the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Quantifying the hydrological disturbances induced by snow grooming and snowmaking in ski resorts: a case study in the French Alps
Hugues François
Marion Réveillet
Eric Sauquet
Louise Crochemore
Flora Branger
Etiene Leblois
Marie Dumont
Abstract. The presence of a ski resort modifies the snow cover at the local scale, due to snow management practices on ski slopes, especially grooming and snowmaking, which affect the quantity and physical behavior of the snowpack. Snow management exerts two-fold disturbances to the local hydrological cycle, through (i) uptake of water used for snowmaking, either directly after uptake or following temporary storage and (ii) changes in water runoff due to added snow mass through snowmaking and/or delayed melting of the snowpack due to snow grooming. This induces a local pressure on water resources that can be substantial in places and fuels controversies regarding the environmental impact of ski resorts. However, no scientific study to date has quantified the quantitative and qualitative disruption of the local hydrological cycle downstream, concerning both the modification of the local seasonality of the flows (e.g. low water periods) and possible modifications of the volume of water returned. Here we describe results from a case study quantifying the various components of the water budget of a small catchment (several km2), partly covered by a ski resort, in the Northern French Alps. Snow cover simulations, including the timing and amount of snowmelt, were performed using the Crocus snow cover model driven by the SAFRAN reanalysis and future climate scenarios, with and without accounting for grooming and snowmaking. Our study demonstrates a visible impact of snow grooming, through the quasi-suppression of winter snowmelt, leading to delayed snowmelt onset. Snowmaking leads to additional snowmelt amount, of the order of a few percent at the scale of the catchment, scaling with the fraction of the catchment covered by ski pistes, and the fraction of the ski pistes equipped with snowmaking. Under the situation of the case studied, there is no substantial further water loss due to snowmaking after the snow production itself, which induces about 10 % of evaporative loss of water used for snowmaking, related to the snow production process. Snowmaking mainly leads to a moderate shift in snow cover formation and snowmelt processes, to a smaller degree than the influence of future climate change on mountain hydrology. This study provides quantitative estimates of the impact of grooming and snowmaking on the hydrological regime of mountain catchments interesected by ski resorts, which can inform further studies addressing water management and climate change adaptation in mountain regions harbouring ski tourism infrastructure.
Samuel Morin et al.
Status: final response (author comments only)
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RC1: 'Comment on egusphere-2022-1186', Anonymous Referee #1, 03 Dec 2022
General comments:
The paper addresses a relevant scientific question which is within the scope of HESS. It is attempted to quantify the effect of grooming and technical snow production on the water balance components in a Northern French skiing area by means of a combined physically based modelling experiment. In this comparably narrow scientific field the study is probably the first of its type and it does present novel ideas and data.
In general, this is a very valuable and novel contribution in this field. It could however profit from a sound explanation of the choice of the presented methodology.
The original approach of the coupled models has obviously been developed for large scale applications, but is applied here at the local scale of a single ski resort. This resulting scale gap requires several regionalization steps and assumptions which might be the cause for manyfold uncertainties. A sound argumentation should be presented why concepts are chosen like „gravitational envelopes“, „Ski resorts Representative Units“ or „SAFRAN altitude bands …“ (and adopted from the Vanoise massif, some distance away). The spatial units are „intersected“ by the ski pistes with or without their snowmaking equipment (requiring water fluxes scaling afterwards), and/or „crossed“ by the slopes. Even though the original literature where these concepts are described is presented, it mostly remains unclear why the given set of methods is appropriate, and why not a method is applied which uses local measurements and reproduces the water fluxes at the local scale.
The results indicate that the hydrological effect of grooming/snowmaking is small. To which degree are these results caused by uncertainties of the CROCUS simulations? This question arises since for the latter a set of assumptions is applied which significantly might affect the magnitude and timing of the computed water fluxes (mainly with regard to snowmaking practice, initial water loss and available water amount). Another source of uncertainty is probably the model forcing at the SRU scale, since the chosen method does not account for the conditions at the location of the snow guns and lances. Ski resorts applying technical snowmaking usually monitor and save the available water storage volume and fluxes used for the snow production, so this data should be available.
