Dear authors,

Attached you find my feedback to your manuscript.

Review of Xie et al., article 2025_4573 entitledGlacier Mass Balance and Its Response to Heatwaves for Kangxiwa Glacier in the Eastern Pamir: Insights from Time-Lapse Photography and In-situ Measurements“ submitted to The Cryosphere.

The manuscript by Xie et al. addresses the use of time lapse photography to understand the inter-seasonal and inter-annual variability of glacier mass balance through high temporal resolution accumulation and ablation data on a glacier in the Eastern Pamir. The authors place particular attention on heatwave events during the extreme 2022 summer to understand their relative contributions to the overall mass loss and distinguish the accompanying climatic conditions during those different events. The authors present a valuable data series in an under-represented and hydro-climatically interesting and anomalous region. They demonstrate the value of detailed and high temporal resolution data to aid our understanding of the inter-seasonal and inter-annual differences of mass balance and their relationship to some climatic drivers, most notably to air temperature during regional heatwave events. 

The manuscript is reasonably well written and the figures are clear and generally informative, if not a bit redundant at times. The work is of sound scientific quality for the most part, but I struggle to find clearly-driven or stated research questions and support for a few statements in the manuscript. I believe that the relevance of the work needs to be more strongly supported in relation to the past research in the region. Moreover, a clearer presentation and discussion of the magnitude of summer heatwave events during the last decades is required, especially in the context of its role during the anomalous periods of stable or positive mass balance years. A sensitivity to an extreme heatwave year (2021-2022) alone is not suggestive of a termination of the Karakoram-Pamir anomaly as the authors state in their abstract. In several places, there are also unclear statements or those that are not clearly backed by robust tests (e.g. the relative role of precipitation and accumulation on the glacier compared to melt events). Ultimately, the relevance of the presented work needs to be placed better into the context of the broader mass balance patterns and changes over the last decades and considering the role of precipitation and snowfall/albedo. The authors should also work hard to improve the clarity of the text and spelling in several places. Based upon my comments below, I suggest major revisions before the manuscript could be accepted by the journal.

Major comments

1. Research Questions: The manuscript provides no clearly stated research questions that help to direct the main goal of the analysis and its context. The title indicates that heatwaves form the main focus of the paper and timelapse imagery is the tool by which it is evaluated, but the focus falls upon a single extreme year with no historical context regarding heatwave occurrence (or inference from reanalysis etc). While most of the material to frame this is available in the introduction, the goals (or even hypotheses) of the manuscript need to be clearly motivated and established at the end of the introduction.
2. Relevance and context within an anomalous region: The authors present some new understanding in a relatively under-studied region of anomalous glacier behaviour, but focus largely upon the role of temperature during summer heatwaves in one year toward affecting mass balance. Nevertheless, in such a region where winter and spring accumulation regimes dominate, the role of antecedent precipitation, accumulation and surface conditions will also have a strong impact on the annual mass balance. The variability of precipitation is one of the suggested mechanisms that was driving the mass balance anomaly for the region (e.g. Farinotti et al., 2020; de Kok et al., 2018) that has now likely ended (e.g. Hugonnet et al., 2021; Jouberton et al., 2025). However the authors present an unclear case for the role of precipitation variability in the winter and spring and, again, provide little broader context related to historical changes. Additional discussion and reframing of the manuscript are needed to provide a more valuable insight for the reader.
3. Uncertainties: The estimation of uncertainties and use of the additional mass balance stake observations (i.e. not at the timelapse camera locations - Figure 1) needs more clarification and justification in the study. The glacier-wide mass balance is computed from a weighted average of the three-point mass balance derived at the location of the timelapse cameras, based on their elevation and the hypsometry of the glacier. I do not understand if and how the 10 mass balance stakes are used to help constrain the extrapolation to the whole glacier, especially the 7 stakes which are not located near the cameras. I do not see anywhere that reports the mass balance derived from all of the stakes, which are presented in the map of the study site (Fig. 1d). The differences in mass balance retrieved at the three cameras, shown in Figure 6, highlight the large mass balance variability with elevation, which is not necessarily linear. Therefore, I am wondering how this simplified extrapolation affects the glacier-wide mass balance results and the results of the study in general. The three locations will have different sensitivity to the heatwaves, depending on the baseline temperature and its proximity to the freezing point. The relevance of avalanches and other re-distribution processes is not mentioned or discussed and the authors do not subsequently consider any of the uncertainties in their main results when citing key numbers. 
4. The role of precipitation phase and surface albedo changes in glacier mass balance sensitivity is neglected: Figure 6 shows the derived daily glacier-wide mass balance and the time series of precipitation recorded at the nearby automatic weather station. The agreement in timing between precipitation events and increases in glacier mass balance can be clearly seen from the figure. However, it is unfortunate that little attention is paid in the manuscript to precipitation type, especially considering that snowfall replenishment and albedo reset are suggested to play a key role in glacier mass losses (e.g. lines 278-281). Summer snowfall will be a function of precipitation and air temperature, and I expect substantial differences along the altitudinal gradient of the glacier, which is not apparent, as most of the latter analyses in the manuscript focus on glacier-wide mass balances. I would suggest that the authors look at precipitation phase types, leveraging their meteorological observations and applying simple phase partitioning schemes such as dual-temperature thresholds or wet-bulb based parametrizations (Ding et al. 2014), to look at the amount of seasonal snowfall for each hydrological year and per elevation, and include this as part of the discussion on the inter-annual variability of glacier mass balance and sensitivity to heatwaves.
   
