Snow as a water resource

The topography of Switzerland is highly mountainous. A good 50% of its surface is above 1000m and almost 25% is above 2000m. Therefore, a third of the total precipitation happens as snow.

Fig. 1: Water reservoir in the Swiss Alps.

A large proportion of the rainfall is first stored as snow which then melts into the soil or evaporates into the atmosphere. Depending on altitude and weather, snow either melts directly on a warm ground, after a few months at the end of winter, or even after decades from a glacier.

Influence of climate change on snow and hydropower

Hydroelectricity is very important for Switzerland and many power stations are fed by alpine catchments. These catchments are characterized by very uneven snow distributions (both daily and yearly) which cause highly variable stream flows towards the reservoirs. This is a challenge for the power stations operators who know the specificities of their regions from years of experience. Historical knowledge is however insufficient to predict the effects of climate change. Our research effort is therefore directed towards predicting these effects. We have, for example, modelled snow accumulation today and in 100 years in an alpine catchment feeding a water reservoir in the canton of Uri.

Fig. 2: Results of snow depth modeling in our study site, today and in 100 years. Left: percentage of snow-covered areas (SCA) during the year. Right: total quantity of water stored in snow cover during the year (SWE).

We accounted for the evolution in temperature and precipitation as predicted by regional climate change models. Model results show that the current snow conditions will shift upwards by about 500 meters over the next 100 years. The amount of water stored in the snow cover will drastically decrease (Fig. 2, right), while the duration of winter snow cover will be shortened by at least 2 months (Fig. 2, left). The reduced importance of snow as temporary storage for rainfall may increase the probability of extreme hydrological events.

Snowmelt-related flood risk

In spring, flood situations can occur if large amounts of snow suddenly melt because of warm temperatures combined with heavy rain. We therefore study the formation and drainage of snowmelt with the help of snow hydrological models and data from the catchment. This analysis supports the services in charge of flood prevention. For example, in winter we regularly supply snow hydrology reports to the federal office for the environment (FOEN).

Fig. 3: Snowmelt is the cause of high stream levels in the spring.

Snow hydrology measurement and modeling

A key research objective is to estimate how much snow there is in alpine basins and what proportion of it flows out as snowmelt. For this purpose, we generally use a combination of field measurements and snow hydrological models. To improve existing analytical and forecasting models, we are working on the optimization of many components. A good location for the stations and optimal measurement techniques play an important role in the acquisition of reliable field data. Also, studying the relevant physical processes is needed to improve their representation in the model. Finally, the quality of the modeling results is estimated against the corresponding field measurements (e.g., the snow distribution in the catchment area). You can find a list of our current snow hydrology project here.