在附件中，因为图 12 中已经显示了本节的重点内容。

Due to an unknown error, the previous comment titled "RC2:'Comment on hess-2023-67'" did not contain all the correct content, here are my full comments.

General comments

This paper aims to reveal the response of hydrological processes to climate change in an extremely arid basin located on the north-eastern Tibetan Plateau, where it is really an ideal area to evaluate hydrological response to climate changes. With the support of large datasets including stable isotopes and water chemical compositions for a whole basin and its around mountains from different spatial-temporal scales, the manuscript has clarified the entire water cycle processes as well as the isotope hydrology responses to rapid climate changes in an extremely arid basin in the Tibetan Plateau. In addition, the manuscript has also concluded a perspective on the variation trends of water resources under the condition of multiple water sources recharge and climate warming. As my assessment, the topic about the impact of climate change on water resources talked in this manuscript is a general global focused issue. The research objectives, methodology, content and scientific hypotheses of this manuscript are well coincided within the scope of HESS. Thus, I suggest to accept this manuscript, after somewhat improvements. My main concerns are as follows:

1. The title needs to be reconsidered. A title with a clear direction would help to highlight the topic. I believe that the authors may want to emphasize the response of surface water and groundwater isotope variations to climate change. In addition, some of the sub-headings in the text should be also reconsidered so that they can outline the content of the text.
2. It seems to me that the abstract and introduction need to be furtherly condensed. Although the article is now look -like systematic, a more focused topic is the key to attract the reader's attention.
3. As for the text structure, it seems to be a bit confused and may be necessary adjusted. For example, the Section 4.1 should to be better to move after Sections 4.2 and 4.3. It seems to be too long for section 5.1, some subheadings may be added in order to help to fill the gap for readers. Section 5.3 is mainly focused on the groundwater circulation mechanism, which in my view, it should be moved to section 5.2. In addition to the overall structure, the content between paragraphs also needs to be sorted out. Example, the second paragraph of section 5.4 is too long and includes too many ideas. It should be rewritten to be more in point or logical.
4. Some Figures need to be rehearsed, e.g., regarding Figure 2, a hydrogeological map may be more appropriate for the topic of the paper rather than a simplified tectonic map. In addition, detail information needs to be added in some figure captions.

Some minor shortcomings please consider to improve:

Lines 13-14: Delete “The surface water heavy isotopes enrich during the wet season and deplete during the dry season”. The abstract should highlight key findings.

Line 19: hydrothermal conditions are not an appropriate terminology, I guess the author wants to express temperature and precipitation regimes.

Line 21: Delete "ice/snow".

Line 28: Keywords should be ordered according to major and second categories and then followed specific research directions

Line 37：Delete "region of the".

Line 57: “These issues require an in-depth investigation” is a repetition of the “several questions remain to be resolved” in Line 55.

Lines 91-95: No more than 3 goals of the study were considered reasonable. The authors were advised to streamline the study objectives. The order of the research objectives should also be expressed more logical.

Line 118: “Hydrogeology and structure” can be changed to Basic hydrogeological setting

Line 137: Altun is not Alun

Line 162: phreatic groundwater is not phrenic groundwater

Line 206: Section 4.1 seems to duplicate 4.2 and 4.3 in terms of structure, although the contents are different. I think the contents of 4.1 can be moved after 4.2 and 4.3 after simplification.

Line 245: Specific terminology in the whole text should be used, e.g.“positively skewed” is not a terminology and it easily causes ambiguity. For isotopic expression, please use “depleted or enriched” to decipher their variations.

Line 254: “seasonal and spatial variations” should be replaced by “spatial and seasonal variations”.

Line 263-268: The description of spatial variations should be placed before the description of temporal variations in order to match the title.

Line 292: In chapter 5.1, some subheadings need to be added. Also, the order of the paragraphs should be logically adjusted. The paragraph on moisture tracing should be placed previously, and the content of Lines 309-330 should be swapped with Lines 356-376.