   The authors highlight the role of surface albedo on ablation rates, with the example of the 3rd period of heatwave in 2022 experiencing similar melt rates as earlier heatwaves despite lower air temperatures, likely due to darker surface conditions. With daily photos available for the three sites, it could be worthwhile examining the number of days per summer with bare-ice/darker albedo conditions, and linking this, even qualitatively, to ablation rates.
5. Redundancy and lack of clarity in figures: Figure 2 presents the methodology of the automatic extraction of height changes from time-lapse photography, but could be completed with a scheme or additional indications to help the reader visualize the different lengths introduced in the methods (L, Lp, Lpv, Lpa), making this section easier to follow.
   
   Figures 3 to 6 are somewhat redundant, showing the daily evolution of surface changes at the cameras’ locations in various ways and units. I do not think Figure 4 adds much to the manuscript; it is mostly an overlay of Figure 3’s content, and the inter-annual differences can already be seen clearly in Figure 6.  
6. Clarity of the structure of the manuscript: A substantial part of the manuscript introduces the set-up used to monitor glacier mass balances. The daily mass changes derived from time-lapse imagery are presented in the methods, but they could equally be shown in the results section. While both options would probably be fine, an outline of the paper’s structure could be given at the end of the introduction, which is commonly done to guide the reader through the paper.

Minor comments

- Title: “In-situ Measurements” is quite broad, especially since Time-lapse photography can be considered as one of the in-situ measurements. Consider replacing it with something more specific (e.g., meteorological observations) or remove.

-  Line 15: “anomalous less changes” is unclear and should be re-formulated. Anomalously less negative mass balances?

- Line 17: scarcity of high resolution observations of what? What resolution? Please clarify and state more specifically.

- Line 18: “the heatwaves”, remove “the” if you do not specify which heatwaves are referred to here. Line 20: “2019-2000” is probably a typo.

- Line 19: there are no meteorological observations at the glacier itself. Rephrase.

-  Line 21: “Observations evidence” ->  “Observations show”

-Line 24: The concept of the glacier loss day is not yet a widely-adopted term and should be avoided for the abstract and rather be clearly stated what it means. 

- Line 25: spelling (“wakened” -> “weakened”) 

- Line 27: Are there any glaciers not sensitive to heatwaves?

- Line 27-28: A strong mass balance response to a single year with heatwaves cannot be used alone to suggest the end of the regional anomaly that is decadal or multi-decadal. Please remove or rephrase to be precise about what it can show/suggest. 

- Line 46-47: Specify “in this region”. 

- Line 50: remove “s” from “for examples”.

- Line 54: The Oliver et al. reference describes marine heatwaves and is not really appropriate (also in the discussion). The authors should try and provide some numbers for heatwaves in High Mountain Asia. Here they describe extreme events in general, but this can also be precipitation extremes, snow accumulation extremes or others that can affect glaciers. Please be specific regarding the characterisation of heatwaves in the region, or clarify that no such data/studies are available if that is the case.

- Line 63: Remove “d” from “Characterized”.

: Line 65-66: State clearly the research questions/hypotheses of the study here. 

