Applicability of Difference in Oxygen-18 and Deuterium of Water Sources and Isotopic Hydrograph Separation in a Bamboo Catchment during Different Rainfall Types

Round 1

Reviewer 1 Report

The manuscript presented some important high resolution stable water isotope data in the lower reach of Yangtze River, China. The authors measured stable isotopes in rainwater, throughfall, groundwater, stream water, soil water etc. for hydrograph separation in a bamboo watershed during two important monsoon events viz., typhoon and plam rain.

Some major issues to be rectified before accepting the manuscript for publication as listed below:

The presentation and English language need improvement

The methods used for hydrograph separation in the sub-sections of 3.2 are not clear. Authors should clearly mention what are the mixing models used for the estimations in these sections and what are end-member isotopic values.

The abstract does not provide any important information. Please rewrite it in such a way that someone should get an overview of the findings of the study. For example, it is impossible to understand by a reader what authors mean by the following sentences unless he/she reads the full paper.

‘However, the variation in soil water isotopic composition remains largely uncertain. High temporal resolution rainfall δ¹⁸O data during a storm event in isotopic hydrograph separation allowed us to detect a short-lived reversal in the pre-event water fraction, which was observed in the rising limb of discharge.’  

In section 3.2 authors used two component mixing for hydrograph separation and the components are pre-event and event waters. Probably authors assumed groundwater, soil water, surface water etc. as one component and direct rainfall as another component. It is not clear what are the implications of separating pre-event and event rains.

In section 3.2.2 it is not clear how contribution to pre-event rain from rainfall and throughfall are estimated (the scales for the % pre-event water by rain and throughfall are not given).  

In section 3.2.3 and Table 4 authors separately estimated the contributions of surface, soil and groundwater in what in the pre-event water or in the streamflow?

Line 495-509: from the discussion in this paragraph, it seems authors estimated surface water, groundwater and soil water in the streamflow during the two rainfall events but it is not clear what is surface water here. Is it the combined water from pre-event, rainfall and throughfall?

The conclusion section need to be re-written removing unnecessary discussion.

Specific comments

Line 21: Please mention what isotopic compositions? Suggestion: Stable isotopic compositions (δ¹⁸O and δD) in different …..

Line 24: mention the name of the study area after ‘river water isotopic composition…’

Line 25: difference in variation in δ¹⁸O and δD in event-scale samples….

Line 47: There has been some works on response of the hydrological cycle due to climate change and land-use/land-cover change….

Line 134: Figure 1 is not given anywhere in the manuscript.

Figure 3: No δ²H data presented in the figure as mentioned in the caption.

Figure 4: Instead of naming individual symbols, authors could show them as a legend. Also best fit lines could be drawn for the individual datasets, e.g., a line for the soil water. The slope and intercepts would help to understand various secondary processes responsible for the deviation from LMWL and GMWL.

Figure 5: Again use legends corresponding to different symbols. In Figure 5c and 5d, the scale for % event water is not shown.

Line 312: … on of the sources of recharge to the river water

Line 324, 328: remove ‘depth’

Line 388: please elaborate what do you mean by intense dynamic fractionation

Line 549-561: these are not conclusions, please remove. Also remove unnecessary discussion from the conclusion section and if required include them in discussion.

Author Response

1. The presentation and English language need improvement

Response: We have rewritten some parts of the paper and asked PhD in USA to help us for English writing and editing.

2. The methods used for hydrograph separation in the sub-sections of 3.2 are not clear. Authors should clearly mention what are the mixing models used for the estimations in these sections and what are end-member isotopic values.

Response: We have added the explanation in section 2.2.2 Hydrograph separation method.

As “The stable oxygen and hydrogen isotopes were used in the two-source mixing model (one is event water, usually refers to rainfall; the other is pre-event water, usually refers to groundwater and soil water, which stored in watershed prior to the event) to determine the relative inputs to stream discharge from pre-event and event water.”

Usually, the end-members of two-source mixing model are rainfall (event water, new water) and groundwater (pre-event water, old water) and that of three-component model are rainfall, soil water and groundwater.

