Increased Mass Loss of Glaciers in the Sawir Mountains of Central Asia between 1959 and 2021

Round 1

Reviewer 1 Report

 

The study uses multi-source DEM data to determine the mass balance changes of Sawir Mountain glacier for about 62 years and validates the feasibility of the remote sensing detection method in the study area with in-situ measurement data. The amount of work performed in this study is extraordinary and the results are very exciting. The methodology used by the authors for elevation derivation, calculating mass balance, and estimating error is sound. The majority of my comments in the manuscript are to do with seeking a bit more clarification in the text. 

 

The paper is very well written with very good use of English language. Except some minor grammatical mistakes and word errors, this paper is written with a very good scientific style. The authors should check again the paper to correct these minor mistakes. In the Introduction, the authors have made an effort to provide the significance of studying glacier changes in the field, set the scientific questions well, and described the shortcomings of regional studies. At the end of the "Introduction", the authors pointed out the objectives of the study, but it was not clear to me what the aim exactly. Please think about what exactly you are trying to achieve in this paper, and spell it out clearly at the outset, maybe in another section after the introduction. You may organize the rest of the paper around that, remove the pieces of analysis that are not relevant to that theme altogether or at least move to the theme or supplementary.

 

In the Data and Method section, the article topic is based on geodetic method for mass balance calculation in the Sawir Mountains, and the Muz Taw glacier as the only monitored glacier in the Sawir Mountains can be used for the verification of the mass balance obtained by geodetic method. Therefore, the structure needs to be adjusted to swap 3.1 with 3.2. Correspondingly in the conclusion section it is suggested to swap the corresponding contents. In the results section there are so many figures. I suggest to mention the important figures (refer to other tables?) and provide their explanations. The discussion section gives the reasons for the increase in the number of glaciers. This should be mentioned first in the results section and this should be discussed in the discussion.

Specific comments

 

Line17 The Keyword of the manuscript is confusing. The article obviously uses actual in situ data to verify the feasibility of remote sensing means and to analyze the results of studies using remote sensing means, and there is no doubt that remote sensing or geodesy should be a keyword.

 

Line33 An obvious mistake, there should be spaces in the “which” and “can”.

 

Line35 In the author's article, "remote sensing data" appears several times. Based on the meaning of the author's article, it is suggested to change it to "geodetic method", which is more suitable for the article.

 

Line36-40 The presentation of the paper needs significant improvement.

 

Line39 “Further, the reliability of multi-source remote sensing data is assessed, which are utilized for exploring the variations of glacier surface altitude for the Sawir Mountain from 1959 to 2021.” This is a non-restrictive attributive clause, and it is wrong to use “are”.

 

Line45 Suggest change “area” to “glacier area”

 

Line46 “the altitude of the snow lines is between 3310 and 3410 m” The sentence introduces the snow line in the study area, not the author's research results, and should be cited in the reference.

 

Line47 Suggest change “ablate” to “ablation”

 

Line50 Is the Muz Taw glacier part of the Saur Mountain glacier? If so, the paragraph should need to explain the relationship of the Muz Taw glacier to the Sawir Mountains, such as being the only continuously monitored glacier in the Saur Mountains

 

Line51 “Sawir Mountains's northern slope”, General articles do not use this expression, it is suggest to change it “northern slope of Sawir Mountains”

 

Line57. “air temperature”, and everywhere else in the manuscript: please replace “air temperature” with “temperature”

 

Line59-60 “The average monthly precipitation is highest (55.06 mm) in July and lowest (16.61 mm) in December, with an average annual precipitation of 402.30 mm.” Precipitation data has been accurate to mm, there are two more decimal places after the decimal point, can be so accurate? If the weather data is measured by yourself, you should state the weather station model, accuracy, etc.

 

Line69 12–18 “splines/km2”, where 2 should be the superscript

 

Line79 Suggest change “thickness” to “the height of the stakes”

 

Line110 Suggest change “altitude” to “elevation”

 

Line151 Suggest change “BN” to “B_N”

 

Line154 Similar to "dimesions", "separately" is a word spelling error, suggest the author to check and revise.

