World of Science | Review ISSW2018: Snow hydrology, sustainability and climate change

This time: Snow hydrology, sustainability and climate change

This session has a comparatively broad thematic focus and covers a wide range of topics. While some contributions deal with large-scale changes in the snow cover and its hydrological characteristics, others go into great detail, for example with regard to special measurement methods or new modeling approaches. Sustainability in the usual sense is hardly discussed, but there are some somewhat out-of-place contributions that might have been better suited to other sessions.

Snow and climate change

Since 1880, the average temperature in the Alpine region has risen by 2°C - that is about twice as much as the global temperature increase over the same period. While the rising temperatures can be clearly seen in the measurement data and the modeling of future developments, there are significantly greater uncertainties when it comes to precipitation. At low and medium altitudes, precipitation is increasingly falling as rain instead of snow. At high altitudes, there are few clear trends in the amount of snow. Model results even suggest a slight increase in precipitation in certain regions, which would also lead to an increase in snow at sufficiently high altitudes (Gobiet et al., Climate Change in the Alps and its consequences for snow). So-called "rain on snow events" - rain that falls on an existing snow cover - are becoming more frequent, as it rains more often in winter up to high altitudes (Juras et al., Effect of snow cover on hydrological response during rain on snow events).

The effects of changes in snow cover are manifold: Long-term shifts in the snow-out or snow-in date, earlier snowmelt and/or lower snow depths, for example, are of great importance for the water balance of local and regional ecosystems (Wieser. The contribution of snowmelt to the annual waterbalance in the Tyrolean Alps). The seeds of certain plants sprout or not, depending on whether the ground is snow-covered, with corresponding implications for agricultural yields (Zhao et al., Effects of snow cover on seed germination for two species in Iron Mine Tailling, Cold Desert). If more snow is produced due to a lack of natural snow, the vegetation on the ski slopes changes ( Bacchiocchi et al., Sustainability of small ski resorts and ski slope management under climate change in South Tyrol)

Determining the actual state

Studies that deal less with the past or the future, but primarily with recording the actual state of the snow cover in different regions, are also strongly represented in the session. As we all know, this is no trivial undertaking either, and here too there are contributions that deal with measurement data on the one hand, model-focused work on the other, and of course combinations of both.

In Italy, large-scale data analysis is being used to determine what has always been thought anyway: The snow in the more maritime regions (Maritime Alps, Veneto, Julian Alps) is on average heavier and denser than the snow in the higher, drier areas further away from the sea (Valt et al, Snowcover density and SWE in the Italian Alps).

In Afghanistan, one can for the most part only dream of snow data measured on site. However, there are always large avalanches that cause damage to infrastructure and endanger settlements, which is why a rudimentary avalanche warning system based on satellite data and weather forecasts is important and useful for the affected communities. In this context, attempts are constantly being made to improve the modeling of snow water equivalent and other snow parameters and to calibrate the models with the few available measurement data (Hamilton Bair et al, Using machine learning and snow water equivalent reconstruction to predict today's SWE and avalanche conditions in Afghanistan).

Satellite data is of course not only used in Afghanistan, but is generally extremely valuable for large-scale analyses of snow. However, it is often difficult to determine whether the satellite really always sees what is actually happening on the ground. A large-scale citizen science project has been trying to remedy this situation for several years now and is calling on people to measure and report snow depths while on tour. (Wikstrom Jones et al, Community snow observations (CSO): A citizen science campagin to validate snow remote sensing products).

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We do not want to go into the following session contributions in detail here due to the high level of detail with relatively low relevance to skiing, but they should be mentioned here:

Measurement details

Fromm et al, A mechanical device determining the volumetric liquid water content of snow - snowpress.

Engel et al, How do different snowmelt sampling methods for tracers affect hydrograph separation? A comparative analysis in three alpine catchments.

Helfricht et al, Investigating performance and correlation of ground-based snow depth and precipitation measurements.

Modeling issues

Hirashima et al, Simulating Liquid Water infiltration - comparison between a three-dimensional water transport model and a dual-domain approach using snowpack.

Schellander et al, Bivariate spatial modeling of snow depth and snow water equivalent extremes in Austria. Winkler et al, Modeling SWE exclusively from daily snow depths.

Conclusion

The contributions to this session are somewhat mixed in terms of subject matter, but in summary it can be said that Climatic changes have an impact on snow and therefore also on the water balance. The warmer it gets, the higher the snow line rises, with corresponding consequences for the duration, height, composition, etc. of the snow cover. Accurate modeling of changes in the aforementioned parameters and relevant processes on a small spatial scale is difficult, although the large-scale trends are clear.

It is also still difficult to find out how much snow there is and how much water it contains. Attempts are being made to answer this question using various measurement methods and modeling approaches, but if you really want to know exactly, you should go skiing yourself and see if there is a nice dusting.