Line 377: please revise it as Line 254.

Line 378: According to my understanding, regional warming and humidification trends is better than the extent of warmth and humidity in the region

Line 386: The headings and subheadings of chapter 5.2 also need to be reconsidered to summarize the topic of the paragraph. Additionally, in this chapter, the main idea of the article should be strengthened but some discussions that are not closely related to the scientific issues should be shorten or deleted.

Line 394: 5.2.1 In the extremely arid region, recharge from precipitation occurs mainly during the wet season, which is a general idea and need not to be emphasized.

Line 445: Can the authors please confirm that it is different seasons that is correct? I think the author meant different phases.

Lines 502-504: These sentences can be deleted for repetition in the result section.

Lines 651-562: This is a repetition of the previous sentence.

Line 599: Figure 10b is redundant, although it presents a lot of data, as Figure 10a is sufficient to show the striking climate change trends in the study area. It could also be removed from the text, as the obvious redundancy of information is not advocated.

Line 604: The authors should report the source of the data in Figure 11. Because some of the data are obviously collected from the literature. I would suggest putting figure 11 in the annex as the highlights of this section are already shown in Figure 12.

This paper combines a very rich dataset of water isotopologues to provide conceptual models of the continental water cycle components in the different parts of the extensive, arid Qaidam basin in the Tibetan Plateau. The authors reach interesting conclusions on constrasting functioning of the sources and fates of water pathways and surface-groundwater exchanges in different part of the study area, with important implications for ongoing and future trajectories in a changing climate.

While this could be a significant contribution to the community and the topic fit wells in HESS readership, in my view the manuscript suffers from an inadapted structure that makes it hard to follow, and to fully assess the soundness of the proposed analyses and discussions. Due to this and other issues, I recommend a very substantial rewriting effort before this manuscript can be considered for publication. This would include a further effort on the level of written english as well ; I tried to list some items in the technical comments, but this is not the role of a reviewer and a complete proof-reading, if possible by a native speaker, will be needed.



General comments

The current structure of paper seems to be the biggest issue at this stage. On this matter I concur with the other comments, who notably summarized the main issues: lack of clear focus, difficult vocabulary and formulations (in the main text and some titles).

In particular, it seems the Discussion section is too long and essentially mixes a lot of additional results and discussion. I strongly advise the authors to rework this section in connexion with the Results section. Given the number of datasets and related analysis presented, special care should be given in crafting a more precise focus and red thread throughout these sections, in connexion with more clearly stated objectives and research questions.

Specific comments

L20: "caused by climate warming" during which period?

L22: what are "structural channels"?

L29-30: I disagree that an "in-depth study of the hydrological cycle is a prerequisite of water management" ; Effective water management practice implementation may be hindered not by lack of knowledge but also geopolitical reasons, although it is a case-by-case matter. I understand the authors need to justify the signficance of their study, so I'd recommand to be more balanced, for example rephrasing as follows "an in-depth study of the hydrological cycle processes is a prerequisite for accurate trend forecasting, and helps to design efficient water resource management strategies."

L62: H & O are not isotopes per sé. May an appropriate formulation would be "The isotopes of hydrogen and oxygen elements are useful tracers of the water cycle..."

L66-68: why talking only about stable isotopes (excluding 3H), and then mentioning 3H in the next sentence? Both stable and non-stable types are useful tracers in the applications cited.

L70-71: an additional references using stable istopes and tritium may be Rodriguez et al. (2019) and a recent paper on the topic (Benettin et al., 2022)

L81: I'm not sure to understand how tectonic patterns are caused by "hydrological, climatic and hydrogeological conditions". Isn't the other way around?

L91-95: objectives #1 to #2 seem somewhat vague and overlap. Also, perhaps the authors should consider having more focus objective than #3, e.g. instead of tracking "the entire water cycle" --> "identying and quantifying the main components of the regional cycle, their timing and spatial heterogeneity" might be already quite ambitious and enough?

