1. Chief Scientist’s Group report summary

This project developed water temperature projections to the year 2080 for English rivers. Knowing how rivers will warm will help the Environment Agency and others consider the potential impacts of climate change and inform where adaptation measures may be needed.

1.1 Background

Climate change is anticipated to increase water temperatures in English rivers. These changes will affect water quality and the health of river ecosystems. This includes impacts on important salmonid fish species such as Atlantic salmon and brown trout.

1.2 Approach

Observations of river temperature collected over many years were used to develop models of monthly mean daytime temperature. The models include variables about the stream network and site geography as well as air temperature. Including air temperature meant the models could use climate change projections for future UK air temperature (using a high emission scenario) to generate monthly means for 100 years from 1981 to 2080., The models were used to project trends for 4082 sites across England. They illustrate how river water temperatures rises may vary across the country and where important temperature thresholds for Atlantic salmon and brown trout may be exceeded. The project also explored whether the projections varied between different river types based on geology and land use.

1.3 Results

The average water temperature of the warmest summer month is projected to rise by about 0.6°C each decade. The projections indicate that adult brown trout will be under threat from high summer water temperatures at almost all sites by 2080 as their upper growth and feeding temperature range of 19.5°C could be exceeded.  Salmonid eggs survive best at winter temperatures below 12°C. This threshold could be exceeded at over 70% of sites by 2080.

The models developed for the various river types showed differences in the projected temperature, with arable/grassland sites on permeable rock experiencing the highest decadal changes in maximum temperatures (0.66°C per decade) and chalk streams the lowest (0.51°C per decade). Grass upland sites are projected to experience the warmest summer months by 2080 (>28°C) and chalk the coolest summer months (<26°C).

These monthly average daytime projections may not reflect local temperature variations and will miss short-term heatwaves, which may have important ecological effects. Future work to explore the value of less spatially extensive but more frequently sampled (e.g. daily) data will be useful. However, these projections are already proving useful as indicators of how temperature sensitive species may be affected and can be used to explore implications for water quality management.

1.4 Conclusions

Average monthly daytime river water temperatures are projected to increase throughout England affecting freshwater species and water quality. The effects will vary across different river types. With these new projections, the Environment Agency can assess how, where and to what degree warming may be of concern.

1.5 Publication details

This summary relates to information from the following project:

• Report: SC220018/R1
• Title: Water temperature projections for England’s rivers.
• Project manager: Judy England, Chief Scientist’s Group
• Research contractor: University of Birmingham

This project was commissioned by the Environment Agency’s Chief Scientist’s Group, which provides scientific knowledge, tools and techniques to enable us to protect and manage the environment as effectively as possible.

Enquiries: research@environment-agency.gov.uk.

© Environment Agency