The water temperature is a key factor for the conditions in surface waters. It is one of the most important regulators of life processes in aquatic ecosystems. It influences all metabolic processes, the period, progression and rate of growth and the composition of biocoenoses. Preferences for and tolerances of specific temperature ranges restrict some species to certain sections of rivers. If the temperature limits for a given species are exceeded, the species will be unable to survive if it has no means of escaping to cooler waters.
The average temperature in the Rhine near Basel has risen by more than 2°C over the last 50 years. A similar change has been observed in other surface waters in the Central Plateau. Among the factors contributing to this development are climate change and the introduction of heated water (for example from cooling systems/plants or wastewater treatment plants). The ecological objectives for surface waters in the Water Protection Ordinance specify that the water quality should be maintained at temperatures which approximate to the natural conditions. The currently available data and information does not yet allow effects on biocoenoses to be specifically identified. For this reason, the state is assessed as neutral. However, due to climate change and the longer periods of warm temperatures, a further rise in the temperature of surface waters can be expected in the coming decades. The tolerance of sensitive aquatic organisms to additional temperature rises caused by human activity is then likely to decrease further. This creates an increased risk of disease.
The method is internationally harmonised. In the last century the water temperature in European rivers and lakes rose by 1-3 degrees as a result of atmospheric warming and also locally due to the discharge of heated water from cooling systems/plants and wastewater treatment plants (CSI of EEA: CLIM 019).
Europe is also observing a general rise in the temperature of surface waters (due to emissions and climate change). A direct comparison of the temperatures between regions/countries is not appropriate given the differences in natural landscape conditions (Alps and lowlands).
The FOEN has collected water temperature data since 1963 at a selected set of watercourse measuring points operated by the hydrometric network of the Confederation. Earlier data derive from measurements conducted by the International Commission for the Protection of the Rhine ICPR. In response to the development of temperatures since the late 1980s, the FOEN network was expanded substantially from 2001 onwards, to include measuring points on smaller bodies of water with a minimum of human interference. All the measurement sites are equipped with thermographs and data loggers. The latest data can be viewed on the internet or obtained as a text message on a mobile phone. The temperature data are published regularly in the Hydrological Yearbook.