Impacts of Climate Change on Permafrost and Hydrological Processes in Northeast China

Round 1

Reviewer 1 Report

Using field borehole data to simulate the permafrost fugacity in the permafrost regions of Northeast China during 2000-2020, combined with the analysis of climate and other hydrological environments of several major river basins in Northeast China, a distributed hydrological model was developed for several river basins during the study period respectively, and the influence of permafrost on runoff in Northeast China was analyzed.

Due to the presence of permafrost, the permafrost regions form a special runoff yield and concentration process and change the water circulation process by affecting regional evapotranspiration and groundwater, so that the basin runoff shows certain intra-annual variation. In the context of global warming, there is a tendency of increasing annual runoff in the permafrost regions of Northeast China. The presence of permafrost will reduce the soil infiltration rate, and the snow and ice melt water in spring in regions with more stable permafrost, greater permafrost thickness and thinner active layer thickness will have less groundwater replenishment.

The paper content very wide valuable data. It should be published after minor revision as below.

 

General Remarks

Abstract - Please do not use abbreviation in abstract or provide the full name.

Conclusions are too long and could be shortened by 30%

 Detailed remarks

 1.        Point 2.3.1. Some references should be added.

2.        Point 2.3.4 Some references connected with SWAT method should be added.

3.        Figure 1 should be self-explaining. Please add proper information.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

This manuscript demonstrated the results that climate changes performed on the permafrost and hydrological processes in Northeast region in China. The authors used the improved ground freezing number model as the simulated method to obtain the spatial distribution of permafrost. The results showed the degradation of permafrost area in Northeast China during the past 20 years, and the changes of the ice storage volume and water released. The data were useful and could provide information of the environmental protection of permafrost in China. I suggested that this paper could be considered for acceptance after some revisions.

 

Specific comments:

1. The introduction should be more concise.

2. The conclusion part was too long, please revise it to make the conclusions more clearly.

3. Please check and unify the format of references in accordance with the guidelines of “Toxics”.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments on Sustainability-2246975

• Grammar, punctuation, capitalisation and hyphenation across lines need to be corrected throughout.

• The editors should decide if the URL and access dates for the data sources (lines 283-317) should be moved to the references or remain in the main text.

• Presumably the manuscript formatting will be done by the journal to remove inconsistent line spacings and other formatting errors, such as ‘m3’ for ‘m3’.

• The paper contains novel material.

• The presentation of data needs to be more detailed and clearer.

• I suggest that the authors should present the observed changes in permafrost distribution between 2000 and 2020 before presenting the extrapolated model for 2100.

Author Response

Dear professor:

On behalf of all the authors, we appreciate you very much for your positive and constructive comments on our manuscript entitled “Impacts of climate change on permafrost and hydrological processes in Northeast China” (ID: sustainability-2246975).

We have carefully studied your suggestions and have tried our best to improve and revise the manuscript according to the comments. The followings are the responses and revisions I have made in response to the suggestions on an item-by-item basis. Thanks again for your hard work.

General Remarks

1. Grammar, punctuation, capitalization, and hyphenation across lines need to be corrected

throughout.

Response: Thank you for your reminder. We are sorry for these low-level mistakes we made, and after receiving your reminder we have checked the article and corrected the relevant content.

2. The editors should decide if the URL and access dates for the data sources (lines 283-317)

should be moved to the references or remain in the main text.

Response: Thanks to your thoughtful consideration, we referenced other articles that have been published in the journal Sustainability. Since many published articles in sustainability journals keep the URLs and access dates of the data sources in the text, we decided after discussion to keep these in the main text for easy reference and access by interested readers.

3. Presumably the manuscript formatting will be done by the journal to remove inconsistent

line spacings and other formatting errors, such as ‘m3’ for ‘m3 ’.

Response: Thank you for your reminder. We are very sorry for these formatting errors caused by our oversight, we have checked the article and corrected the relevant content.