 

Line170 Acor = πL2, where 2 should indicate the square of the area, suggest to check and modify。

 

Line243 Suggest removed “a”

 

Line244 “These glaciers were thinner during a 1959–2021 period. With the annual average altitude variation of −0.56 ±0.14 m·a⁻¹, the surface altitude change for the glaciers was −34.89 ±0.87 m.” The author should have wanted to express the change in elevation of the glacier，Suggest change “altitude variation” to “surface elevation change”, “altitude change” to “elevation change”

 

Line245 Suggest change “melting state” to “significantly mass loss”

 

Line246 “When the average mass balance was −0.47 ±0.11 m w. e. ·a⁻¹, the cumulative mass balance between 1959–2021 was −29.65 ±0.74 m w. e for the glaciers.” The meaning of this sentence is because the average mass balance was −0.47 ±0.11 m w. e. ·a⁻¹，threrfor the cumulative mass balance between 1959–2021 was −29.65 ±0.74 m w. e for the glaciers. Is there a causal relationship before and after?

 

Line292 Suggest change “simulated mass balance” to “geodetic mass balance”

 

Line345 “1788 ±1754 ng g–1”，-1 should be the superscript

 

Line381 Suggest reorganizing the reference according to the journal format

 

Figure and table

 

Line62-30 There is no scale and no glacier legend in Figure 1a; the bottom image in Figure 1b should indicate the source of the image

 

Line350 Suggest combining the four figures together

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Review of “Increased of the mass loss of glaciers in the Sawir Mountains of Central Asia between 1959 and 2021”.

Dear authors, this is a solid and important study dealing with previously unstudied region and using multisource DEMs and direct glaciological measurements for long period to evaluate MB. This work is definitely worth of publication but prior to that some issues should be improved, see major and minor comments below and minor comments in .pdf file.

Title: please correct English. Not “increased of the mass loss” but, for example, “increased mass loss”.

Abstract: please check English. Rewrite the first sentence, I don’t think that it is true that only a few glaciers have been studied as many mass balance measurements exist globally. Please mention the method of the DEM obtaining and clarify if the geodetic balance was calculated for all Sawir Mountains or only one or few glaciers. See also minor issues in pdf file. Give more keywords and rewrite the last one.

Introduction: short and general. I would like to see a little bit extended introduction. You have stated that previous studies are scares and that the region is important due to glaciers as a water reserve. It is true but it is true for almost all glaciers. Are there any other important issues, studies that have been performed, data availability for the generation of DEM? I suggest trying to define reasons why anybody should read this paper, what is novelty except of location and new in-situ measurements? Other minor comments in pdf file.

Study site: many minor issues, please check .pdf file. In the last sentence, please check the numbers of precipitation, there is an error in highest or average precipitation.

Figure 1: it could be improved. For example, the grid of coordinates is inside the map in the a image and outside in b, better put coordinates outside in both. There is no scale in the a image. It is also not clear why you have written the names of some glaciers, leave them if they are mentioned in the text but otherwise, you could give names of mountain ranges instead. I do not like the colour of the DEM in the background personally, it does not show clearly the differences of elevation. Please mention the source and date of the satellite image in the background of b image.

Data and Method:

3.2.1 Digital Elevation Models (DEMs): can you evaluate specifically the accuracy of these DEMs as well and describe how these errors are affected after the co-registration.

Please explain, why do you choose such a density of ice – 850 kg/m3. Based on literature or in-situ direct measurements. Why did you not try to consider the density variations of snow and firn in the accumulation zone?

Results: it may be beneficial to add the map with contours or/and colours of interpolated glaciological mass balance of the studied glacier for the measurement period.

Lines 248-249 – rewrite the sentence, there maybe error in mentioned period as it includes all your study period and glaciers cannot be thinner in all study period compared to all study period.

In all text please check the usage of superscript, it is missing in many places, in specially when you use “a-1” as in line 249 for example.

Line 250: I am not sure you can state that “For 62 years, these glaciers have been in the melting state”. It is true for the study period but you don’t have information for individual years, maybe there were years with positive mass balance.

What I miss in the Results or Discussion is the comparison of glacier surface elevation and mass balance change between individual glaciers. I do not mean that you have to describe changes of each glacier, but are there any differences in change rate depending on glacier morphologies and geometry (area, length, height, slope, aspect)? Do larger or smaller glaciers change more rapidly, or glaciers, which tongues are located at lower elevations in your studied mountain range? This kind of analysis is missing.

 

Discussion:

Line 283 – the geodetic mass balance is not record, it can be calculated for many glaciers, please rewrite the first part of the first sentence. You can write that your study is the first where the GMB is evaluated for such a long period for Central Asia region.