3. The abstract does not provide any important information. Please rewrite it in such a way that someone should get an overview of the findings of the study. For example, it is impossible to understand by a reader what authors mean by the following sentences unless he/she reads the full paper.

‘However, the variation in soil water isotopic composition remains largely uncertain. High temporal resolution rainfall δ18O data during a storm event in isotopic hydrograph separation allowed us to detect a short-lived reversal in the pre-event water fraction, which was observed in the rising limb of discharge.’  

Response: We have rewritten the whole abstract part.

As “Typhoon storm and plum rain are two typical precipitation events in the middle and lower reached of the Yangtze River, which are easy to form flood disasters. Using the stable isotopic composition difference of different water sources to separate the discharge hydrograph is helpful to better understand the runoff generation and concentration processes of the two typical rainfall events. We selected a typical typhoon storm and plum rain occurred in 2016 in a small bamboo forest watershed in the lower reaches of the Yangtze River and investigated the temporal variation of rainfall, throughfall, surface water, soil water, groundwater and river water isotopic composition in these two rainfall events for the following purposes: (1) to quantify the difference in variation in and δ¹⁸O and δD in event-scale samples between different rainfall types, (2) to evaluate how the differences between rainfall and throughfall isotopic composition and different rainfall types affect hydrograph separation, and (3) to determine the proportion of soil water in the discharge hydrograph during different rainfall types. The results show that the variation range of rainfall δ¹⁸O was 3.7‰ in the typhoon and 5.2‰ in the plum rain, which were larger than that of throughfall, surface water, groundwater and river water and less than that of soil water. However, due to the influence of different soil water extraction methods, the variation range of soil water isotope composition has great uncertainty. Whether the temporal change of rainfall isotope is considered have a large impact on the hydrograph separation. If the temporal change of rainfall isotope is considered, the three stages of the change of event water proportion in the rising stage of discharge can be obviously observed. However, without considering the temporal change of rainfall isotope, the three stage of event water proportion cannot be observed. Furthermore, the pre-event water fraction will be overestimated 26.6% in typhoon storm and 15.3% in plum rain if the difference between rainfall and throughfall is ignored in a forest catchment. Finally, the three-component mixing model underpins the role of soil water in the discharge hydrograph in this humid forest watershed, which accounts for 10.9% and 28.3% of the total discharge in typhoon and plum rain respectively.”

4. In section 3.2 authors used two component mixing for hydrograph separation and the components are pre-event and event waters. Probably authors assumed groundwater, soil water, surface water etc. as one component and direct rainfall as another component. It is not clear what are the implications of separating pre-event and event rains.

Response: We are sorry for the misunderstanding. Usually in the traditional two-source isotopic hydrograph separation, one-member is event water (new water or rainfall) and the other member is pre-event water (old water, means stored water prior to the event, or groundwater). Actually, two-source mixing model is time-source separation model and three-component model is runoff generation sources model.

5. In section 3.2.2 it is not clear how contribution to pre-event rain from rainfall and throughfall are estimated (the scales for the % pre-event water by rain and throughfall are not given).  

Response: In two-source mixing model, if we use isotopic composition of rainfall as event water, we can calculate the contribution of event water and pre-event water. And if we use isotopic composition of throughfall as event water, we still can calculate the contribution of event water and pre-event water. Because of the difference of isotopic composition between rainfall and throughfall, the results of hydrograph separation is different using rainfall as event water and throughfall as event water.

The difference of isotopic composition between rainfall and throughfall is showed in figure 2.

6. In section 3.2.3 and Table 4 authors separately estimated the contributions of surface, soil and groundwater in what in the pre-event water or in the streamflow?

Response: In two-source mixing model, pre-event water refers to the water stored prior to the event, which includes groundwater and soil water and and ignores the contribution of soil water.

Table 4 separates the streamflow into surface water, soil water and groundwater.

7. Line 495-509: from the discussion in this paragraph, it seems authors estimated surface water, groundwater and soil water in the streamflow during the two rainfall events but it is not clear what is surface water here. Is it the combined water from pre-event, rainfall and throughfall?

