the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 27 Mar 2025
Swiss glacier mass loss during the 2022 drought: persistent streamflow contributions amid declining melt water volumes
Abstract. The year 2022 was extremely warm and dry in Europe, resulting in a severe hydrological drought. In Switzerland, part of Europe’s water tower, streamflow in glacier-fed rivers could have been even more reduced if the situation had not led simultaneously to extreme glacier melt. Here we analyze the role of glaciers during the 2022 drought for 88 glacierized catchments by combining streamflow and meteorological observations with estimations of snow water equivalent, actual evapotranspiration and daily glacier storage changes. We also compared the year 2022 to earlier exceptionally warm and dry years (1921, 1928, 1947, 1998, 2003 and 2018) to assess if the ongoing glacier retreat has already caused a declining meltwater supply in such extreme conditions. Results show that 60–80 % of the total glacier melt in 2022 came from net mass loss (imbalanced melt). During summer, the increased melt could completely offset the precipitation and snowmelt deficits for catchments with around 15 % glacierization. Further downstream, the extra melt in summer alleviated water input deficits by up to 5 % at Basel (Rhine) and 70 % at Porte du Scex (Rhone). However, compared to other extreme years in the past, total melt volume has been noticeably declining due to a strong reduction in glacier area – despite more extreme melt rates per unit glacier area. In contrast, the relative contribution of glacier melt to streamflow stayed constant or even increased for some months, suggesting that glacier melt remains important during droughts. Comparing 2022 to 2003 –the most comparable recent extreme summer– shows a declining glacier meltwater supply for 55 % of the catchments during summer and 36 % during July, despite more intense melt, with the difference in summer/July reflecting the extremeness of the melt conditions, counterbalancing the reduction in glacier area. This declining meltwater supply raises concerns for future drought situations.
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RC1: 'Comment on egusphere-2025-404', Anonymous Referee #1, 05 May 2025
Dear authors,
please find attached a PDF with detailled comments.
I see the paper, with its focus on the buffering role of glaciers on streamflow in the 2022 extreme event, as important and meaningful contribution to a wide audience. The paper is well-structured and provides a huge and comprehensive amount of information across the Switzerland and a wide set of variables and plots are already well-thought and presented. Nevertheless, I think the manuscript could be further improved and clarified, not only content-wise but also language-wise. I had the impression that some descriptions and explanations of the plots could be improved and are rather vague or not precise enough making it hard to get an idea to which of the many details in the plots the authors are referring to. This facilitates misinterpretation and the mixing of numbers.
The major comments you will find in the attached PDF refer to:
- some major methodological clarifications that are necessary for the readability and comprehensibility (especially the glacier mass balance interpolation and adjustment). A flowchart like Fig. S2 is highly needed in the main text for the flow of the paper.
- stronger focus on the hydro-meteorological conditions (also better represented in the main text rather than in the appendix) with some spatially-distributed water balance anomaly information
- more emphasis on the methodological & dataset decisions and thus the error term provided in the context of the glacier compensation introduction
- weaknesses in the presentation of 5.4
- recommendations for extensions/replacements
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AC1: 'Reply on RC1', Marit Van Tiel, 18 Jul 2025
We thank the reviewer for their time and effort in evaluating our manuscript, for acknowledging the quality of our work, and for providing constructive comments and suggestions. Please find our detailed responses to the comments in the attached document.
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RC2: 'Comment on egusphere-2025-404', Anonymous Referee #2, 18 May 2025
The author investigated the driving factors for streamflow changes during the 2022 drought in Switzerland. I enjoyed reading this paper. Glacier melting has accelerated in recent years, raising a key question: Will peak runoff arrive by the middle of this century? The author illustrated that enhanced glacier melt may not compensate for reduced glacier area, potentially leading to decreased glacier runoff in the future. The paper is well-written and well-structured, except for the results section, which could be more conclusive. My major concerns relate to data quality control. It would be valuable to include one or several basins with robust in situ observations to support the study’s conclusions. I recommend minor revisions before considering publication. Specific comments are listed below:
Line 15: “with the difference in summer/July reflecting the extremeness of the melt conditions.” This is not entirely clear to me. Could you clarify what “extremeness” refers to in this context?
Line 100: Can you explain why 25% was chosen as the threshold? “If the ratio exceeded 1 and the catchment was classified as 100% natural, we applied a uniform multiplication correction to the daily precipitation data.” The bias in observed precipitation depends on gauge type and varies across seasons. If the bias primarily stems from winter under-catch, glacier accumulation could be significantly underestimated. The author briefly addressed this in Section 5.3 and the discussion. It would be interesting to include more analysis based on in-situ observations, such as comparing winter glacier mass balance (GMB) with observed winter precipitation to check if biases are consistent across years. In general, the data quality control section needs more explanation, as it directly impacts the results. A schematic illustrating this process would clarify the section.
Section 4.1: I like this method, but it could be described more clearly. Consider moving Figure S2 to the main text and incorporating the method or data preprocessing workflow into that figure.
Line 190: γ = 1.8. Does this value apply to all glaciers in the study region? This seems slightly high for glaciers in Switzerland.
Figure 2b: For contributions of the late ending of the melt season to ΔBs, why are the bottom whiskers invisible in the Rhine, Rhone, and Po basins compared to the Danube basin? This is particularly notable since the Po and Danube basins are geologically similar.
Figure 3: It would be interesting to include a figure with units in percentage, as the absolute values of these terms differ.
Line 320: “The relation between glacier melt contribution to streamflow and level of glacierization is exponential, showing a steep increase in melt contributions for catchments with 0–20% glacierization, which diminishes for catchments with more than 20% glacierization.” This is interesting, but do you have an explanation for this pattern? Be cautious with this conclusion, as I don’t see this trend in the reference period.
Figure 4: The comparison of uncertainty ranges between different groups is unclear and seems unfair. Due to the logarithmic scale, the uncertainty for highly glaciated basins appears much smaller than for others.
Line 365: Do you have any data to support this aspect?
Line 375: Could you add a definition of “changing sensitivity”? Consider moving the sentence from Line 420 to this section.
Figure 8, Panel B: Why do glacier area changes appear almost linear after the 1970s? How was the initialization of the glacier state handled in the modeling?
Section 6.2: As mentioned earlier, providing more in-situ data in the supporting information would be beneficial. This method could also be applied to other mountain regions globally.
Line 450: Out of curiosity, what method was used to measure discharge in Switzerland?
Citation: https://doi.org/10.5194/egusphere-2025-404-RC2 -
AC2: 'Reply on RC2', Marit Van Tiel, 18 Jul 2025
We thank the reviewer for their time and effort in evaluating our manuscript, for acknowledging the quality of our work, and for providing constructive comments and suggestions. Please find our detailed responses to the comments in the attached document.
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AC2: 'Reply on RC2', Marit Van Tiel, 18 Jul 2025
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