L96-100: This part is essentially a repetition of the above, please consider removing it.

L159: is the the sampling frequency or sampling period?

L163-164: Providing a quick idea of the rain and snow(melt) sampling frequency would be useful.

L230: I guess mentioning "evaporative fractionation" instead of "evaporation" helps for the analysis the plotting below the LMWL

L253: In this section, having a dual-isotopes plots per locations (possibly in the supplmentary materials) would help the analysis; it seems this the current FIg. 7, but why does the latter comes much latter and is being only quickly mentioned in the main text (L357, L393) ?

L285-288: I am not convinced that this assertion is supported by the data. Can the authors further develop and articulate this hyptohesis?

L337-340: This is interesting and should probably come earlier in the analysis, at least before general statements as those found e.g. L328-330?

L351-352: Is 3 permill a substantial (from 10 to 7) a substantial differences in d-excess?

L400-519: In line with the general comments, it seems quite strange that the information content and results of tritium analysis only appears so late in the paper.

L499: Typical tritium detection limit is around 0.05 TU or less, so this gives considerable range from "<3TU". Could the authors explain why they grouped all samples below 3TU and those "below detection limit"? And also provide their detection limit somewhere in the methods?

L578: what do the authors mean by "the cyclical nature of climate change" ? The long-term glacial-interglacial dynamics? Please rephrase, as it reads it may be understood that current global warming is cyclical (against all evidence synthetized by the IPCC).

L587-589: I did not understand how the authors can predict a large-scale decrease after the increase in water resources, please clarify.

L592-593: does this involve regional evaporation recycling mechanisms? AS it stands, little of this is directly discuss in the paper, yet it seems like an important piece of the puzzle.

L637: similar comment as for L578 ("cyclical nature of climate change")

Technical comments

L8: "climate warming" reads odd to me. maybe "climate change" or "global warming" instead? It is found several times in the manuscript

L13: heavy isotopes do not enrich, more correctly stated "the water is enriched in heavy isotopes"

L18: "regulated" reads strange; "controlled", maybe?

L22: what is the "impending climate change process"? Perhaps "In the face of ongoing environmental changes, ..."

L47: replace "and a substantial steep...globally" by "with a steep rise in temperature overall".

L49: "0.53°C per decade"?

L77: please define a "confined regional unit scale" or rephrase.

L84: "to study the entire process of the water cycle" --> "to get a comprehensive view of the water cycle"?

L85: "isotopic composition" rather than "isotopes"

L92: "in this alpine arid basin"

L131: "extensive" instead of "expansive"?

L162: I am not sure what "phrenic" means here; is it "phreatic"?

L245: by "positively skewed" I guess the authors mean that it is more enriched ; I find the latter expression more correct and self-explanatory.

L29 - Fig. 3: the figure is very small and symbols are hard to tease out ; consider using a larger, vertically stacked figure (with higher DPI / less compression as well, it is quite pixelized at present)

L313: what do the authors mean by "an augmentation in the continental characteristics of water vapor"? Please clarify and/or rephrase.

L457 - Fig. 8: The scale is hard to read ; I suggest the authors remove the color from the background (with a simplified map) and use a color scale to isotopic ratios and 3H. I would also suggest to duplicate the panels to clearly separate surface and groundwater, as surface is here only shown for tritium.

References

• Benettin, P., Rodriguez, N. B., Sprenger, M., Kim, M., Klaus, J., Harman, C. J., ... & McDonnell, J. J. (2022). Transit time estimation in catchments: Recent developments and future directions. Water Resources Research, 58(11), e2022WR033096.
• Rodriguez, N. B., Pfister, L., Zehe, E., & Klaus, J. (2021). A comparison of catchment travel times and storage deduced from deuterium and tritium tracers using StorAge Selection functions. Hydrology and Earth System Sciences, 25(1), 401-428.