In spring 2025, the water level of the Rhine was significantly below the long-term average. ‘Such conditions are a foretaste of what we can expect more frequently for the Rhine in spring and summer in the future,’ says ICPR President Miriam Haritz.
Low water levels are often accompanied by high water temperatures. The study published today uses model results to show a clear trend: the Rhine is warming significantly as a result of climate change.
Review: 45 years of proven temperature rise
The evaluation of historical measurement series for the period 1978-2023 has already shown a clear warming trend: the Rhine has warmed significantly since 1978, especially in the area south of Karlsruhe. For example, the average annual water temperature in Basel rose by 0.4 °C per decade during the study period. Although anthropogenic heat discharges – such as those from closed nuclear power plants – have declined, they have not been able to mitigate the rise in water temperatures, which is directly linked to the rise in air temperatures due to climate change.
Looking to the future: models up to the year 2100
The new simulations of water temperature development carried out as part of this study are based on the high CO2 emission scenario of the Intergovernmental Panel on Climate Change (IPCC). Experts from BfG, Deltares and the riparian states have carried out model calculations to quantify the expected rise in Rhine temperatures. They expect the Rhine water to warm by between +1.1 and +1.8 °C by the middle of the century. By 2100, the annual average water temperature could even rise by 2.9 to 4.2 °C compared to the period 1990-2010, which was used as a reference for all calculations. The study results show that the southern sections of the Rhine from Switzerland to Karlsruhe will be particularly affected.
Specifically, this means that, on average, the number of days with temperatures below 10 °C in the main stream of the Rhine will fall from the current 170 days to 104 days by the end of the century. Conversely, the number of days with temperatures above 21.5 °C will rise significantly, from the current average of 32 days to 106 days per year (corresponding to almost one third of the year). On these 106 days a year with temperatures above 21.5 °C, almost 50 days a year will see temperatures above 25 °C and up to 28 °C. The modelled water temperatures could also be exceeded due to factors not taken into account in the study, in particular anthropogenic heat discharges, which are difficult to predict.
Species and floodplains under pressure
Climate change is causing average air temperatures to rise, putting pressure on all natural habitats. Aquatic habitats and wetlands are particularly affected by climate change due to the increasing frequency and severity of low water levels and rising water temperatures, which worsen the effects of anthropogenic pressures from the various uses of the river and its habitats.
‘Rising water temperatures are having a significant impact on living conditions in the Rhine. If critical temperature thresholds are exceeded over long periods of time, ecological damage can occur. Aquatic organisms then suffer from heat stress, for example, which weakens them and makes them more vulnerable to disease,’ says Tanja Bergfeld-Wiedemann, a BfG scientist who collaborated on the study. ‘At higher temperatures, the solubility of gases in water also decreases, which means that less oxygen is available to the animals,’ claims the biologist.
The heating of the water in winter also provides favourable conditions for the spread of certain invasive alien species. In the long term, species such as the grayling, which prefers cold water, could suffer population declines or disappear from parts of their current range in the Rhine system. Predatory fish that are not sensitive to temperature, such as catfish, are strengthened and exert additional pressure on aquatic species, although some of them die at temperatures around 25 °C.
The rise in water temperature can be limited in small tributaries by creating shaded refuges, restoring riparian forests and restoring healthy floodplain ecosystems. In large tributaries and in the main channel of the Rhine, measures are more difficult to implement..
Restrictions on water use threaten
If the water temperature rises above a threshold value, the competent authorities may be forced to impose restrictions on water use (e.g. industrial or agricultural withdrawals), which can lead to conflicts over use and economic difficulties. The rise in temperature will result in less capacity being available for existing and new cooling water consumers.
It is therefore essential to intensify the work already underway in the countries in order to strive for economical and sensible water use in consultation with the users who depend on this shared resource.
Modelling across national borders
The study was the first to test a cross-border model approach that combines national model results from Switzerland, Germany and the Netherlands along a uniform climate signal. ‘Close cross-border cooperation was crucial to obtaining a consistent picture of future water temperatures along the entire Rhine,’ says Pascal Boderie, research scientist at Deltares.
Adaptation as a shared responsibility
As part of the ongoing update of their strategy for adapting to climate change, the countries in the Rhine catchment area are working under the umbrella of the ICPR on concrete measures that take into account the various uses of the river. The aim is to preserve and strengthen the ecological functions of the Rhine. The results of the temperature analyses are fed directly into this process.
Further information:
- Simulation of the effects of climate change scenarios on future Rhine water temperature development – update IPCC AR5 –
- Development of Rhine water temperatures from 1978 to 2023 (available in German, French and Dutch)
Press contact ICPR: Marc Daniel Heintz, Tel. 0049-261-92525-19, E-Mail: marcdaniel.heintz@iksr.de
Press contact BfG: Dominik Rösch, Tel.: 0261/1306 5000, E-Mail: presse@bafg.de
Press contact Deltares: Pascal Boderie
In the International Commission for the Protection of the Rhine (ICPR), Switzerland, France, Germany, the Netherlands, Luxembourg and the European Union have been working together for mor than 70 years on the basis of a convention under international law to reconcile the diverse uses and protection of water bodies. With a view to implementing European directives, the cross-border cooperation was extended to Austria, Liechtenstein, Italy and the Belgian region Wallonia. At present (2023-2025), Miriam Haritz from Germany holds the ICPR presidency. She and the different ICPR groups are supported by the international staff of the permanent secretariat in Koblenz (Germany).
The Federal Institute of Hydrology (BfG) is a federal authority within the remit of the Federal Ministry of Transport (BMV). It is the federal scientific institute for water-related research, assessment and consulting, particularly in the fields of hydrology, water use, water quality, ecology and water protection. The work of the BfG primarily covers navigable rivers, canals and coastal waters (federal waterways) administered by the Federal Waterways and Shipping Administration (WSV). As a departmental research institution, the BfG is part of the German scientific landscape.
As a knowledge institute, Deltares has been providing reliable expertise in the field of water and the subsurface for over a century. The unique combination of knowledge and research, experts, experimental facilities, key technologies, specialised software and data products enables us to advise policymakers and industry and to tackle current challenges.