• Measuring snow: At the SLF’s Weissfluhjoch test site, climate researcher Christoph Marty collects basic data on the structure, depth and water equivalent of the snowpack.
• Water issues in the context of climate change: The data is fed into models that show how snow and evaporation are changing, with implications for electricity generation, agriculture and water supply.
• Unique measurement series stretching back to 1936: The test site provides the world’s longest series of daily snow measurements at high altitude – an indispensable basis for snow, water and climate research.

“The weather forecast was fifty-fifty, sun or overcast. At any rate, we have powder snow,” says Christoph Marty, making his way down the piste. It is just before half past eight on a Thursday morning in March. Snow is falling and visibility is just a few metres. Marty is on his way to the Weissfluhjoch test site belonging to the WSL Institute for Snow and Avalanche Research (SLF), around 150 metres below the Parsenn Funicular's mountain station.
Marty is a snow climatologist at the SLF and an expert on the long-term development of snow depths. At the test site, he regularly collects data that is important for his own work and that of his colleagues.
Today, he is accompanied by master’s student Isabella Anglin and intern Leah Gaillard Festa. The three get down to work, starting with shovelling. To collect the data, Marty needs a hole measuring several square metres and extending down to the ground. “We’re lucky, today the snow depth is only 127 centimetres; it could be 3 metres,” he says. Marty is up here digging multiple times each winter. He has no idea how many tonnes of snow he has shifted in the course of his career, but it’s a lot.
He also measures the temperature of the snow. The thermometer shows minus 2.6 degrees Celsius. “That means the snowpack isn’t wet yet,” explains the scientist. Next, he unpacks the ram penetrometer, a broad metal rod at the end of which a weight is mounted on another, thinner rod. In a technique akin to some egg toppers, he repeatedly drops this weight onto the upper end of the bar. This enables him to determine how hard individual snow layers are. “Ten times five, 52,” he calls out to Gaillard Festa, who notes down the figures. “Four times five, 75.”
Marty then drives a metal cylinder into the snowpack from above until it is filled with a column of snow. He hangs this on a spring balance, which enables him to work out the density of the snowpack. This information combined with the snow depth can be used to determine the water equivalent of the snowpack – another key indicator.
“It’s so clever the way you measure here,” says Gaillard Festa. Today is her first time helping out. In the future, she will also be taking measurements herself. “Well, we’ve had around 90 years to develop and hone our techniques,” replies Marty. Such long time series are valuable in climatology, with researchers always using the same methods, some of which go back a long way. This makes it easier to compare the data.
Located at an altitude of 2,536 metres, the test site was set up in 1936 by the Weissfluhjoch research station run by the Swiss Snow and Avalanche Research Commission, the forerunner of the SLF. Originally intended for snow and avalanche research, the data was later also used by the avalanche warning service. Today, it also provides important insights into the effects of climate change.
Since the test site was established, researchers have carried out countless experiments here on snow mechanics, snow metamorphism, snow characterisation and measuring methodology. Data has been collected daily ever since, whenever there is snow on the ground. It is the world’s longest continuous series of daily measurements in this altitude zone. PhD students at the SLF take turns working in shifts, with one person coming up to the site every morning to record basic data.
In science, it is often important to use time-honoured techniques, as is the case here, even if they date back to the 1930s. This is because reliable data sets are needed to develop high-tech methods and equipment. The painstaking manual work provides an important benchmark for modern measuring devices. Indeed, a range of devices such as laser scanners, ultrasonic sensors, radars and many more can be found at the site, suspended from numerous poles. Private-sector companies also make use of the SLF’s expertise. They are continually installing new sensors at the test site and comparing the data from their instruments with the SLF’s figures.
Long-term data series that are always collected using the same methods are also vital for research, especially in an era of climate change, as people such as Christoph Marty can use experiences from the past to make predictions for the future. He gives an example: “If we see a trend towards less snow as a result of climate change, that also means that we’ll have less water available in a dry summer in Switzerland.” This affects energy suppliers and agriculture as well as anglers and garden owners. The institute’s high-tech equipment also supplements the hand-collected data series with key information that leads to even better results.
Meanwhile, master’s student Anglin is busy taking numerous snow samples and putting them in plastic tubes. She will send these to ETH Zurich, where the samples are placed in a mass spectrometer. Anglin is investigating the ratio of water molecules with oxygen and hydrogen atoms of different weights, known as isotopes. She aims to use this information to determine the extent to which snow evaporates, with a view to enhancing the models. “Depending on the weather conditions, evaporation can make up an important part of the water balance. We want to quantify this,” explains the chemical engineer.
By now, the sun has come out. Marty straps on his skis and makes his way back down the valley to his desk, where he will process the measured data. This is not only for his own research. Other groups at the SLF, such as the operational snow-hydrological service (OSHD), as well as the Federal Office for the Environment also benefit from such measurements because they can be used to improve runoff forecast models.
Anglin and Gaillard Festa stay up at the test site. They have more samples to take, and will then have to fill the hole back in.

What is... snow water equivalent (SWE)?

A snowpack consists of numerous layers of more or less compressed (dense) snow. The snow water equivalent indicates how high a layer of water would be after the snowpack has melted, expressed in millimetres. Each millimetre corresponds to one litre of water per square metre of snowpack. One centimetre of fresh snow with a typical density of one hundred kilograms per cubic metre results in one millimetre of water. An example: in mid-April 2024, the average density of the snowpack at the Weissfluhjoch test site was 416 kilograms per cubic metre, which for a snow depth of 2.7 metres corresponds to a water equivalent of around 1,100 millimetres or 1,100 litres of water per square metre.

This article first appeared in an abridged version in the Davoser Zeitung on 29 April 2025.