4. The paper contains novel material.

Response: Thank you for your recognition, and we will continue to make progress in our future research with your encouragement.

5. The presentation of data needs to be more detailed and clearer.

Response: Thank you for your suggestion. After receiving your suggestion, we have added the contents and data to the article according to your suggestions and questions in the article, to make the expression of the article more detailed and clear.

6. I suggest that the authors should present the observed changes in permafrost distribution

between 2000 and 2020 before presenting the extrapolated model for 2100.

Response: Thanks for your suggestion, our study in this paper focuses on the release of large amounts of water from the ice melt in the soil during permafrost degradation, the impact of this process on the hydrological environment, and the summary of the relevant laws in this process. Concerning the changes in the distribution of permafrost and the changes in the active layer, We think that the status and distribution change of ice storage in the current scenario obtained by the calculation method based on this change proposed by us will be presented as a result, which is more in line with the content of the journal topic 'Climate Change and Freshwater Sustainability' submitted by this paper. More details on the distribution and changes of permafrost and active layer from 2000 to 2020 are presented in our article in the Sustainability journal in July 2022. (Article name: Spatial Distribution and Variation Characteristics of Permafrost Temperature in Northeast China, DOI: 10.3390/su14138178), which is also reflected in the references of this paper.

Specific comments

(We have also replied to each of these comments in the corresponding place in the uploaded attachment, and you can also check each of them in the corresponding place in the attachment.)

Comment No.1: This chapter needs to be more structured and more focused on the work presented in this paper. It currently reads like a collage of statements taken from various papers.

Response: Thank you very much for your suggestion, We have found this problem and made improvements in the second revision submitted on February 25. We received your review report on the first version on the 28th after submission. Your detailed and professional suggestions made us take them very seriously, so we have carefully reworked the whole text according to your suggestions one by one, and a third version of the article was generated in response to your suggestions, and the revised article was uploaded again through the platform. We do our best to make the article better and more rigorous based on your suggestions. Thank you again for your hard work and valuable comments, We are very grateful.

Comment No.2: Poor phrasing. Permafrost is defined by temperature alone (frozen for at least 2 consecutive years), it can occur in both soil and rock, so it is not a rock formation.

Response: We are very sorry for the inaccuracy of our wording and translation, and we thank you for your professional reminder that this sentence has been changed to ‘Permafrost is a product of the comprehensive action of the atmosphere and the lithosphere, which is frozen and extremely sensitive to temperature changes’.

Comment No.3: Better: 'water bound as ice'.

Response: Thank you for your suggestion. Taking into account your overall suggestion for the introduction, we have adjusted the introduction as a whole to make it more structured and concise, so this sentence has been removed, but we have kept your suggestion here in mind and will pay more attention to it in future articles.

Comment No.4: What do you mean? Please clarify.

Response: Thank you for your reminder that we have misrepresented here, and in the second version of the submitted manuscript, this sentence was changed to ‘The permafrost layer is usually considered as an aquiclude.’ Meaning that the permafrost layer is usually considered to be difficult for water to pass through and acts as a kind of water-resisting layer

Comment No.5: This sentence needs rephrasing and clarifying.

Response: Thank you very much, after your reminder, we also feel that the expression here is unclear and redundant, and needs to be improved. So we have combined the sentence you pointed out with the next sentence and changed it to ‘The mean annual ground temperature method refers to the use of the value of ground temperature that remains constant over a long time, almost unaffected by surface temperature fluctuations due to a certain depth, as a method of determining the presence or absence of permafrost.’

Comment No.6: If you wish to include the names of these river systems then you also should include a map showing the names.

Response: Thank you for your suggestion. We have shown the detailed location of each watershed distribution in Figure 2, and after receiving your suggestion, we have adjusted what you pointed out and added additional descriptions. The original text was adjusted to ‘The distribution of major river basins in the Northeast permafrost region is shown in Figure 2. The hydrological area in the northern part of the Greater Khingan Mountains mainly includes the Jiliu River Basin, the Eimur River Basin, the Pangu River Basin, and the Huma River Basin, which are radially shaped and injected into the Heilongjiang River respectively.’

