Early warning tool for river fish in heatwaves
en-GBde-DEes-ESfr-FR

Early warning tool for river fish in heatwaves


Researchers from the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) propose a warning tool which predicts, up to three weeks in advance, when river fish in Switzerland are at risk from heat. As heatwaves become more frequent with climate change, this early warning system gives the time to act and protect fish populations from future heatwaves.
  • A forecasting tool warns when river fish are at risk from heat stress in Switzerland.
  • The system estimates future risk using water temperature predictions and the heat sensitivity of local fish populations.
  • The forecasts are openly accessible online to help manage river ecosystems proactively and protect fish populations.

Preparing for weather extremes

When do rivers become too hot for river fish in Switzerland? To predict when river fish are at risk from heatwaves, ecologists and climatologists at the Swiss Federal Institute for Forest, Snow and Landscape Research WSL joined forces with experts from across Switzerland to develop a forecasting tool, published in the Journal of Ecological Modelling. The forecasts are updated twice a week and publicly available on drought.ch.

With heatwaves becoming more frequent and severe due to climate change, fish are particularly at risk, as their body temperature depends entirely on their environment. Unable to cool themselves down, fish are ectothermic, more commonly referred to as “cold-blooded” animals. “When the water temperature rises, chemical reactions in the fish’s cells change — and that’s what we call heat stress”, defines Camille Albouy, senior researcher at the joint WSL and ETH research group Ecosystems and Landscape Evolution.

From past data to future risk

The new tool predicts, up to three weeks in advance, how at-risk fish populations are from heat across Switzerland. The predictions are based on three parameters: water temperature forecasts, fish physiology and species distribution. WSL’s hydrological forecasting group developed the water temperature forecasts. “Our machine-learning model, trained on data from the past 10 years, uses the latest water temperature observations and weather forecasts to predict river temperatures”, explains Ryan Padrón Flasher, one of the group’s members.

Not all fish are equally sensitive to heat. Searching through published data, the authors gathered information on the temperature limits of 59 fish species found in Swiss rivers. This is the temperature at which their ability to swim, and therefore to escape from dangerous conditions, is impaired. The authors found non-native fish species to have a temperature tolerance 1.4°C higher than native species on average. The bighead carp (Hypophthalmichthys nobilis) held the highest tolerance of 32.3°C, while the burbot (Lota lota) was the least tolerant, with 24.1°C.

Finally, as fish species are unevenly present across Switzerland, including information on their distribution makes the forecasts location specific. “It’s a constant compromise between the complexity and quality of the model”, explains Camille Albouy. “As the idea was to develop a map of risk for the whole of Switzerland, based on the best climate predictions, we had to keep it simple and focus on what matters for management.”

With the help of hindsight

To evaluate the forecasts, the scientists applied their tool on data from summer 2018, when around three tonnes of river fish died in Switzerland. “We wanted to see how well we could retrospectively predict the observed fish mortality”, says Camille Albouy. However, this proved more challenging than expected. “Data on fish mortality are limited,” he clarifies, “so we reached out to practitioners to see if their observations matched our predictions.”

Out of the three reported cases of fish mortality in 2018, the tool predicted two correctly. Across the remaining locations, forecasts were 70% accurate, successfully identifying areas of low and moderate risk. However, at five sites the tool overestimated the level of risk, likely because it does not include finer-scale information like local population sizes or the presence of cooler refuges within rivers. “It’s a promising start” says Camille Albouy, “now we need to see if it grows into a long-term solution for Swiss rivers.”

Bonaglia, A., Shen, C., Padrón, R. S., Bogner, K., Fopp, F., Rubin, A., … Pellissier, L. (2025). Sub-seasonal forecasting of thermal stress for Swiss river fishes during heatwaves. Ecological Modelling, 507, 111171 (14 pp.). https://doi.org/10.1016/j.ecolmodel.2025.111171
Angehängte Dokumente
  • Trota atlantica Salmo trutta, highly heat-sensitive (photo: Ulrich Wasem)
  • Cavedano Squalius cephalus, low sensitivity to heat (photo: Ulrich Wasem)
  • Shade from foliage and deadwood creates locally cooler environments (Foto: Ulrich Wasem).
  • Barbo Barbus barbus moderately heat-sensitive (photo: Ulrich Wasem)
Regions: Europe, Switzerland
Keywords: Science, Environment - science

Disclaimer: AlphaGalileo is not responsible for the accuracy of content posted to AlphaGalileo by contributing institutions or for the use of any information through the AlphaGalileo system.

Referenzen

We have used AlphaGalileo since its foundation but frankly we need it more than ever now to ensure our research news is heard across Europe, Asia and North America. As one of the UK’s leading research universities we want to continue to work with other outstanding researchers in Europe. AlphaGalileo helps us to continue to bring our research story to them and the rest of the world.
Peter Dunn, Director of Press and Media Relations at the University of Warwick
AlphaGalileo has helped us more than double our reach at SciDev.Net. The service has enabled our journalists around the world to reach the mainstream media with articles about the impact of science on people in low- and middle-income countries, leading to big increases in the number of SciDev.Net articles that have been republished.
Ben Deighton, SciDevNet
AlphaGalileo is a great source of global research news. I use it regularly.
Robert Lee Hotz, LA Times

Wir arbeiten eng zusammen mit...


  • The Research Council of Norway
  • SciDevNet
  • Swiss National Science Foundation
  • iesResearch
Copyright 2026 by DNN Corp Terms Of Use Privacy Statement