Figure 6. Please clarify what we see in left image – glaciological or geodetic changes. Also what is shown in image on the right – I understand that measured MB is glaciological but what is simulated MB? How did you simulate it, it is not described. Do you mean geodetic MB?

5.2 Comparison with neighboring mountain glaciers: the reference style in this paragraph is wrong.

You mention that glaciers in Sawir mountains losses their mass twice as much as other glaciers in neighbouring mountain ridges, and you give only one reason for it – that your studied glaciers are smaller. Are there any more reasons? Is this effect only due to size or there are more specific factors like the size of accumulation area, glacier slope aspect, climatic variables? You could slightly extend this discussion as this issue is very important. Does it mean that these glaciers are more sensitive to climate change?

5.3. Climate background. You mention the annual mean air temperature of –5.7 °C from 2010 to 2021 and then 4.17 °C for 1961 to 2021. From these data it seems that it has become considerably colder but as I understand for the first value you used the data from the meteorological station near the glacier. Please describe it here, also give some information again that the two meteorological stations which data you have analysed in details are located away from the glacier where the temperature seems to be considerably warmer. Based on that, the analyses show the warming of region but do not very well represent the possible temperature changes exactly at the glaciers. This should be noted in text.

 

Line 328. What do you mean by retreating thinning?

Line 348-349. Did you measure the BC and mineral dust concentration on the glacier surface? It was not mentioned in methods. Or is it from literature, reference is needed then. And what is average concentrations, in how many places did you measure this? No methodology is described.

Lines 350-353. What do you mean by moraine? End moraine, medial moraine? Or supraglacial debris/till? I also does not agree with your assumption that large supraglacial debris increase glacier melting. It is contrary, several studies have shown that areas of glaciers which are debris-covered, melt slower due to the insulating effect.

I think that as you have described very shortly the BC and mineral dust potential impact without methodological description and as your conclusion about moraines seems to be wrong, (moraines, large supraglacial debris and small mineral particles have very different impact on glacier surface ablation) I suggest to delete the subchapter 5.4. together with Figure 8.

 

Conclusions: are not bad overall but they are based on many numbers, it is more like description of results in short. I suggest deleting some numbers as noted in .pdf file and you should add some conclusions which could make your study more interesting for broader audience. What your study concludes on overall glacier and climate change in the region? How it differs from other regions and why? Incorporate something from chapter 5.2. Give some conclusion related to the usage of multisource DEMs for evaluation of GMB. What do you suggest fur future studies, what kind of other methods should be used in future studies in this region?

 

 

Comments for author File: Comments.pdf

Author Response

Please see the attachment

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

I thank the authors for the changes they have made to the manuscript. I found only minor issues that should be further addressed. All comments and corrections are available in pdf. file. The most important are listed here:

1. Abstract. Some English suggestions in pdf. file. Please rewrite these keywords as shrinkage and climate background are too wide keywords and not understandable without context.

2. Introduction. Line 60. Are these really the first field observations? Previously you mentioned other studies where field data were acquired like GPR. Also clarify what is material balance.

3. Study site. Line 72. How fast? it is very relative, please specify the speed of glaciers and how it was evaluated in the mentioned study.

line 77. As I understand the ice thickness you refer to is from GPR data, please check are there any information related to glacier thermal structure - is it a temperate, cold or polythermal glacier? And what about the thermal structure od other glaciers in the region? Is is studied at all? It has very important implications on glacier dynamics.

4. Methods. Lines 202-203. I still would like to see the average densities you used for snow, and firn as it is not clear if you used 850 in general or several different densities for snow and firn, please clarify.

5. Discussion. Lines 351-352. Please rewrite the sentence as it is not clear what are you saying there.

Line 354. Please explain why the area of small glaciers increased in the beginning of your study period. Was it related to air temperatures or other factors?

Line 355. What do you mean by - on all slopes? please clarify. Also, to which period are you referring to here? Please check the English in this newly added paragraph of Glacier morphology and geometry.

Line 360. Change to "elevation of glacier terminus".

6. Conslussions. Some small issues need to be clarified, check the pdf. file.

Lines 401-402. Please rewrite this sentence stating that this study presents the first data on glaciological and long-time series of geodetic mass balance estimates.

Line 418. please give here the rates of warming per decade.

Line 421. you could also add information on the slope as I remember the majority of these small glaciers, which are retreating rapidly were facing south.

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.docx