Comment No.7: You introduce three regions with distinctive climatic differences here. Again, you should present a map showing these regions as not all readers will be familiar with are region.

Response: Thanks to your suggestion, we have also shown the location of these river basins in Figure 2 and added additional descriptions here at your suggestion to make the content of the article clearer and more explicit.

Comment No.8: 1km for consistency with line 287.

Response: We apologize for the lack of discipline here, and we will pay more attention to this point when writing this article in the future. Thank you for pointing out. This has been changed to '1km', which is consistent with the above article.

Comment No.9: Give the equivalent in km.

Response: Thank you for your suggestion. The unit of measurement for the resolution provided by the data source is °, and 0.1°*0.1° is the resolution expressed in latitude and longitude. The length of one degree apart in longitude varies with the latitude of the location, and it might be inaccurate to measure in km as a constant value due to the large latitude range covered by the study area in this paper. For this reason, we keep the resolution measurement units provided by the data source here, but we unify the resolution at each pixel at different latitudes in our calculations through the resampling function in ArcGIS, as explained in the second paragraph of Section 2.3.1.

Comment No.10: Where does the information 'stable, semi-stable and transitional type' permafrost in this figure come from?

Response: We state the source of the permafrost distribution and zoning information at the end of the second paragraph of the introduction. The permafrost distribution and zonation in this figure are from a citation of the results of our article published in July 2022 in the journal Sustainability, (article name: Spatial Distribution and Variation Characteristics of Permafrost Temperature in Northeast China, DOI: 10.3390/su14138178), which we have also reflected in the references.

Comment No.11: Include reference number

Response: Thank you for your reminder. In the revised second edition of the document, we added the serial number after each quoted discourse according to the citation format provided on the official website of the journal. The revised version has been uploaded to the platform again, and the citation number here is [28,29].

Comment No.12: Presumably these equations were developed by Nelson? Please add citation.

Response: Thank you for your reminder. In the revised second edition of the document, we added the serial number after each quoted discourse according to the citation format provided on the official website of the journal. The revised version has been uploaded to the platform again, and the citation number here is [29].

Comment No.13: Water content w is usually defined as (mass of water) / (mass of soil solids). rather than (mass of water) / (Soil volume).

Response: Thank you for your professional advice, we had considered this as well. Considering the current soil moisture content is broadly expressed as follows: 1. Soil water content is expressed as a percentage of weight, that is, expressed as a percentage of the weight of water contained in the soil to the weight of the dry soil. 2. Soil water content expressed as a percentage of volume, that is, expressed as a percentage of soil water volume to the volume of the unit soil, that is, soil water content = (wet soil Weight - dry soil weight)/dry soil × 100%; 3. Soil water content expressed in terms of water layer thickness, that is, the water content in a certain depth of the map layer is converted into the depth of the water layer expressed in mm; 4. Relative water content, the soil water content is converted into a percentage of the field water holding capacity or full storage capacity to express the relative content of soil water. But what we need to get in this paper is not the soil water content, but the unfrozen water content, the main purpose of Equation 5 in this paper is to obtain a calculation that can approach the value of unfrozen water content over a large area. The calculation and estimation of unfrozen water content, both at the micro and macro level has been a complex problem that has been studied and urgently needed to be solved by many people in the past years, such as the studies in the introduction [27-29], which also tried to obtain a method of relative value or distribution pattern of unfrozen water content in spatial distribution by linking the TVDI and soil water content patterns as if. Therefore, in this paper, after trying to use the methods of soil capacity conversion and field water holding capacity calculation obtained from the SPAW software mentioned in the paper, the results of the spatial distribution of remote sensing data calculated by Equation 5 in the paper can also approximate the spatial distribution of unfrozen water values. Therefore, in this paper, after trying to convert the soil capacity obtained from the SPAW software mentioned in the paper and calculate the field water holding capacity, the results of the spatial distribution of remote sensing data calculated in Equation 5 in the paper can also approximate the spatial distribution patterns of unfrozen water values. Thanks to your suggestions, we will also do more relevant research and consideration in future studies to improve the accuracy of the calculation of the distribution patterns of unfrozen water content on a large scale.