Response: Surface water is mainly formed by rainfall (throughfall in forest basin). So in isotopic hydrograph separation, we usually use the isotopic composition of rainfall as that of event water in two-source mixing model and that of surface water in three-component model.

8. The conclusion section needs to be re-written removing unnecessary discussion.

Response: We have re-written the conclusion and removed unnecessary discussion.

As “By comparing hourly time resolution isotopic data, the differences in isotopic composition of rainfall throughfall, surface water, soil water, groundwater and river water in typical typhoon and plum rain events are studied. The results indicate that δ¹⁸O in precipitation and throughfall has significant temporal variation, and throughfall isotope is more enriched in heave isotopes than in open rainfall. Isotope values in precipitation in typhoon events had stronger variation compared with those in plum rain event. It is suggested that when separating a hydrograph, temporal variation in rainfall and the isotopic difference between rainfall and throughfall should be considered. Compared with rainfall, isotope concentrations in surface water varied smoothly. δD and δ¹⁸O averages in typhoons and plum rain events are approximately equal; however, isotopic variation in typhoon events is larger than that in plum rain events. In comparison, the groundwater δD and δ¹⁸O remained stable during two kinds of storm events. δD and δ¹⁸O of soil water had significant variations, and the variation in typhoons is more significant than that in plum rain.

 The comparison of hydrograph separation showed that the pre-event water component in rainfall episodes has a significant variation and in different rainfall types it has different features. Two-component isotopic hydrograph separation model results revealed that: 1) the variation range of pre-event water percentages in typhoon events was much bigger than that in plum rain; 2) pre-event fractions of plum rain were higher than in typhoon events; and 3) fractions in typhoon events had remarkable variation compared with gradual variation in plum rain. Furthermore, the pre-event water fraction was overestimated 26.6% in typhoon storm and 15.3% in plum rain if using rainfall isotopic value instead of throughfall isotopic value as event water isotopic value in this watershed, which means that in the forested watershed, the difference between rainfall and throughfall isotopic values should be considered in any rainfall type for hydrograph separation.

Following the early findings, in Hemuqiao, the three-component isotopic hydrograph separation model results showed that fractions of surface water and groundwater had inverse variation trends, and fractions of soil water varied with significant uncertainty which accounts for 10.9% and 28.3% of the total discharge in typhoon and plum rain respectively. The calculated three sources fractions in typhoon events changed significantly during the course of rainfall, and the fractions in plum rain varied much more in the earlier stage and tended to be steady.

In summary, the isotopic hydrograph separation in different rainfall types can help us for better understanding of runoff generation mechanisms and transit time, as well as flood forecasting during stream episodes. This paper mainly considered the influence of difference between rainfall and throughfall, temporal variation of rainfall isotopic value and soil water on isotopic hydrograph separation. Further studies can focus on the influence of temporal and spatial variation of water cycle elements on isotopic hydrograph separation. Furthermore, the coupling of isotope and hydrological models will improve our understanding of basin runoff generation and concentration and will provide advice for basin water resource planning and flood management.”

 Specific comments

9. Line 21: Please mention what isotopic compositions? Suggestion: Stable isotopic compositions (δ18O and δD) in different …..

Response: We have rewritten the whole abstract.

As “Using the stable isotopic composition difference of different water sources to separate the discharge hydrograph is helpful to better understand the runoff generation and concentration processes of the two typical rainfall events.”

10. Line 24: mention the name of the study area after ‘river water isotopic composition…’

Response: We have rewritten the whole abstract.

As “We selected a typical typhoon storm and plum rain occurred in 2016 in a small bamboo forest watershed in the lower reaches of the Yangtze River and investigated the temporal variation of rainfall, throughfall, surface water, soil water, groundwater and river water isotopic composition in these two rainfall events for the following purposes…”

11. Line 25: difference in variation in δ18O and δD in event-scale samples….

Response: We have corrected it.

As “(1) to quantify the difference in variation in and δ¹⁸O and δD in event-scale samples between different rainfall types,…”

12. Line 47: There has been some works on response of the hydrological cycle due to climate change and land-use/land-cover change….