Two catchments are introduced, one of which is ungauged and requires a spatial transfer method, and generally „information on hydrology is rather sparse“. Hence, several simplifying hypotheses are formulated. Is it possile to evaluate the effect of these hypotheses at the local scale where measurements are available? If the approach remains „purely empirical“: could it be replaced by a much simpler, but easier to understand estimation?
The overall presentation of the paper is well structured and the authors give proper credits to related work. The abstract would benefit from a more complete presentation of the most important results. The choice and number of references is adequate.
Specific comments:
- some terms used are not very common in hydrology (e.g. „disturbances“, „disruption“, „behaviour“, „alteration“). I recommend to change the title accordingly, and also choose other terms in the text
- the analysis of the climate change effects is of limited explanatory power, since only climate is considered. However, many other influencing fators - hard to predict, though - will change and develop in parallel to the climate. It is not so clear if the conciseness of the paper profits from this section
- „water reaching the soil“: to which degree is this a suitable hydrological variable for hydrological change? It can affect streamflow amount and timing at the catchment outlet in very different ways, depending on the hydrological characteristics of the catchment. Maybe one could still add a simple consideration to relate water amounts to streamflow regime, as announced in the text?
- is mechanical stress caused by the skiers and its effect on the snow surface considered in the simulations?
- does SAFRAN provide humidity? How is wet bulb temperature derived?
- technical snow is rather different than natural snow. On the slopes with snowmaking, a mixture of the two develops over the season with varying composition and hence changing physical properties at the surface. Does CROCUS account for that?
Technical corrections:
- figures should be larger
- the English language could profit from correction by a native speaker (mainly: uses of articles, and singular/plural)
- better explain the basic functioning of HydroDem explicitely, rather than referencing another software (TauDem)
Congratulation to this work and valuable contribution! I hope my comments support the further improvement of the manuscript.
Citation: https://doi.org/10.5194/egusphere-2022-1186-RC1 -
RC2: 'Comment on egusphere-2022-1186', Anonymous Referee #2, 25 Feb 2023
Morin et al. present a very interesting study on the hydrological implications of snow grooming and snowmaking in the French Alps. Despite being a frequent practice, such studies are rare and our hydrological understanding is limited. To achieve this goal, they implemented a snow model (Crocus) for a ski resort and compare simulations with or without grooming and snowmaking. They found that the influence of such techniques on the hydrological cycle is significant at slope scale, while it expectedly decreases when looking at larger scales.
Overall, the study is interesting and novel and I am in favor of publication. At the same time, it presents some points that should be better discussed, especially for the fact that the paper aims to discuss hydrological implications but no full-scale hydrological model was implemented. Authors openly discuss this, but at the same time some conclusions related to the impact of ski-resort procedures on the hydrological cycle should be refined in this sense (see below).
SPECIFIC COMMENTS:
- The abstract reads quite qualitative at places, and I would recommend being more specific and quantitative. For example: “several km2” (please report the exact extent and location); “visible impact” (please quantify this); “few percent” & “additional snowmelt amount” (same, please quantify this);
- Introduction: I missed specific research questions and/or hypotheses that authors want to explore. The overall goal of the research is clear, but the lack of specific research questions makes the flow of the paper a bit difficult to follow. Also, please consider breaking this section into paragraphs for readability;
-Line 82: could you please elaborate a bit more on these “deviations”?
- Section 2.3: the concepts of SRUs and gravitational envelopes are interesting, but also a bit hard to grasp for readers like me that are not familiar with this particular field of study. How do SRUs exactly differ from hydrological response units? My understanding is that they are found intersecting elevation and aspect of ski slopes with location of snowmaking equipment, but this was a bit too concise. Same for the gravitational envelope concept. Perhaps a schematic might help here?
- Section 2.4: could you elaborate a bit more on the adjustment method used (is it a bias correction?) and perhaps spend a few words on the S2M reanalysis?
-Figure 2: please consider adding a small panel with the location of this resort in France;
- Results: please consider summarizing section titles, which are quite long at the moment
- Section 3.3 (comment #1): while the discussion of snow simulations was very clear, relevant, and interesting, I got a bit lost in this section about the catchment scale. My main issue was that I didn’t quite understand how authors combined the different sources of information, and how these sources of information interacted with each other to solve the overall water balance and so derive Figures 6 and 7. I would suggest the inclusion of a water balance equation where all terms are reported, so to understand how the impact of sky resort practice was quantified.
