the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 26 Feb 2025
Brief communication: Impact of mountain glaciers on regional hydroclimate
Abstract. The crucial role of glaciers as a water supply underscores the need to reliably simulate alpine climate change, including glacier-atmosphere interactions. The presence of a glacier can change precipitation by generating mountain-valley scale flows, but we show here that their impacts on the atmosphere are more profound and much larger in scale. In a validated regional climate model, modest changes to the size of glacier termini in the Karakoram altered the large-scale summer monsoonal circulation, producing precipitation anomalies of sufficient magnitude and scale to overwhelm valley-scale orographic effects. Notably, the robust synoptic-scale moisture flow response exerted a substantial influence on precipitation and overwhelmed the localized response of the orographic flows, highlighting the significant impact of glacier ice on the monsoonal circulation and, hence, precipitation. These changes in turn impact glacier mass balance over the Karakoram range, emphasizing the importance of proper specification of glaciated area for the study of hydroclimate monitoring.
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RC1: 'Further analysis and more robust statements are necessary', Anonymous Referee #1, 04 Mar 2025
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In this manuscript, the authors present glacier-atmosphere interactions over the Karakoram range in High Mountain Asia. They employ a high-resolution modeling set-up with the WRF model, where they adjust the glacier termini (i.e., glacier tongues) to a more realistic representation. The impact of these adjusted ice surfaces is then analyzed, where impacts on circulation patterns and precipitation sums are found. The manuscript discusses an emerging topic in glacier-atmosphere interactions, i.e. the impact of the changed ice surfaces on atmospheric circulations. However, the manuscript seems to be somewhat unfinished, but despite this, the authors draw very bold conclusions, and many of these conclusions are not based on data they show, but rather read like speculation. To reduce these weaknesses in the manuscript, the results should be put into context, i.e., by presenting absolute precipitation sums, improving the description of which processes are at play. Furthermore, some more robust conclusions could be drawn if the authors would analyze their 6-month simulation dataset instead of only one month (July). The manuscript is not suitable for publication in The Cryosphere in its current form. However, I would like to encourage the authors to resubmit the manuscript in an improved form after thorough re-organization and re-writing.
Major comments
- The question of scales: You mention the "valley scale", "larger-scale", "synoptic scale", and "regional scale" (e.g., in lines 32-35). Could you provide actual values for these length scales based on your work, or a reference where this is defined?
- Figure 2: I am aware that the 'brief communications' category in TC allow for (only) three figures. However, I do not see the benefit of Figure 2. The left panel "only" shows the topography pf domain 3 (yes, we get it, it's high resolution), and the right panel shows the same information as Figure 1c. Given the restricted number of Figures, I would suggest to remove Figure 2 and rather focus on the results of your study with a potential new Figure.
- Figure 3 and the conclusions drawn: This Figure serves as the base for the results and conclusions drawn in the manuscript. However, as I outline in the minor comments below, many findings from this Figure are speculative and/or no supported by the data presented. There is room for improvement of this graph, as suggested below. Furthermore, the presented changes patterns and precipitation sums due to the changed ice surfaces only make sense if you put them into context, e.g., how high are the absolute precipitation sums over the region in July? You could create a domain average to show this. Furthermore, given the Figure, it is entirely unclear whether you talk about the thermally-induced flows, dynamical forcing, or both (and their interactions). Perhaps it would make sense to pick one of the glaciers from the cross-sections in Figure 3a and plot time series of wind speed and direction to highlight the shift in wind patterns. Moisture convergence: How sure are you that these are due to mountain waves and not only some (numerical) artifacts produced by the model?
- Chosen time period: If I understand it right, the authors conducted these simulations for half a year, but only show the month of July. Why? Analyzing half a year of simulations would allow for more robust conclusions? Would it make sense to extend the analysis from July to the six-month period and then add a new additional figure on the changed in precipitation sums and circulation patterns?
Minor comments
- l20: "cold surfaces and higher albedo" [..]: "cold surfaces and higher albedo compared to their immediate environment"
- l23: At this point, two pre-prints are worth mentioning, where ice surfaces are changed in the WRF model:Â
- Goger et al, 2024, EGUsphere (accepted for Weather Clim Dyn) https://doi.org/10.5194/egusphere-2024-2634
- Haualand et al, 2024, ESS Open Archive, https://doi.org/10.22541/essoar.172926901.19613096/v1
Furthermore, observational studies by Shaw et al highlight the impact of shrinking glaciers on the thermally-induced wind system:Â
- Shaw et al, 2023, GRL, https://doi.org/10.1029/2023GL103043
- Shaw et al, 2024, JGR Atmospheres, https://doi.org/10.1029/2023JD040214
and work on the impact of ice surfaces on mesoscale flows:
- Jonassen et al, 2024, QJRMS, https://doi.org/10.1002/qj.2302
- l25: "glaciers generate mountain-valley scale flows": Please be more precise. Do you mean thermally or dynamically-induced flows? Do you only mean the katabatic down-glacier wind or its interaction with other flows as well?