Response: Thanks for the correction. We have corrected it.

As “There has been some works on response of the hydrological cycle due to climate change and land use/land cover change of the basin [3]”

13. Line 134: Figure 1 is not given anywhere in the manuscript.

Response: Sorry for the mistake. We have added Figure 1 in the manuscript.

Figure 1. Location of the Hemuqiao catchment and sampling sites.

14. Figure 3: No δ2H data presented in the figure as mentioned in the caption.

Response: Thanks for reminding. We have corrected the caption of figure 3.

As “Figure 3. Temporal variations of δ¹⁸O value in rainfall and throughfall. (a) Typhoon event; (b) plum rain event.”

15. Figure 4: Instead of naming individual symbols, authors could show them as a legend. Also best fit lines could be drawn for the individual datasets, e.g., a line for the soil water. The slope and intercepts would help to understand various secondary processes responsible for the deviation from LMWL and GMWL.

Response: We have redrawn figure 4 according to your suggestions as figure 3 in the revised manuscript.

Figure 3. All δ¹⁸O and δD data of rainfall, surface water, soil water, groundwater, and stream water relative to the local (LMWL) and global (GMWL) meteoric water lines. The LWML is calculated from rainfall collected in all rainfall events between 2015 and 2016 in the Hemuqiao catchment. (a) Typhoon event; (b) plum rain event.

16. Figure 5: Again use legends corresponding to different symbols. In Figure 5c and 5d, the scale for % event water is not shown.

Response: We have redrawn figure 5 according to your suggestions as figure 4 in the revised manuscript.

Figure 4. (a) Rainfall and surface water δ¹⁸O composition during the typhoon storm and rainfall amount. (b) δ¹⁸O values for soil water, groundwater and streamflow. (c) Discharge and results of the two-component mixing model, using δ¹⁸O for pre-event and event waters as a constant. (d) Discharge and results of the two-component mixing model, using temporal variation in δ18O in rainfall.

17. Line 312: … on of the sources of recharge to the river water

Response: Thanks for the improvement. We have corrected it.

As “Surface water is the composition of runoff collected from the gully after the rainfall falls to the ground and is one of sources of recharge to the river water.”

18. Line 324, 328: remove ‘depth’

Response: We have removed “depth” in Line 324 and 328.

As “In the 20160915 typhoon event, the total rainfall was 145.6 mm,…” and “…the total rainfall was 88.8 mm,…”

19. Line 388: please elaborate what do you mean by intense dynamic fractionation

Response: The slope of river water points is less than LWML, indicating that it has undergone intense dynamic fractionation. We have corrected it.

As “It can be seen that the points of river water are distributed around the LMWL, which means precipitation is the primary recharge source to river water; however, the slope is less than LMWL, indicating that is has undergone intense dynamic fractionation.”

20. Line 549-561: these are not conclusions, please remove. Also remove unnecessary discussion from the conclusion section and if required include them in discussion.

Response: Thanks for the suggestion. We have removed Line 549-561. We have corrected the caption “3 Results” into “3 Results and discussion” and removed some contents in the conclusions into “3 Results and discussion”. We have rewritten the conclusion part.

Reviewer 2 Report

Dear Authors,

Your paper deals with very interesting subject but there are too many common mistakes and some specific one that cannot be ignored. Let’s start from the easiest one: through whole text you are writing ∂D but you should as you did in tables in figures used expression ∂²H. in addition in the title change deuterium into hydrogen-2. Figure 1 is missing. On figures 4, 5, 6, 9 and 10 missing legend. You should for each type of water give the same symbol as you did but the clarification must be in the legend not on the graph. When it is on the graph it is difficult to read, so please changed it.  This is bamboo forest, you are only stating about evaporation rate, what is evapotranspiration rate? For me is very questionable the way that you abstracted the soil water. I thought that you used section cubs and vacuum pump but you made vacuum distillation, which from my opinion effect the results and lead to wrong conclusion. All your soil water samples are very below meteoric lines and groundwater is on meteoric lines indicating influence of evaporation process which I thing is caused by the way of extraction of water. As it generally known water from soil percolate into the deeper part of ground and become the groundwater. How you can explain that they are so isotopically distinct?