Comment No.14: Include a citation for Eq. 10 - 12. If the equations were developed by the authors then give more details on how these empirical relationships were found.

Response: Thank you for your reminder. In the revised second edition of the document, we added the serial number after each quoted discourse according to the citation format provided on the official website of the journal. The revised version has been uploaded to the platform again, and the citation number here is [56].

Comment No.15: How does Sw relate to the water content defined in Eq. 5?

Response: We apologize for the lack of clarity in the description here, and we have provided a more detailed description of the places you pointed out in the revised version 2 document. The revised article adds specific descriptions, sources, and usage of the models and formulas used in Equations 10-12. Sw is the amount of water available to the soil in the SCN model proposed by the United States Department of Agriculture Soil Conservation Service (USDASCS), and in the study of the article, there is no direct computational link to the unfrozen water content obtained in Equation 5 from the relevant calculations of the software SPAW used to improve the calculation of the permafrost distribution.

Comment No.16: You mean slow?

Response: We have focused here on indicating a longer span of time, and after you questioned it, in the context of the article below, it was changed to ‘Soil freezing/thawing in high latitudes is a long-term process, and the permafrost in the Great Khingan Mountains starts to freeze one after another in November of the calendar year, and thawing starts one after another in late March of the following year.’

Comment No.17: Again, a citation is needed for equations 14 and 15. If the equations were developed by the authors please include more details how they were derived.

Response: Thank you for your reminder, and we have added the citation [60] here in response to your reminder.

Comment No.18: This is not clear, please rephrase and clarify.

Response: Thank you for your suggestion, we have changed this to’ We expressed the ice content in the soil layer of each pixel by converting it into the thickness of the ice layer (m), and superimposed the ice content calculated for each pixel point in the study region within the set elevation range in units of 200 m in elevation, and superimposed the ice content calculated for all pixels in the study region within the set unit latitude range in units of ° in latitude. The spatial distribution of ice reserves in Northeast China under the current scenario, and the variation of ice reserves with latitude and elevation were obtained (Fig. 4).’, to make the presentation of the article clearer.

Comment No.19: In line 519 you state that you have data from 2000 until 2020. It would make sense to present here the change in the permafrost between 2000 and 2020 and then extrapolate until 2100.

As you mention the thickness of the active layer in this paper you also should show how this changed between 2000 and 2020 and show the extrapolation to 2100.

It would also be good to show some areas with a higher resolution, e.g. typical example areas for different environments.

Response: Thanks for your suggestion, our study in this paper focuses on the release of large amounts of water from the ice melt in the soil during permafrost degradation, the impact of this process on the hydrological environment, and the summary of the relevant laws in this process. Concerning the changes in the distribution of permafrost and the changes in the active layer, We think that the status and distribution change of ice storage in the current scenario obtained by the calculation method based on this change proposed by us will be presented as a result, which is more in line with the content of the journal topic 'Climate Change and Freshwater Sustainability' submitted by this paper. More details on the distribution and changes of permafrost and active layer from 2000 to 2020 are presented in our article in the Sustainability journal in July 2022. (Article name: Spatial Distribution and Variation Characteristics of Permafrost Temperature in Northeast China, DOI: 10.3390/su14138178), which is also reflected in the references of this paper. We appreciate and have adopted your suggestion to add the presentation of example regions with different environments in Figure 3 to make the presentation of the results more clear. The added section is also partially shown in the next comment reply.

Comment No.20: Please explain why there is maximum ice content at 1000m elevation and why the ice content at elevations >1200m is so low. Please also see the next comment.

