Water temperature is one of the key physical parameters that determines chemical and biological processes in a watercourse. The FOEN’s measurements are the basis for monitoring temperature changes and understanding their causes.
A clear trend toward warmer temperatures can be seen when looking at long-term changes in water temperatures in Swiss bodies of water. In the section of the Rhine River at Basel, the temperature has risen by more than 2°C since the 1960s. Similar temperature increases can also be observed in other bodies of water in the Central Plateau. Climate change and heated water discharged from sources such as cooling systems (e.g. for nuclear power plants or industry) or even wastewater treatment installations are contributing to these changes.
Water temperature is a key factor in the state of surface water. All metabolic processes, growth and composition of biotic communities are influenced by it. The viability and activity of aquatic organisms are dependent on certain temperature limits and optima. That is why knowledge of temperature dynamics is an extremely valuable interpretative tool.
Due to climate change, the temperature of surface waters is expected to rise further in the coming decades. This will put more pressure on sensitive aquatic organisms in specific stretches of watercourses and progressively destroy the conditions they require for survival. These changes will also increase the risk of diseases in aquatic organisms. The FOEN is currently conducting a preliminary study on the problem of rising temperatures in the context of climate change and anthropogenic influences. The findings of this study will be used to identify the priority areas where action needs to be taken. Less tolerance may need to be shown to the additional heat discharged by human activities.
In accordance with the ecological goals of the Waters Protection Ordinance, the temperature conditions of surface waters must be as near natural as possible.
The FOEN's temperature monitoring network provides the bases for enforcing the water protection legislation and makes it possible to analyse the causes. In cooperation with cantonal and national agencies and research institutes, the FOEN is studying the impacts on organisms such as fish.
Current temperature data from around 80 gauging stations along watercourses throughout Switzerland can be consulted on the Internet or received by SMS on mobile telephones. Temperature data evaluations are also published in the Hydrological Yearbook of Switzerland.
The water temperatures of few Swiss lakes are being recorded by the federal government as part of a pilot project.
