In order to be able to describe the climate of a region, meteorological parameters such as temperature, precipitation and sunshine duration are analysed over defined periods of 30 years according to the specifications of the World Meteorological Organisation (WMO). The mean values of these periods are known as climate normals. The 30-year period itself is referred to as a normal or reference period.
The normals enable the climates of different locations to be compared with one another. Furthermore, they allow current weather situations to be evaluated in context. By comparing current observation values with the climate normals, we can draw conclusions about whether the observed period was warmer, drier or sunnier than the expected climate.
The normal periods are updated every ten years. This ensures that they appropriately describe the current climate of a region despite ongoing climate change. Since January 2022, the most recent normal period of 1991–2020 has been used.
In accordance with WMO recommendations, 1961–1990 is used as the reference period for observing long-term climate development. The pre-industrial reference period, which for Switzerland is 1871–1900, is used to determine the influence of humans on the global climate.