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Update to Environment Agency ‘Flood risk assessments: climate change allowances’

What this is about

On 20 July 2021 the peak river flow allowances in ‘Flood risk assessments: climate change allowances’ were updated so they reflect the latest projections in UKCP18 and subsequent research that models how the latest rainfall projections are likely to affect peak river flows.

The main changes include:

  • Change to how peak river flow allowances are provided from by river basin district to a smaller geography called management catchments. This means the allowances better reflect variability in how different catchments will respond to the impact of climate change.
  • How the peak river flow allowances are applied is also changing, focusing more on use of the central allowance.
  • Reflecting variability within catchments means allowances will be lower than the current allowances in some places, but also they will be higher in others. Focus on use on the central allowance will ameliorate the impact where updated allowances are higher than the previous allowances.

Latest climate science and research shows peak river flows could more than double by 2100 in some locations. By ensuring our guidance is premised on the latest climate change projections, it promotes resilient and sustainable communities and built environment, helping local planning authorities and developers to demonstrate they are prepared for the climate emergency.

This update supports the Environment Agency goal for ‘a nation resilient to climate change’

In our corporate plan ‘EA 2025’ we state our ambition to be a stronger leader on climate adaptation and resilience, encouraging others to act now on the climate emergency and invest in adaptation.

The guidance promotes a robust approach to climate resilience, based on the high emission scenario of UKCP18, with the central allowance representing a 4°C increase by 2100. This ensures our approach is grounded on the latest evidence on the global climate change pathway we are currently following, reflected in UNEP Adaptation Gap report (Jan 2020), which states we are heading for a 3°C temperature rise this century, but this could be as high as 4°C.

Future updates

The allowances for sea level rise were updated based on sea level rise projections in UKCP18 in December 2019.  The allowances for peak rainfall are unchanged for the time being. This is because high resolution rainfall projections were published later as part of UKCP Local (2.2km) in September 2019. Research is underway to develop peak rainfall allowances from the projections in UKCP Local, which is due to be published summer 2021. Once this research has been published we will start work to understand if and how the peak rainfall allowances need to be updated.

Guidance for flood and coastal erosion risk management schemes and strategies

The peak river flow allowances have also been updated in Environment Agency guidance ‘Flood and coastal risk projects, schemes and strategies: climate change allowances’ using a similar approach. Contact Andrew Eden ( for a separate briefing explaining the update to this guidance.

Contact for further information

If you have any questions about the update to ‘Flood risk assessments: climate change allowances’ please contact Caroline Sutton.

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