The other things that I can not understand what do you mean about expression surface water on page 11 and stream water on page 13? Then further, in the text the stream water is lost. Since Fig 1 is missing, I do not know do you by surface water mean on Yangtze river or some confluent of the river?

Taking into account points that are questionable, please rewrite discussion and conclusion part and I think you should not take into account the soil water.

In addition, I am not English native speaker, but some parts of the paper was very difficult to read and I am not sure that I understand clear the meaning of the text you wrote. Therefore, please can you after polishing of your text give someone to correct.

Author Response

1. Your paper deals with very interesting subject but there are too many common mistakes and some specific one that cannot be ignored. Let’s start from the easiest one: through whole text you are writing ∂D but you should as you did in tables in figures used expression ∂2H. in addition in the title change deuterium into hydrogen-2.

Response: Sorry for the misunderstanding. We have changed all δ²H into δD in the manuscript.

Table 1. Ranges and characteristics of stable isotope values in the water reservoirs during different storm event at Hemuqiao catchment.

Figure 4. All δ¹⁸O and δD data of rainfall, surface water, soil water, groundwater, and stream water relative to the local (LMWL) and global (GMWL) meteoric water lines. The LWML is calculated from rainfall collected in all rainfall events between 2015 and 2016 in the Hemuqiao catchment. (a) Typhoon event; (b) plum rain event.

2. Figure 1 is missing.

Response: Sorry for the mistake and we have added the figure 1 in the manuscript.

Figure 1. Location of the Hemuqiao catchment and sampling sites.

3. On figures 4, 5, 6, 9 and 10 missing legend. You should for each type of water give the same symbol as you did but the clarification must be in the legend not on the graph. When it is on the graph it is difficult to read, so please changed it.  

Response: We have redrawn figure 4-10 according to your suggestions and added the legend.

4. This is bamboo forest, you are only stating about evaporation rate, what is evapotranspiration rate?

Response: We did not measure the watershed evapotranspiration rate. We converted the water surface evaporation into basin evapotranspiration by multiplying a coefficient.

5. For me is very questionable the way that you abstracted the soil water. I thought that you used section cubs and vacuum pump but you made vacuum distillation, which from my opinion effect the results and lead to wrong conclusion. All your soil water samples are very below meteoric lines and groundwater is on meteoric lines indicating influence of evaporation process which I thing is caused by the way of extraction of water. As it generally known water from soil percolate into the deeper part of ground and become the groundwater. How you can explain that they are so isotopically distinct?

Response: Yes, different extraction method will influence the soil water isotopic value. Many scholars have done many studies, which showed that the soil water extracted by different soil water extraction method will be different, so it leads to the difference of isotopic value. Vacuum distillation is considered to be able to extract most of the soil water, so this method is used in this paper. In the future, we can study the effects of different extraction methods on soil water isotopic value in this watershed.

6. The other things that I can not understand what do you mean about expression surface water on page 11 and stream water on page 13? Then further, in the text the stream water is lost. Since Fig 1 is missing, I do not know do you by surface water mean on Yangtze river or some confluent of the river?

Response: Sorry for the missing of Figure 1 and we added it in the manuscript. Stream water includes surface water, soil water and groundwater. Usually, surface water is formed by rainfall. We dug a gully to collect surface water.

7. Taking into account points that are questionable, please rewrite discussion and conclusion part and I think you should not take into account the soil water.

Response: Thanks for the suggestion. We have rewritten the abstract and conclusion. We changed the “Results” into “Results and discussion” and removed some parts in conclusion into “Results and discussion”. With the development of hillslope hydrology, the role of soil water is gradually recognized by hydrologists in the humid basin in China. Hemuqiao watershed belongs to humid area and soil water cannot be ignored.

