Measuring snow in Davos—day by day, year by year

At the Weissfluhjoch test site near Davos, the WSL Institute for Snow and Avalanche Research (SLF) has been measuring the snowpack daily since autumn 1936. Collected by the "Jochdienst" using traditional methods and state-of-the-art measurement technology, this unique long-term snow data series provides vital information for climate research, avalanche warnings and flood forecasts.

December in the Parsenn ski resort near Davos. In glorious sunshine, a group of skiers zigzag their way down the slope towards the middle station. Nothing unusual in that, you might think. But all of a sudden the group leaves the piste and heads off into open country. After a few meters, they reach the SLF's Weissfluhjoch test site.

Researchers have been collecting snow data here since autumn 1936, including the structure of the snowpack, its water content and depth. In winter, this is done every day, early in the morning, whatever the weather, and in summer whenever there is snow on the ground—a total of eight months a year.

The resulting decades-long measurement series at this elevation is unique. As well as being available to snow researchers from around the globe, the data is used at the SLF in numerous projects, ranging from climate research to snow climatology, flood forecasting to avalanche warnings.

The team responsible is known as the "Jochdienst" (Joch service). It is made up of 20 to 25 SLF doctoral students, who work in weekly shifts. On this December day, they are being given their annual induction.

Sensitivity and a good eye

Some methods were already being used by scientists in the first half of the 20th century. This ensures that data can be compared and trends identified without having to recalculate old results. Other techniques and equipment have been added over time, such as the SnowMicroPen (SMP), developed in-house at the SLF.

"This allows us to find out details about the layers in the snowpack," explains SLF technical staff member Matthias Jaggi. "Please handle it carefully." Repairing the SMP could easily cost several thousand Swiss francs. Today, everyone is allowed to try out the device once away from the test site.

Sensitivity is the order of the day here, whereas measuring the depth of the snowpack requires a good eye. From several meters away, the doctoral students take a reading from markings on a pole in the snow. Next step: what does the top layer of snow look like? "Today we have surface hoar on a crust several centimeters thick," says avalanche warning officer Jürg Trachsel. Observing and reporting surface hoar is very important for avalanche warnings. "As soon as the hoar gets covered in snow, it becomes a weak layer in which avalanches can easily be triggered," he explains.

Snow on the scales

Trachsel was himself a member of the Jochdienst during his time as a doctoral student at the SLF. "Back then, we stayed overnight in the former institute building on the Weissfluhjoch. It was really cool, seeing the sun rise early in the morning when no one else was up yet," he recalls. But those days are over.

For years now, Jochdienst members have made their way up from the valley each day. In winter, they can take the train used by the mountain railway staff, before the tourists are up and about. In the off-season, they walk up, use snowshoes or touring skis or ride the institute's e-bike. "But the bike isn't suitable for all weather conditions. I got stuck in the mud while riding downhill and had to carry it down the mountain," says Julia Miller, who is already in her third season of Jochdienst and is refreshing her skills.

After that, it's time for the team members to unleash their inner child. SLF researcher Julia Glaus demonstrates how the Jochdienst cuts out fresh snow using a large, round mold. She takes it to a small hut next to the test site and places it on weighing scales. The researchers calculate the snow water equivalent (SWE) based on the mass.

The hut also houses the computer in which the doctoral students enter their measurements. These are then immediately available to all scientists on the SLF computer network and, in some cases, to the public. It is now late morning. The doctoral students have completed their training—time to head back down to the office.

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 millimeters. Each millimeter corresponds to 1 liter of water per square meter of snowpack. One centimeter of fresh snow with a typical density of 100 kilograms per cubic meter results in 1 millimeter of water. An example: in mid-April 2024, the average density of the snowpack at the Weissfluhjoch test site was 416 kilograms per cubic meter, which for a snow depth of 2.7 meters corresponds to a water equivalent of around 1,100 millimeters or 1,100 liters of water per square meter.

Provided by WSL Institute for Snow and Avalanche Research SLF