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Long-term data series for temperature, precipitation and sunshine duration are available at MeteoSwiss. For several locations, these date back as far as 1864 (Swiss National Basic Climatological Network). These long-term data series are extremely valuable for understanding climate change both in the past and the present. To ensure that man-made changes such as station relocations or the use of new measuring instruments do not have a confounding influence on the results, the measurement data are extensively checked for measurement errors and temporal homogeneity before being analysed.
(homogenisation).
Statistical methods can be used to derive values from the measurements at the individual stations for any location in Switzerland where there is no measuring station. This makes it possible to create maps displaying the changes in temperature, precipitation and sunshine duration for the whole of Switzerland. In addition, they can be used to calculate mean values for individual areas.
Clear signs of warming in the country as a whole
The annual mean temperature has risen by around 2°C (linear trend) in Switzerland since 1864. This is equivalent to an increase of between 0.08 and 0.15°C per decade. The increase was somewhat greater north of the Alps than in the south. Aside from this, the annual mean values show no major geographical differences in the warming trend. The trend towards warmer temperatures is statistically significant in all parts of the country. According to current global climate research, it is clear that this trend can only be explained in terms of the human contribution to the increase in global greenhouse gas concentrations.
Differing extent of warming depending on the time of year
When the individual seasons are looked at separately, significant regional differences can be seen in terms of warming trends. While the lowlands of central Switzerland saw a steeper rise in temperatures than the mountainous regions in winter, the opposite scenario was true for the summer months. In spring and autumn, all regions warmed to the same extent, with a greater increase in autumn temperatures than in spring in most regions. The warming trends are also statistically significant across the whole of Switzerland when looked at for each season.
In autumn and winter, temperature change has been very consistent since measurements began:
- Between 1880 and 1890, winter temperatures were at an extremely low level, while autumn temperatures were likewise exceptionally low between 1880 and 1920.
- In winter, the period from 1900 to 1980 was uneventful, with no clear trend observable, which was also the case in the autumn months during the period from 1920 to 1980.
- In 1987 and 1988, there was a sudden shift to a pronounced period of warm winters, although this trend has been somewhat muted over the past 15 years with a few cooler winters.
- Very low autumn and winter temperatures have not been seen since the end of the 20th century.
Spring and summer temperature trends were very similar:
- The 1940s were warmer than average.
- Temperatures held steady between 1960 and 1980.
- During the course of the 1980s, temperatures rose markedly and have since remained at a high level.
Mean winter precipitation is increasing in some regions
Warming has resulted in heavy precipitation becoming a more frequent occurrence throughout Switzerland. However, in terms of annual precipitation amounts since measurements began in 1864, a statistically significant increase is only observed over the northeastern Swiss plateau. This is mainly due to higher amounts of precipitation in winter. The fact that no significant changes in precipitation have been observed in the other regions cannot be conclusively explained at present. Changes in the frequency of weather situations are probably an important factor.
Different regional patterns can be identified in the long-term data series of precipitation measurements. This is primarily due to the influence of the Alps, which act as a climatic barrier. As a result, a northern Alpine and a southern Alpine precipitation pattern are found in Switzerland. When precipitation changes are shown for the whole of Switzerland, significant regional differences are obscured.
The following notable changes in precipitation can be seen:
- After a phase in which springtime had considerable levels of precipitation in the south between 1975 and 1990, spring has been significantly drier since then in that region.
- In the north of the Alps, spring has become rainier in recent years.
- In winter, the precipitation amount has decreased significantly at many weather stations, especially in the Alpine region and in the west of Switzerland.
Sunshine duration has been on the increase since 1980
For sunshine duration, MeteoSwiss only has data series stretching back to the 19th century for a few weather stations at the moment. These stations show a substantial decline in sunshine duration from around 1960 to 1980. After that, the values rose again to their original levels. Some of the sunniest years occurred after 2000. This development is less pronounced in higher-altitude areas, especially at summit locations.
The graphics shown on the development of temperature, precipitation and sunshine duration draw on data from measuring stations of the Swiss Climate Network, which consists of 29 climate stations and 46 precipitation stations. In order to obtain an average for the whole of Switzerland or defined sub-regions for temperature and precipitation, the measurement data from the individual stations is combined and weighted according to their level of representativeness. The methodology applied for determining the weightings is published separately.