8. In addition, I am not English native speaker, but some parts of the paper was very difficult to read and I am not sure that I understand clear the meaning of the text you wrote. Therefore, please can you after polishing of your text give someone to correct.

Response: Thanks for the suggestion. We have rewritten some parts of the paper and asked PhD in USA to help us for English writing and editing.

Reviewer 3 Report

The manuscript contains valuable data, but there are problems that should be resolved before publication.

The main problem is the lack of readability of the work (some parts are really hard to read and understand). This is the part that the authors need to work hard on to make the manuscript not only interesting and readable, but ultimately citable.

In my opinion, the manuscript is too long and should be shortened; from the abstract to the conclusion (especially Abstract and Conclusion).

The tables are not clear at all, this is something the authors need to work on. 
As they are now, it is not at all clear to the reader what they are supposed to represent. The only table that is properly presented and organized is Table 4.

Figure 2 is unnecessary.

Fonts should be consistent (e.g., in Section 3.1.4).

The conclusion should be reworded to include only concluding remarks.

Author Response

1. The main problem is the lack of readability of the work (some parts are really hard to read and understand). This is the part that the authors need to work hard on to make the manuscript not only interesting and readable, but ultimately citable.

Response: Thanks for the suggestion. We have rewritten some parts of the paper and asked PhD in USA to help us for English writing and editing.

2. In my opinion, the manuscript is too long and should be shortened; from the abstract to the conclusion (especially Abstract and Conclusion).

Response: Thanks for the suggestion. We have rewritten the abstract and conclusion. We changed the “Results” into “Results and discussion” and removed some parts in conclusion into “Results and discussion”. Also, we have deleted some unnecessary discussion in the conclusion part.

3. The tables are not clear at all, this is something the authors need to work on. 
   As they are now, it is not at all clear to the reader what they are supposed to represent. The only table that is properly presented and organized is Table 4.

Response: Tables 1 and 2 showed the variation and statistical characteristics of isotopic value and EC between different water cycle elements, which used for hydrograph separation. Tables 3 and 4 showed the results of two-component and three-component models.

4. Figure 2 is unnecessary.

Response: We have deleted figure 2.

5. Fonts should be consistent (e.g., in Section 3.1.4).

Response: Thanks for the reminding. We have corrected it.

6. The conclusion should be reworded to include only concluding remarks.

Response: Thanks for the suggestion. We have rewritten the conclusion. We changed the “Results” into “Results and discussion” and removed some parts in conclusion into “Results and discussion”. Also, we have deleted some unnecessary discussion in the conclusion part.

Round 2

Reviewer 2 Report

Dear Authors,

most of remarks are corrected but you did not correct ∂D into ∂²H, please correct it.  

Author Response

We replaced δ²H with δD in the full manuscript. In this way, the full text expression will be unified.

Reviewer 3 Report

The authors have partially accepted the suggestions.
I suggest the authors to shorten the Abstract and Conclusion a bit more.
There is no space in the Abstract for goals and purposes. That is unnecessary and belongs in the Introduction.
Also, the 42 references in the Introduction are way too many. Reduce the number of references.
The tables still need to be reworked, the text wrapping looks bad (adjust column width and table size differently).
You should check the language and again all typos.

Author Response

Q1: I suggest the authors to shorten the Abstract and Conclusion a bit more.
There is no space in the Abstract for goals and purposes. That is unnecessary and belongs in the Introduction.

Response: Thanks for the suggestions. We have shortened the abstract and conclusion and deleted irrelevant parts.

