Since the beginning of the 20th century, the zero-degree line in Switzerland has risen sharply in winter. At high altitudes, precipitation increasingly falls as rain rather than snow. As a result, snow cover is gradually retreating into the higher elevations of the Alps. This trend will continue to intensify in future. The rise in temperatures is also responsible for a decline in the number of frost days.
Focus
- Around 1900, the winter zero-degree line was still at the average elevation of Zurich, about 420 meters above sea level. In the reference period 1991–2020, it had already risen to the elevation of Einsiedeln, 900 m a.s.l. With global warming of 3 °C compared to pre-industrial times, the zero-degree line will rise by a further 550 metres.
- In future, average snow cover in winter will decrease significantly, especially at medium altitudes between 1000 m and 1500 m, by around 78 % compared to the reference period 1991–2020, if global warming reaches 3 °C.
- With global warming of 3 °C, the average number of snowfall days per year at elevations between 1000 and 1800 m a.s.l. will decrease by about 45 % compared to the reference period 1991–2020. The average number of frost days per year will also decrease – in Davos by around 20 % compared to the reference period 1991–2020.
Snow is not only important for winter tourism, but also for sectors such as water management, hydropower, spatial planning, management of natural hazards and transport. Cold days are an important prerequisite for the formation of snow cover in winter sport areas. Furthermore, frost poses a risk to agriculture and can also lead to increased traffic accidents.
Further information on the effects of climate change and mitigation measures taken in various sectors can be found on the website of the National Centre for Climate Services (NCCS).
Observed decline in snow and cold temperatures
Rising temperatures have visibly changed the winter landscape in Switzerland over the past century. Precipitation in the form of snow has decreased in Switzerland. The resulting decline in winter snow cover is particularly pronounced at low and medium altitudes.
Since the 1960s, there has been a clear decrease in the number of days with fresh snow as well as in the fresh snow depth in many areas. The result is that total snow cover is less frequently recorded at many weather stations nowadays than it was during the period from 1960 to 1985. The decline is even noticeable at higher altitudes in the Alps. Winter sports resorts at medium altitudes, for example in the Alpine foothills, are particularly affected by this change. The example of Elm shows how the number of days with at least 1 cm of snow is decreasing. Reduced snowfall also enhances the melting of glaciers by losing the protective surface layer and preventing vital recharge in Winter, to the glacial system.
Due to climate change, there are fewer and fewer frost days throughout Switzerland. Less cold weather also means less need for heating, as the number of days per year for which heating is normally required, is declining.
Observed rise in the zero-degree line
In winter, the zero-degree line is lower and in summer it is higher. Due to global warming, the zero-degree line near the ground has risen by several hundred metres over the last 150 years. Around 1900, the winter zero-degree line was still at the average elevation of Zurich, about 420 meters above sea level. In the reference period 1991–2020, it had already risen to the evelation of Einsiedeln, 900 m a.s.l.
What exactly is the zero-degree line?
The zero-degree line marks the evelation at which the air temperature is exactly 0 °C. It separates warmer layers of air below, from colder layers of air above and thus often determines whether precipitation falls as rain, or as snow. A basic distinction is made between the zero-degree line near the ground and the zero-degree line in the free atmosphere, as recorded by a radiosonde.
A Look into the Future
Zero-degree line in the future
With global warming of 1,5 °C compared to the pre-industrial reference period – in a so-called 1,5-degree world (GWL1.5) – the zero-degree line will rise by a further 200 metres, slightly above the elevation of Gstaad (1,050 m a.s.l.). A 1,5-degree world is imminent. In a 3-degree world (GWL3.0), it will rise by a further 550 metres, reaching approximately the elevation of Andermatt (1,450 m a.s.l.). The zero-degree line will also rise significantly in summer, accelerating the melting of snow and ice even on the highest Alpine peaks.
In future, snow will melt much earlier in all locations, reducing the capacity of snow cover to store water. Consequently, meltwater will increase in the winter half-year but decrease in the summer half-year, leading to lower river discharge in summer.
Decline in snow cover
In future, less precipitation falling in the form of snow is expected in winter. In a 3-degree world, the snow share will drop by around 25 %, while rainfall will almost double. As a result, snowfall amounts will decline markedly despite higher overall precipitation. This will have a significant impact on winter snow cover, as shown by the snow water equivalent (water stored in the snow cover):
- In a 1,5-degree world, the snow cover at altitudes of 500 to 1000 metres will decrease by around 57 %, compared to the reference period 1991–2020. At elevations of 1,000 to 1,500 metres and 1,500 to 2,000 metres, a decline of around 51 % and 34 % respectively, is expected.
- In a 3-degree world, snow cover at altitudes of 500 to 1,000 metres will decrease by about 80 %. At altitudes of 1,000 to 1,500 metres and 1,500 to 2,000 metres, a decrease of about 78 % and 63 % respectively is expected.
| 1.5-degree world | 3-degree world | |
|---|---|---|
| 2000 to 2500 m | -19 % (-39 to 0 %) | -44 % (-57 to -28 %) |
| 1500 to 2000 m | -34 % (-63 to -19 %) | -63 % (-82 to -47 %) |
| 1000 to 1500 m | -51 % (-76 to -29 %) | -78 % (-92 to -65 %) |
| 500 to 1000 m | -57 % (-81 to -36 %) | -80 % (-92 to -71 %) |
Relative change (%) in snow water equivalent (water stored in the snowpack) compared to the reference period 1991–2020. Swiss average between September and May depending on the evelation. Shown are the expected values and the possible ranges of change.
Fewer snowfall days
The more the climate continues to warm in future, the more pronounced the decline in snowfall days will be:
- In a 1,5-degree world, around 3 to 4 fewer days of fresh snowfall per year are expected for the Swiss Plateau. At altitudes between 1,000 and 1,800 metres, around 10 days fewer, or 23 % fewer, are expected compared to the reference period 1991–2020.
- In a 3-degree world, around 6 to 11 fewer days of fresh snowfall are expected for the Swiss Plateau, which corresponds to roughly half of the previous number of days of fresh snowfall. At altitudes between 1,000 and 1,800 metres, around 20 fewer days, or 45 %, are expected.
Further decline in cold days
In addition to changes in snow and the zero-degree line, a noticeable change is also expected in the number of frost days and ice days. With the rising zero-degree line, the probability of frost at lower and medium altitudes will decrease significantly. This can be clearly demonstrated using the Davos measuring station as an example:
- During the WMO reference period (1961–1990), an average of 210 frost days were recorded at the Davos measuring station. In the current reference period (1991–2020), the average is only 187.
- In a 1,5-degree world, the average number of frost days at the Davos measuring station is expected to fall to 174 days.
- In a 3-degree world, the number of frost days at the Davos measuring station is expected to decrease to an average of 149 days.
It is therefore expected, in a world that is 3 °C warmer, the Davos measuring station will see a further reduction of around 20 % in the number of frost days, compared with the current reference period (1991–2020).
