Revisions to EA Climate Change Allowances

In July 2021, the Environment Agency (EA) revised their previously published climate change allowances.

Using UKCP18 projections, the EA update the peak river flow allowances basing them upon management catchments rather than river basin districts as was previously the case. Management catchments are sub-catchments of river basin districts.

The EA have also revised their guidance on how to apply the river basin flow allowances within Flood Risk Assessments and have simplified their approach. The majority of assessments will now only need to consider the ‘central allowance’.  The central allowance should also be able to calculate flood storage compensation, except where essential infrastructure is affected.




Climate change allowances

The climate change allowances for peak river flows are based upon percentiles and they show the anticipated changes to peak flow by management catchment. A percentile describes the proportion of possible scenarios that fall below an allowance level. The central allowance is based upon the 50th percentile, which is the point at which half of the possible scenarios for peak flow fall below it, and half fall above it.  Therefore, the central allowance is exceeded by 50% of the projections in the range.


For developments in Flood Zones 2 and 3 it will be necessary to determine the impact of climate change on rivers flows and assess the potential impact of flood risk over the developments lifetime as part of a Flood Risk Assessment.

Get in touch!

To speak with us further about how Cole Easdon can help with the assessment of climate change as well as the preparation of Flood Risk Assessments please contact: Dean Frosoni, Technical Director – / Tel: 01793 619965

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