Climate change and peak river flows

Climate change impacts on peak river flows

Alison L Kay ¹, Ali Rudd ¹, Matthew Fry ¹, Gemma Nash ² and Stuart Allen ³

¹ UK Centre for Ecology & Hydrology, Wallingford, United Kingdom

² UK Centre for Ecology & Hydrology, Edinburgh, United Kingdom

³ Environment Agency, United Kingdom

The Climate change and fluvial flood peaks research investigated how climate change affects fluvial flood peaks. The evidence is used to support sustainable development and investment in flood and coastal risk mitigation actions. The research spanned from 2018 to 2021 and was published in 2023.

The research builds on past projects. In 2010, the early uplifts were assessed in the Regionalised impacts of climate change on flood flows, which used selected local hydrological models within a sensitivity framework. The hazard was regionalised using UK climate projections (UKCP09) in Practicalities for implementing regionalised allowances for climate change on flood flows. However, in this earlier research, the information on the impact of flooding relied on old climate projections and was based on modelling a limited number of locations.

The release of updated UK climate projections (UKCP18) paired with new, national scale modelling methods, offered an opportunity to improve the information available for decision-making. The team combined the sensitivity framework with a national-scale hydrological model (Grid-to-Grid) and the UKCP18 probabilistic projections in the 2023 publication. This enabled a better understanding of potential changes to flood peaks across every 1km square of the river network in England, Wales and Scotland. In doing so, it helped to address the limitation that previous uplifts were derived from a limited number of specific catchment models. By using a consistent approach, the research team discovered varying sensitivities among catchments. This discovery helped predict how different regions would respond to climate-induced rainfall changes.

Impact

The research results had significant implications for flood risk management. The data produced provided more nuanced understanding of how flood peaks may change. This enabled the Environment Agency to update guidance for estimating future flood risks aimed at building developers and flood risk management authorities.

The Environment Agency’s Director of Strategy and Adaptation (2021) said: “[w]e now have much more detail than ever before on how river flows will change at a catchment level, allowing us to address future flood and coastal risks more confidently.”

The findings were integrated into national guidance for flood risk assessments. This ensured that developers accounted for climate change in their planning processes. Between April 2023 and March 2024, over 96% of planning decisions adhered to flood risk advice based on these updated guidelines, which demonstrated effective uptake of the research outputs.

The Flood and Coastal Erosion Risk Management report: 1 April 2023 to 31 March 2024 illustrated how the guidance helped avoid potentially unsafe developments. In particular, 60,000 homes were protected through adherence to the updated flood risk advice.

The Environment Agency’s Chief Scientist Group’s Annual Report 2022 highlighted the successful integration of research findings into operational practices.

The insights gained from this research provided a crucial foundation for future planning and flood risk management. For those involved in planning and flood risk management, it is vital to consult the updated guidance for conducting flood risk assessments.

Resources

Department of Environment, Food and Rural Affairs (Defra). (2025). Climate change allowances for peak river flow. Available at: https://environment.data.gov.uk/hydrology/climate-change-allowances/river-flow. (Accessed: 24 March 2025).

Environment Agency. (2016). Flood risk assessments: climate change allowances. Available at: https://www.gov.uk/guidance/flood-risk-assessments-climate-change-allowances (Accessed: 24 March 2025).

Environment Agency. (2020). Flood and coastal risk projects, schemes and strategies: climate change allowances. Available at: https://www.gov.uk/guidance/flood-and-coastal-risk-projects-schemes-and-strategies-climate-change-allowances (Accessed: 24 March 2025).

Environment Agency. (2021). Practicalities for implementing regionalised allowances for climate change on flood flows. Available at: https://www.gov.uk/flood-and-coastal-erosion-risk-management-research-reports/practicalities-for-implementing-regionalised-allowances-for-climate-change-on-flood-flows (Accessed: 24 March 2025).

Environment Agency. (2021). Regionalised impacts of climate change on flood flows. Available at: https://www.gov.uk/flood-and-coastal-erosion-risk-management-research-reports/regionalised-impacts-of-climate-change-on-flood-flows (Accessed: 24 March 2025).

Environment Agency. (2021). Managing flood risk in the face of a changing climate – Creating a better place blog. Available at: https://environmentagency.blog.gov.uk/2021/07/20/managing-flood-risk-in-the-face-of-a-changing-climate/ (Accessed: 24 March 2024).

Environment Agency. (2023). Climate change and fluvial flood peaks. Available at: https://www.gov.uk/flood-and-coastal-erosion-risk-management-research-reports/climate-change-and-fluvial-flood-peaks (Accessed 24 March 2025).

Environment Agency. (2023). Chief Scientist’s annual review 2022. Available at: https://assets.publishing.service.gov.uk/media/63ff3f57d3bf7f25f76ffc9d/Environment_Agency_Chief_Scientist_s_annual_review_2022.pdf (Accessed: 24 March 2025).

Environment Agency. (2024). Flood and coastal erosion risk management report: 1 April 2023 to 31 March 2024. Available at: https://www.gov.uk/government/publications/flood-and-coastal-risk-management-national-report/flood-and-coastal-erosion-risk-management-report-1-april-2023-to-31-march-2024 (Accessed: 24 March 2025).

Kay, A.L., Rudd, A.C., Fry, M., Nash, G. and Allen, S. (2021). Climate change impacts on peak river flows: Combining national-scale hydrological modelling and probabilistic projections. Climate Risk Management. Vol 31. Available at: doi.org/10.1016/j.crm.2020.100263 (Accessed: 24 March 2025).

Met Office. (2021). Met Office UKCP18 case study. Available at: https://www.metoffice.gov.uk/binaries/content/assets/metofficegovuk/pdf/research/ukcp/ceh_ukcp_case_study.pdf (Accessed: 24 March 2025).

Ministry of Housing, Communities and Local Government. (2014). Guidance: Flood risk and coastal change. Available at: https://www.gov.uk/guidance/flood-risk-and-coastal-change (Accessed: 24 March 2025).

Reynard, N. S., Kay, A. L., Anderson, M., Donovan, B., & Duckworth, C. (2017). The evolution of climate change guidance for fluvial flood risk management in England. Progress in Physical Geography, 41(2), 222-237. Available at: doi.org/10.1177/0309133317702566 (Accessed: 24 March 2025).

UK Centre for Ecology & Hydrology (UKCEH). (2025). Climate change impacts on river flood peaks. Available at: https://cc-flood-impacts.ceh.ac.uk/ (Accessed: 24 March 2025).

Wasko, C., Westra, S., Nathan, R., Orr, H.G., Villarini, G., Villalobos Herrera, R. and Fowler, H.J. (2021). Incorporating climate change in flood estimation guidance - Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. Phil. Trans. R. Soc. A. 379: 20190548. Available at: doi.org/10.1098/rsta.2019.0548 (Accessed: 24 March 2025).

Funder

The research project was funded by the Flood and Coastal Erosion Risk Management (FCERM) research and development programme.

Collaborators

• Environment Agency
• UK Centre for Ecology and Hydrology
• Natural Resources Wales
• Scottish Environmental Protection Agency

Research period

• 2018 to 2021

Impact period

• 2021 to present

Impact country

• England
• Scotland
• Wales

Contributing to the areas of research interest

• 1 - Understanding future flood and coastal erosion risk