Response: Thank you for your reminder. After your reminder, we have considered the inconvenience caused to readers in other regions by our inadequate presentation here, and we are very sorry for this, and we have added this to the article with the following content ‘Since most of the permafrost in northeast China is located in the Greater and Lesser Khinggan Mountains, and most of the regions in the Greater and Lesser Khinggan Mountains are between 800m and 1200m in elevation, and there even are not many peaks with an altitude of more than 1400 meters. but the Changbai Mountains in the southeast coastal area of northeast China are very high in elevation, and the highest peak elevation is the highest elevation in the entire northeast region, but it accounts for a very small proportion of the area of the whole Northeast China and is much smaller than the permafrost region of the Greater and Lesser Khinggan Mountains, which makes the ice storage in Northeast China reach a maximum at the elevation of 1000m, while the value of the elevation above 1200m is gradually decreasing. Figure 3(g) shows the elevation distribution in northeast China, and two watersheds with different latitudes and large elevation changes are selected as examples to illustrate the spatial distribution of the present ice reserves in the northeast China permafrost region and the predicted changes in 100 years. To better show the true latitudinal span of the shown watersheds on the Earth, the projection coordinates of Figure 3 are taken in the Krasovsky_1940_Albers projection mode that takes into account the curvature of the Earth. It can be seen that in the next 100 years, the ice reserves in Northeast China will be significantly reduced, and the lower latitudes will be degraded more rapidly than the higher latitudes, with almost no permafrost remaining in the southern edge of the present tundra and the subsurface ice disappearing. The comparison between the Jiliu River basin in Fig. 3(h) and the Hailar River basin in Fig. 3(i) shows that the lower elevation areas are degraded more rapidly than the higher elevation areas. The ice storage in the same latitudinal range tends to decrease from the ridges to the lower elevations. Many large rivers in Northeast China have thawed areas underneath them, where permafrost does not exist. Due to the special geological structure, there are volcanoes and underground hot springs in some places, and the river water temperature is relatively high, so the future permafrost degradation spreads along the river to both sides of the river, and the ice storage volume gradually decreases along the river to both sides of the river.’

Comment No.21: Here you are explaining the high water content in the active layer here, is that the same as the 'ice storage in permafrost' in Figure 3? Please clarify.

Response: We apologize for the confusion caused by our inappropriate expression here, which has been changed to‘permafrost layer under the "active layer" starts to melt downwards from the top.’ To make the messages expressed in the article more clear.

Comment No.22: The numbers in this columns don't match this column description. According to the description 3 numbers would be expected, but 4 are given. Are these ranges of values? Then the description in the footnote that these are average values can't be correct. The width and depth naturally vary over the length of the river, where are the reference points for width and depth? The footnote refers to an average over a region, what region is used?

Response: Thank you for your helpful reminder that our statement here in the article was inappropriate and inaccurate, and we have changed it to ‘The length/width/depth of the rivers shown in the table are the length/width range/average depth of the corresponding river main stem in the list. The runoff in the table is the runoff recorded at the control hydrological stations of the main streams of the rivers listed in the table, and the specific locations of the hydrological stations are shown in Figure 2. And the temperature, precipitation, evaporation, forest percentage coverage, and permafrost depth of each shown watershed are taken as the average value within the whole watershed corresponding from 2000 to 2020.’ In section 3.1 of the results, it is mentioned that many large rivers in Northeast China have thawed through zones underneath them and do not have permafrost. This is also reflected in the details shown in the added Figure 3, and in general, the large length, width, and depth of rivers tend to have higher river runoff, which can also have an impact on the results of watershed simulations, and since there are a large number of watersheds studied in this paper with a wide distribution, readers in other regions do not have a clear knowledge of the specifics of the rivers we mention and the environment in which they are located. For these reasons we also list here the width and depth of each river to help the reader better understand the specific river scale for each of the rivers studied in this paper.

Comment No.23: Is this the annual runoff of the river or the whole watershed?