- Section 3.3 (comment #2): my understanding is that the various sources of data refer to significantly different periods, sometimes with no overlap (e.g., water resources data date back to the 40s-60s). Perhaps I am missing something here, but I would include a discussion on comparability of climate across the various periods, since water use and consumption can significantly change based on precipitation and temperature patterns. Also, are “water resources” streamflow measurements in the end?
- Line 280: what do you mean with “hides heterogeneity” here?
- Section 4.2: I agree with authors that evaporation losses during winter are small, and so snowmaking consumption is expected to be minimal in that regard. However, shifting snowmelt peak by weeks to months (as reported in Figure 5) implies that the bulk of snowmelt is mobilized at a time when transpiration by plants is much higher than in winter. Also infiltration patterns are very different from early spring to early summer, depending on soil thermal and moisture conditions. In this regard, this in-depth discussion on water management implications would benefit from some forms of hydrological modeling, or at least a quantification of the other components of the water balance (evapotranspiration and storage).
Citation: https://doi.org/10.5194/egusphere-2022-1186-RC2 -
RC3: 'Comment on egusphere-2022-1186', Anonymous Referee #3, 27 Feb 2023
The manuscript presents an assessment of the influence of snow management on water resources at a ski resort with heavy snow making. It is a very interesting topic, and while being very niche, of high interest to the recreation and ski resort management community. It is interesting to see how this study brings in physically-based snow simulations with water management assessments to find some insights on a relevant issue to the local community – it is novel, and innovative while being oriented towards water management issues. I overall enjoyed the manuscript and found it straightforward and interesting. I appreciated the clear discussion of the implication and limitations.
Overall, I would have liked more information about the snow production numbers – how often and how much ends up being made. This seems like an important aspect of the discussion, but it was glossed over. I would also have liked more context on the methods – why certain methods were chosen, and especially how the water supply and demands was classified in the hydrological assessment.
My main concern with the manuscript is the lack of model evaluation. The proposed results could be completely different from how snowpacks evolve in the area. Could the snow evolution presented in Fig4 be compared with satellite imagery of actual snow cover in the basin? Could the water supply (or streamflow) in Fig 6-7a be compared with the limited streamflow measured in the basin?
I also suggest an examination of the language to make sure the sentence structure is clear and without too many clauses. Some sentences are long, with many commas and additional information. It makes them hard to follow. I also suggest the authors try to use precise language throughout the manuscript (“several, a few, many, some, etc, … “could be replaced by the actual numbers or words). I also have many small comments to clarify some language used or some suggestions on the figures.
In-line comments:
L10 – Can you give the number instead of “several”?
L14 -Same thing – instead of saying “few percent” could you give the actual number?
L15 – This might be a tricky one, but in North America, we don’t call them piste – we refer to them as ski runs. Maybe something like a skiable area would be less regionally-dependant?
L80 – Wouldn’t wind fit in the atmospheric conditions? What do you mean by “etc”?
L123 – Can you add some information on this? What is the Vanoise massif – does this refer to the mountain range where La Plagne is, or the closest location with the forcings? What makes it representative or adapted or beneficial for your application?
Figure 1: If snowfall falls on the ground, it should go into the snowpack? I don’t quite understand how you can have a snowfall arrow on the snow-free ground. If it melts instantaneously, it would still be liquid water reaching the ground?
Also, do you ignore completely anything related to forest interception? The snowfall on the piste and off-piste will be quite different. This will not apply to comparing groomed and groomed+snowmaking, but it might apply when considering the sub-basin assessment, or the gravitational envelope assessment.
L133 – ref for the DEM DB-alti?
L136 – Why do you give a reference to taudem, but not to hydrodem? I am also not sure if comparing HydroDEM and taudem and mentioning that tauDEM is more well-known is relevant – arguably, different science communities will know one or the other better. You could mention if one is more recent than the other, or if one has different benefits or flaws, but I don’t think “well-known” is a solid argument. Also, you write it HydrodDem and HydroDEM. Please be consistent.
L141 – Can you specify the years instead of mentioning “previous years”
L145 – I understand that most of the information about the adjustment to the local scale is done like in Verfaillie paper, but could you add 1-2 sentences summarizing it here? It is an important step. Also, what is the spatial and temporal resolution of the GCM/RCM product? And, you mention that you take the result for RCP8.5 for 2043-2057, but then in L153, you mention that you use the values for the adjustment for 2090-2099? Could you please add some more information about these products and downscaling to help understand this manuscript?