- l40: "large mountain ranges": Which mountain ranges do you mean? Are, e.g., the Alps (subject of the mentioned studies) not a large mountain range in your definition?
- l43: Remove brackets from the reference
- l55: "pixels defined regional climate models" I agree, but this is mainly due to poor resolution in land-use datasets utilized by these models
- l59: Reference Fig.1c
- l60: 'extremely low compared to other regions': By how much?
- l70: "default land use": It is necessary that you mention and cite your source for the land use dataset used for your model configuration.
- l71: If you improve the glacier termini, it actually results in a more realistic picture? I am not sure why you use the term "idealized"
- l74: First, "anomalies" usually refer to a difference from a norm, but in your case, you actually improve the glacier representation in your domain, therefore, I would suggest that you call it "differences". Furthermore, you call it "thermally-induced flow". How do you know that all of the changes in your flow patterns are thermally-induced in an average over an entire month?
- l80: "reflecting synoptic-scale shifts" [...]: unfortunately, this sounds like poor speculation. Precipitation patterns over complex topography can be very localized, because local thermally-induced circulations strongly impact updrafts and convection (e.g., Kirshbaum et al, 2018 https://doi.org/10.3390/atmos9030080, and Goebel et al, 2023, https://doi.org/10.5194/wcd-4-725-2023). A few paragraphs before, the authors even mention the shift in local mountain-valley circulations. This shift can be also responsible for your changed precipitation sums and moisture convergence, even without the impact of the synoptic-scale flow.Â
In the next sentence, you mention that "synoptic scale flows overwhelmed local circulations". Where do you see this? Since you have your model output data, you could provide additional analysis to support this claim. - l84: "prominent imprint of mountain waves": Now the authors mention mountain waves, in contradiction to their initial statement above, that mostly thermally-induced flows are present. Mountain waves are excited to to large-scale forcing. How can thermally-induced flows persist when mountain waves are dominating?
- l86: "impact of glacier ice on the monsoonal circulation": This is a very bold statement - as the authors mentioned one sentence beforehand, the large-scale monsoon circulation alters the local forcing.
- l86: "superimpose" Please reformulate.
- l107: "modifies the surface wind pattern": You do not show surface winds anywhere. You only shows changed wind patterns in one single cross-section.
- l 109: "This indicates the enhancement of the katabatic winds, often referred to as glacier winds, due to the presence of valley glaciers" Large-scale flows do not per se enhance katabatic glacier winds. This depends on multiple factors, including the synoptic flow direction (Goger et al, 2022, https://doi.org/10.1002/qj.4263). As shown in the aforementioned study, large-scale flows might indeed erode katabatic flows, and henceforth reduce their strength/impact.
- l110:"Additionally, the precipitation response pattern is dominated by synoptic-scale features that overwhelm the effects of the valley-scale anomalous circulations." This sounds agreeable, but the authors describe something else in the results (e.g., line 86).Â
Figures
- Fig3: Why do you choose exactly this cross-section?
- Fig3a,c,d: plot/add topography. This might explain some of the patterns.
- Fig3b: This graph is not so easy to understand. What exactly do the wind arrows represent? Does it really make sense to average wind patterns over an entire month int this complex topography?
- Fig3: Labels for all colorbars are missing.
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Citation: https://doi.org/10.5194/egusphere-2025-675-RC1 -
RC2: 'Comment on egusphere-2025-675', Anonymous Referee #2, 06 Mar 2025
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General comment
The authors have conducted a sensitivity experiment considering local-scale snow and ice distribution in the valleys of the Karakoram region, comparing it with a control experiment that does not account for such distribution. Their key finding suggests that incorporating local-scale snow and ice distribution modifies local-scale circulation associated with mountain-valley topography and further influences synoptic-scale monsoonal circulation and precipitation. Understanding the upscaling effects of local glacier distribution on large-scale atmospheric circulation is an important research topic. However, the current version of the manuscript does not yet fully achieve its objective. The presented figures are insufficient to support the authors’ conclusions, and additional, more detailed analysis is necessary before publication.
Major comments
- Before discussing the sensitivity experiment results, the simulation output should be validated using in-situ and/or satellite-based observational datasets. While we acknowledge the limitations of observational data over high mountain regions, validation is an essential step to ensure the reliability of the simulated differences between the control and sensitivity experiments.
- The differences in precipitation and other variables between the two experiments, particularly in domain D02, seems to show chaotic noise. Please provide statistical significance testing to confirm whether these differences are meaningful.
- As described in Section 2, precipitation in the target region is influenced by both winter westerly disturbances and the summer monsoon. Why was the analysis limited to July? Does the upscaling impact of glaciers on atmospheric circulation occur in other seasons as well?
- Several conclusions described in the manuscript are not sufficiently supported by the presented figures. More comprehensive analysis, additional evidence, and substantial revisions are necessary to justify the authors’ claims.
Minor comment
L43 while (Collier et al., 2015) -> while Collier et al. (2015)
Citation: https://doi.org/10.5194/egusphere-2025-675-RC2
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