Response: The runoff in the table is the runoff recorded at the control hydrological stations of the main streams of the rivers listed in the table, and the specific locations of the hydrological stations are shown in Figure 2. We apologize for our inadequate expression here, and after receiving your query, we have added this to the footnotes of the table to make the content of the article more rigorous.

Comment No.24: Presumably this should be 10^8 m^3?

Response: We apologize for the oversight in our formatting here, and after receiving your reminder we have checked the formatting here and have corrected it one by one.

Comment No.25: Length and width of the lake?

Response: Since the surface of Hulun Lake is irregularly oblique rectangular, we did not add the length and width of Hulun Lake because we thought it might be ambiguous in the presentation due to different observation angles while writing the article. After hearing your question, we also recognize that adding relevant information can make our article better, so we have added the area of Hulun Lake '2.339 *109 m3 in area' here as additional information.

Comment No.26: If it says max/min then a maximum and a minimum number would be expected.

Response: Thank you for your suggestion. After receiving your suggestion, we have added specific values for the maximum and minimum values here ‘max /min is 18.42/0.865=21.29’.

Comment No.27: 'Discussion' normally refers to a chapter where the author's own data are compared with literature data. This does not seem to be the case here, so I suggest to rename the chapter to 'Analysis'.

Response: Thank you for your suggestion. In the writing template given on the Sustainability website, the specific requirements set out in the Chapter 4 discussion are ‘ Authors should discuss the results and how they can be interpreted from the perspective of previous studies and of the working hypotheses. The findings and their implications should be discussed in the broadest context possible. Future research directions may also be highlighted.’ We feel that the arrangement of our content here is compatible with the requirements of the journal and we appreciate and will keep your suggestion in mind and will pay more attention to similar situations in future articles.

Comment No.28: It would be useful to also show the air temperatures in b-d.

Response: Thank you for your suggestion. We did not add the temperature curves in b-d because we considered that the temperature changes between the basins are not very obvious with the curves in Figure 4a since the basins are in close proximity to each other, and Figure a can already represents the trend of climate change in each basin. But after seeing your suggestion, we have added the distribution of the mean annual air temperature and the mean annual precipitation changes in each watershed in Figure 4 to supplement the relevant content.

Comment No.29: If 4a shows the average of all watersheds, presumably 4b-4d refer to specific watersheds in different environments? Some clarification is given in the text but the figure caption should be clear on its own.

Response: Thank you for your reminder. Figure 4 in the text shows the universal characteristics of all watersheds, and 4b-4d refers to the performance patterns of the watersheds in different environments, and the specific environments we have described individually in the title of Figure 4. ‘(b) Precipitation directly generates surface runoff. (c) Infiltration of precipitation into the "active layer" to form subsurface flow to recharge the river. (d) Upwelling of pressurized water to recharge rivers.’

Comment No.30: This sentence is misleading, please change.

Response: Thank you for your reminder, the place you pointed out in the article has been changed to ‘Most of the permafrost regions in Northeast China have the climate conditions of rain and heat synchronization.’

Comment No.31: Please include citations

Response: Thank you for your reminder, we have added the reference here with the literature number [61-62].

Comment No.32: Adding suitable graphs or figures would make the section from line 718 -790 much clearer.

Response: Thank you for your suggestion, we have adopted your suggestion and added relevant pictures in Figure 4, combined with the information listed in Table 1 in the text, we believe it can make the content of the article more clearly expressed.

Comment No.33: In this section you should refer back to the figures illustrating the your statements.

Response: Thanks to your suggestion, we have adjusted the content of the conclusion of the article, and the adjusted article has been uploaded to the website of the Journal of Sustainability. While adjusting the content of the conclusion of the paper, we have also refined the content of the conclusion to make the article more concise and clear. Once again, thank you from the bottom of my heart for your guidance.

We would like to express our great appreciation to you for your comments on our paper.

Thank you and best regards.

Yours sincerely,

Wei Shan and Yan Wang

Author Response File: Author Response.pdf