L154 – I suggest removing “pending further investigation using a genuine ensemble for climate model simulations” and L149 “although this study does not address…”. I appreciate the honesty about the limitations of the products and study, but I suggest moving these mentions of limitations to a discussion section.
L158 – Could you give this value in km2 or m2?
L161 – Can you add a sentence about what a lance is?
Fig 2 – The colours for the elevation bands are hard to distinguish, especially with the hillside applied. If it is important to see the 300m elevation bands, I suggest having more distinctive colours. Otherwise, you could use a continuous gradual colour gradient map instead of a classification with 9 types. These maps with the Bonnegarde catchment come before any explanation of the Bonnegarde basin in the text. I suggest either moving the figure down or mentioning in the caption that Bonnegarde is the main studied sub-basin. I also don’t think you need to mention that you made the map. I also find Fig 2 and 3 somewhat redundant. Could you also put the Frasses basin on Fig 2a? or maybe merge Fig 2 and 3?
L177 (point 1.) – Could you add this point on Fig 3?
L185- Could you remove the “… “- either mention “such as industry, energy production irrigation) or give the full list.
Fig 3 – What are the small grey lines outside of the basin? The two small subbasin maps on the right (could you add a-b-c labels to your panels?) are not providing much new information and could maybe be removed, and then Fig 2-3 could be joined. For the easiness of map reading, could the basin outlines lines be made thicker? And the points and text? As you mention in the text, the local of BNPE cannot be put on the map exactly, but you have it on the map, which is misleading.
L192 - You don’t have a section about model evaluation?
L196 – You run the simulations for a much longer period – why do you show only 2019-2020 as an example? Have you considered doing the average of the period? Or explain why you only show 1 year of results.
L200 – I don’t quite follow how a higher thermal conductivity results in cooling – Here are you specifically talking about radiative cooling at night? Because then, wouldn’t the transfer of energy in the day, causing faster melt, also occur? Do you mean that the snowpack loses its insulation capacity over the ground? Also, if this is background knowledge that has been studied in previous literature, this description of how grooming influences sow behaviour should be in the introduction, and then could be further discussed in the discussion.
L207 – This also means that you neglect any kind of snow interception and sublimation by trees or blowing snow sublimation during a blizzard. I assume that a lot of the off-piste area is forested (as in Fig 2 ski area map) in the study area – how do you represent forest hydrology in the model? And how does it influence your results? You don’t mention the forest within the manuscript.
Section 3.4. – Could you provide a number relating to how much snowmaking occurs over the different years? in the methodology, you mention it could occur throughout the winter, but in the figure, it only occurs at the beginning of the season. Is this the case in all the simulations? Are the values for the 2019-2020 representative?
Fig 4 – same as the previous figure – make the text and line width larger so the figure is easier to read. In the caption, you say “La Plagne ski resorts” – is there more than 1 resort? (resort vs resorts?). You are also missing the word “year” for the hydrological year 2019-2020. Have you considered plotting the individual fluxes for each simulation instead (grouping per fluxes instead of per simulation?) I am mainly interested in how snowmelt changed between the simulations, and it is hard to see as they are on 3 different panels. The snowfall and rainfall lines are also redundant, as they don’t change between the simulations. And what are the vertical grey lines?
L240 – and the differences between the simulations here are highly overexaggerated as you consider the runs to be completely covered in snowmaking, compared to the 40% in reality.
L245 – Can you explain what you mean by empirical here? Do you mean it is a first-order estimate based on the limited information and modelled result?
L251: Do you mean ‘assumptions” – are these assumptions of how the basin behaves?
L258 – I don’t follow – where do the 6% and 30% values come from?
L262 – You use the hydrological estimates based on 100% of the ski runs being covered by snowmaking, but then you only apply the volume of snow made to the areas with snowmaking. This seems like a mismatch of approaches.
L245 to 262 are details regarding the methods and should be in the methods section, not the results.
L266 – You mention Fig 6-7 before table 1, but then table one comes first in the text. Please adjust either the text or the order of the figures.
L269 – Maybe add a bit more information about the results from table 1?
