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

What's happening in snow science?

by Lea Hartl 01/23/2020
Every two years, the International Snow Science Workshop (ISSW) brings together scientists and practitioners from a wide range of different, but always snow-related, subject areas. New findings and research results are presented in various thematic blocks - so-called sessions. We break the whole thing down into more or less digestible morsels and summarize the sessions of the ISSW2018 for you every two weeks.

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)

Different countries and mountains, similar trends

Studies from different regions look at observed (already happened) and modeled (will happen in the future) changes in snow cover due to climate change. A model-based study from Japan, for example, expects significant decreases in the amount of new snow, maximum and average snow depths and days with snow cover on Hokkaido, with different climate models providing different results in detail (Katsuyama et al., Global warming response of snowpack in Hokkaido, Northern Island of Japan).

In the Italian Alps, a decrease in the amount of new snow and snow cover can be observed, particularly in spring. In March and April, there is less and less snow, especially in the altitude range between 800-1500m, and the altitude line from which snow can be reliably expected (from December to April at least 100 days with at least 30cm of snow cover - typical parameter) has risen by up to 300m (Valt et al., Snow cover and climate changes in the Italian Alps (1930-2018)). Measurement data from other Alpine regions show a similar picture.

A study from Russia attempts to determine trends in the number of "extreme" snowfalls and finds that there is too little data on this topic and that - based on the not particularly good data basis - heavy snowfalls tend to occur more frequently, which cause problems for traffic and infrastructure. Unfortunately, it is rather rare for Russian work of this kind in English to make it into the international research landscape. The language barriers are also evident in this case at the latest in the Cyrillic axis labeling of the figures ( Fedotava, Extreme snowfalls in Russia).

The leap in scale from the global mean temperature increase to concrete effects on the snowpack at the local level is anything but trivial and there are still various challenges for the modelers here. Using the Chartreuse massif near Grenoble as an example, an attempt was made in this direction and a climate model was coupled with a snow cover model (Crocus). For a global temperature increase of 1.5°C, a snow cover decrease of 25% is projected at approx. 1500M (Chartreuse) - for stronger temperature increases correspondingly more (Morin et al., Linking Variations of meteorological and snow conditions in the french mountain regions to global temperature levels).

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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Miscellaneous - not uninteresting, but missing the point of the session?

Avalanches sometimes contribute significantly to winter accumulation on glaciers, which in turn has an impact on the hydrological conditions in the catchment area (Lazarev et al, Estimation of accumulation from snow avalanches in the mountain glaciers).

A sliding snow avalanche threatening a road in Norway has been observed and measured using various methods for several years. InSAR (radar interferometry) monitoring appears to be the most practical and best suited for an operational warning system (Humstad et al, The Stavbrekka glide avalanche in Norway - lessons learned after three years of monitoring).

In the Kunes Valley in Tianshan, China, there were five significant avalanche events associated with earthquakes in the period 2011-2017. (Hao et al., Climatic factors triggering snow avalanche in Kunes Valley of Tianshan Mountains, China (no ext. Abs)).

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.

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This article has been automatically translated by DeepL with subsequent editing. If you notice any spelling or grammatical errors or if the translation has lost its meaning, please write an e-mail to the editors.

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