- Line 67: “Study regions” -> “Study region”.

- Line 73: Any reference for this value of 70 mm of annual precipitation? From the AWS? It seems quite low (under-catch corrected?) and appears wholly inconsistent when compared to the accumulation values given later on in the manuscript.

- Line 77: Are there no geodetic estimates of Hugonnet et al. (2021) for the specific glacier?  

-  Line 84: You could specify the date and time at which the photo was taken

- Line 92: “900 kg/m3”, any justification or citation for this value? Why not follow the common values of the literature with uncertainty ranges?

Line 96-105: Can the authors provide information about the distance to the stake from the camera and the resultant pixel resolution?

- Line 106: spelling mistake (“height, not “hight”). Here and in several places (Line 150 etc). Please revise and check carefully throughout the manuscript.

- Line 143: “0.18 cm” reads like a very precise number. Make sure that you don’t give numbers with a number of digits that goes beyond the precision achieved by your detection method.

- Line 152: How was the surface condition classified (snow vs ice)? 

-  Line 155: Do you have any justifications for the upper and lower bounds of snow density assumed? Could fresh snow fallen during very cold temperatures not have a density lower than 300 kg/m^3?

- Line 159: Can you be more explicit regarding what “lower” glacier mass changes mean here? Does it mean less negative, more negative, or less positive?

-  Line 160: “-409.02 mm w.e.”, cf. comment above, I do not think the precision of your mass changes derived from the camera is higher than 1 mm. Consider changing to “-409 mm w.e.”.

- Line 165: I am not sure if a website link is acceptable, do you have a proper reference for the digital elevation model used?

- Line 166: What about avalanches? Are they common on this glacier? Are these stakes really representative of those entire elevation bands? Following the major comment above, this needs to be critically considered when deriving uncertainties and at the very least, be discussed. 

- Line 167-168: Please clarify how the gaps were filled, as it is not clear from the description here in the manuscript. 

- Line 180: Are these solid and liquid precipitation, or only liquid precipitation?

- Line 196: How can the authors assert the role of sublimation from camera data alone at such a temporal resolution? Estimating sublimation requires specific measurements and modelling to characterize well. 

- Line 199: Explain what the ranges of value refer to. Are these the minimum and maximum annual values?

- Line 209-210: Unclear. There are losses from the surface earlier in the season than the start of June (cf. Figure 6). 

- Line 213: specify the years corresponding to each value of the range “-400 to 957 mm” given.

- Line 219: “thermal conditions” -> “air temperature”. To avoid confusion with the ice temperature.

- Line 231: How does this interpolation compare to the additional stake data that do not have cameras (see major comment)? Is this the same evaluation that is described earlier in the manuscript (lines 140-145)?

-  Line 240: The highest what? Be specific.

- Line 267-268: “Mass loss intensity […] was even greater than those during the two July heatwaves” -> This does not seem to be consistent with the numbers given in the last column of Table 1, please check this.

- Line 269: Spelling error for “Given”.

- Line 269: What is meant by “reduced atmospheric radiations?” Shortwave? Clarify and write clearly and precisely. 

- Line 269-271: Figure S2 actually shows fewer ice exposures during this year compared to 2022/2023. How can the authors reconcile this with their suggestion of albedo being the main driver (cf. line 279-281)?

- Line 277: A range of 100 mm is substantial for the region, but again this number and the range is notably larger than the value reported earlier in the manuscript. Please clarify those differences.

- Line 278: How can the precipitation amounts not explain the differences? How specifically was this tested? Do the authors simply refer to the relationship in Figure 10? What about antecedent conditions and precipitation in the month prior? Once more, the focus falls on heatwaves, but one year and ~3 months of the analysis see heatwaves, whereas the discussion of the paper talks more broadly about the anomalous glacier region and how this might support the end of the anomaly. Ultimately, more care is required in assessing the related role of precipitation and snowfall. 

- Line 304-305. This is a key statement, but make sure you keep here the link between accumulation variability during the accumulation period and the mass losses in the ablation season. The surface albedo changes will be a function of the seasonal snowpack height, such that the ablation rates are also linked to differences in accumulation (again related to the previous point and the major comment). Also, how have these contribution percentages been calculated?

- Line 290: How do glaciers initiate snow accumulation? Please reword. 

- Lines 306-313. This reads like a result sentence; consider moving to the result section.