L277 – “for areas at high elevation” – this is confusing – what does this sentence clause refer to?
Fig 6-7: In the text, you keep presenting the result for Fig 6a-Fig7a, and Fig 6b-Fig7b, which forces the reader to go back and forth between the two figures. Could you either put the two figures side-by-side or maybe with bars side by side? Something to make the comparison easier?
I also don’t think it is okay to put the solid and liquid contribution in volume – the density between the snow and the liquid water is different enough that this comparison between snow production and grooming and the snowmaking effect (or other subpanels) is misleading. This should likely be transformed to liquid as well to take into account the difference in density.
Fig 6-7:
- By water resources, do you mean streamflow? The amount of water available in the river?
- The axis for e-f is missing a number.
- I am curious about your choice to start at week 31 - it splits your JJA into 2 sections and what the different colours represent (light blue, black, green, dark blue). And also, the figure is quite long, and it would be nice to have the weeks on the x-axis in more than one location to avoid having to always scroll back to the top.
- I find the classification of what is what in the subplot hard to follow. Fig 6-7b, you call it drinking water but in L272, when you mention the figure, you call it water supply? And for Fig 6c, you call it “abstraction for reservoir filling”, but in L279, when you refer to the subplot, you call it weekly water abstraction for snowmaking. I suggest working on this section so that there is a clear link between what the subplot refers to and the values that were obtained.
L280 – If it is misleading to aggregate reservoir volume across the basin, then I suggest you don’t present it as a result and instead show the variability between the reservoirs.
L320 -moderate? I think minimal, or very limited, might be a better description. It is a change of 0.22%...
L321 – The amount of snowmaking is bound by the model – meaning that snowmaking cannot be higher than a certain amount. Based on the criteria of the snowmaking processes (temperature, humidity and water availability), can snowmaking even occur? It might be more interesting to discuss how snowmaking abilities in the future might change. Would it need to occur later in the year due to temperature?
L322- mm3?
L325 – critical? Given the results presented here, which suggest a limited influence of snowmaking on water resources, this seems like a strong wording. “much-discussed” or “often debated” might be more accurate.
Figure 8: Monthly sums instead of monthly cumulative?
L325 – This first paragraph of the discussion does not bring any additional information. I suggest removing it and integrating this information either in the introduction or the conclusion.
L340 – You don’t present results relating to basal melt – just about the snowpack as a whole. If basal melting is the main process that is suppressed, and this is a key result, then it could be presented in a figure of natural snow melt fluxes vs groomed snow melt fluxes in the first result section about the point balance.
L375 – Could you write this as an equation? It might be cleaner than only in words. Also, this rule of thumb could be a result. Or a key discussion point on its own? You present a number here about snow production that would have been interesting in the results section, as I mentioned in some other comments. If the main dilemma for water supply is the use of water for snow production, then these numbers should be presented further and put in context.
L399 – Could you rephrase “a few %” to the actual number?
Section 4.2 : You don’t bring up here the fact that, based on your simulations, there is a difference between snowmaking and grooming for the ski runs, but there is such a small percentage of the basin, and with only a section of these being covered by snowmaking capabilities, that overall it makes a small difference – which is a key message I understood from your analysis – Fig 5b.
L421 – resort instead of resorts.
L427 – I feel like I missed that information! This is interesting.
LL428 – typo – at
L435 – The lack of evaluation data for your model should be a key point of your discussion, not one sentence in the conclusion. The entire manuscript is a modelling exercise that presents no comparison with reality. Which makes it very limited. I understand that by comparing groomed vs groomed+snowmaking, you avoid some of the complications linked to model evaluation, but you do still present a lot of results (snowpack evolution, water supply etc) that are not just the difference between simulations.
L439: I suggest removing this quotation from the IPCC and also rewording this final segment. You really focus on all the aspects of this study that you didn’t consider (which could be put in the limitation section of the discussion), which makes the paper end on a sad note. While this manuscript has a lot of limitations, you tried to quantify a water supply issue faced in mountain communities that is highly discussed and has local relevance. I suggest you should focus on having worked on that instead of on all the things you did not solve – and that are, as you mention, outside the scope of this manuscript.
Citation: https://doi.org/10.5194/egusphere-2022-1186-RC3
Samuel Morin et al.
Samuel Morin et al.
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