Abstract: Typhoon storm and plum rain are two typical rainfall types in the middle and lower regions of the Yangtze River Basin, which frequently cause flood disasters in China. We intensively monitored a typical event for each of the typhoon storm and plum rain in 2016 in a small bamboo forest watershed within the lower region of the Yangtze River Basin, including isotopic compositions of rainfall, throughfall, surface water, soil water, groundwater and river water during the two rainfall events.  In order to better understand the runoff generation and concentration processes in response to the two-type rainfall events, we compared and analysed impacts of temporal variations of isotopic signals in rainfall, throughfall and soil water on isotopic hydrograph separation. Results showed that the variation range of rainfall δ¹⁸O was 3.7‰ in the typhoon and 5.2‰ in the plum rain, which were larger than that of throughfall, surface water, groundwater and river water. Although the variation of soil water isotopes was relatively high, large uncertainty might be embedded due to the influence of different soil water extraction methods. Considering temporal variations of rainfall isotopes during the event, a three-phase pattern of event water proportion during the rising limb of hydrograph can be obviously observed. This strongly evidences the importance of monitoring isotope temporal variations during rainfall events and its values in informing hydrological processes through hydrograph separation. Furthermore, the pre-event water fraction will be overestimated by 26.6% in typhoon storm and by 15.3% in plum rain, if the isotopic differences between rainfall and throughfall are ignored. Finally, the three-component mixing model underpins the role of soil water in the discharge hydrograph in this humid forest watershed, which accounts for 10.9% and 28.3% of the total discharge in typhoon and plum rain, respectively.

4 Conclusions

The hourly time resolution isotopic data of different compartments of catchment hydrological cycling during two typical rainfall events indicated that δ¹⁸O in precipitation and throughfall exhibited significant temporal variation, and throughfall isotope was more enriched in heavy isotopes than in open rainfall. Isotope values in precipitation in typhoon events had stronger variation compared with those in plum rain event. Compared with rainfall, isotope concentrations in surface water varied smoothly. δD and δ¹⁸O averages in typhoons and plum rain events were similar; however, isotopic variation in typhoon events was larger than that in plum rain events. In comparison, the groundwater δD and δ¹⁸O remained stable during the two-type storm events. δD and δ¹⁸O of soil water had significant variations, and the variation in typhoons was more significant than that in plum rain.

 The two-component isotopic hydrograph separation model results revealed that: 1) pre-event fractions of plum rain were higher than that of typhoon events; and 2) fractions in typhoon events exhibited remarkable variation compared with the moderate variation in plum rain. Furthermore, the pre-event water fraction was overestimated by 26.6% in typhoon storm and by 15.3% in plum rain when using rainfall isotopic value compared to that using throughfall isotopic value as event water isotopic value in this watershed. This means that, in the forested watershed, the difference between rainfall and throughfall isotopic values should be considered in both rainfall types for hydrograph separation.

 The three-component isotopic hydrograph separation model results in Hemuqiao showed that fractions of surface water and groundwater had inverse dynamic patterns, and fractions of soil water varied dynamically, accounting for 10.9% and 28.3% of the total discharge in typhoon and plum rain, respectively. The calculated three sources fractions in typhoon events changed significantly during the course of rainfall, and the fractions in plum rain varied much strongly in the earlier stage of the event and tended to be steady in the following stage.  

This paper mainly considered the differences between rainfall and throughfall and the impacts of considering temporal variation of rainfall and soil water isotopic values on isotopic hydrograph separation. Based on our study, further studies focusing on the influence of both temporal and spatial variations of different water sources on isotopic hydrograph separation are of highly interest. Furthermore, the coupling of isotope and hydrological models will improve our understanding of basin runoff generation and concentration and will provide advice for basin water resource planning and flood management.

Q2: Also, the 42 references in the Introduction are way too many. Reduce the number of references.

Response: Thanks for the suggestion. We deleted 20 references that were not relevant and were little relevant.

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Q3: The tables still need to be reworked, the text wrapping looks bad (adjust column width and table size differently).

Response: Thanks for the good suggestions. We have reworked the tables.

Table 1. Variation range and characteristics of stable isotope values in the water reservoirs during different storm event at Hemuqiao catchment

Table 2. Variation range and characteristics of EC in the water reservoirs during different storm event at Hemuqiao catchment

Table 3. Fractions of pre-event water in flood peak and averaged value for two rainfall events

Table 4. Characteristic fractions of surface water, soil water and groundwater for two rainfall events

Q4: You should check the language and again all typos.

Response: Thanks for the suggestion. We have invited postdoctoral studying abroad and foreign students with English official language in Hohai University to help us modify the language and typos in the manuscript.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.