- Lien 317: Spelling - “stereo” - “analyse”

- Line 319: 2022 was a positive year from the results of Falaschi? This is then in disagreement with the strong negative mass balances reported by this study therefore? Please clarify how the studies compare and elaborate on the reasoning for any strong contrasts.

- Line 342: The high glacier mass loss during the 2022 heatwave was also reported further west in the Pamirs (Jouberton et al. 2025).

- Line 364: Anticyclone “development”

- Line 376: What are “regional glaciers”? Please rewrite.

- Line 377: Again what is the role of accumulation regimes within this context of heatwaves and how does this compare with other studies on the sensitivity of glaciers in the region to temperature vs. precipitation? The summer of 2022 also followed a period of anomalously low snow accumulation (April 2022), similar to the European winter of 2021/2022. How much influence did that have?

- Line 378: What is extreme sensitivity? Relative to what? How/when are glaciers not sensitive to heatwaves? The authors need to be more precise and more scientific in their writing. 

- Line 381-383: This is clearer than what is written in the abstract, but still requires more substantiation in the manuscript. Where do we see evidence of increasing frequency of extreme weather in the East Pamir in the manuscript? Extreme in what sense? Only in heatwaves? Where is the evidence of this and are there any longer term mass balance data that can aid this interpretation of temperature changes and extremes driving this “transition”?

Figures

-  Figure 1: Consider replacing the studied area symbol by a more visible marker like a star or a triangle. It is a bit difficult to see in Figure 1a.

- Figure 3: The legend could be misleading, as “manual” could be mistaken as a measurement done by a person physically on-site. Consider expanding the legend as “camera: automatic”, “camera: manual”, or similar.

-   Figure 4: missing a legend for the shaded areas in the figure background.

- Figure 5: Consider using different scales for the three sub-panels to increase the readability of daily accumulations in the upper two panels. Alternatively, have you perhaps tried to overlay the three curves with different colors in a single panel?

- Figure 6: Write in the legend the meaning of the shaded areas around the mass balance lines.

- Figure 8: In the caption, precisely state that the data shown in panels a-c comes from the AWS.

- Figure 10: Any reason why the y-axis corresponding to precipitation is reversed? It might be more intuitive to have it the other way around.

- Figure 11. This is a nice addition to your locally derived results, but it is unclear what the anomaly is relative to. Please clarify. I would recommend swapping the colorbar of Panel d, such that the red colors correspond to higher melt conditions, as in the other three panels. Legend: Please specify the sources of the black outlines.

References used in this report

Ding, B., Yang, K., Qin, J., Wang, L., Chen, Y., & He, X. (2014). The dependence of precipitation types on surface elevation and meteorological conditions and its parameterization. Journal of Hydrology, 513, 154–163. https://doi.org/10.1016/j.jhydrol.2014.03.038

Farinotti, D., Immerzeel, W. W., de Kok, R. J., Quincey, D. J., & Dehecq, A. (2020). Manifestations and mechanisms of the Karakoram glacier Anomaly. Nature Geoscience 2020 13:1, 13(1), 8–16. https://doi.org/10.1038/s41561-019-0513-5



Hugonnet, R., McNabb, R., Berthier, E., Menounos, B., Nuth, C., Girod, L., Farinotti, D., Huss, M., Dussaillant, I., Brun, F., & Kääb, A. (2021). Accelerated global glacier mass loss in the early twenty-first century. Nature, 592(7856), 726–731. https://doi.org/10.1038/s41586-021-03436-z

Jouberton, A., Shaw, T. E., Miles, E., Kneib, M., Fugger, S., Buri, P., McCarthy, M., Kayumov, A., Navruzshoev, H., Halimov, A., Kabutov, K., Homidov, F., & Pellicciotti, F. (2025). Snowfall decrease in recent years undermines glacier health and meltwater resources in the Northwestern Pamirs. Communications Earth & Environment, 6(1), 691. https://doi.org/10.1038/s43247-025-02611-8 

de Kok, R. J., Tuinenburg, O. A., Bonekamp, P. N. J., & Immerzeel, W. W. (2018). Irrigation as a Potential Driver for Anomalous Glacier Behavior in High Mountain Asia. Geophysical Research Letters, 45(4), 2047–2054. https://doi.org/10.1002/2017GL076158