SEPA Climate Change Allowances in Scotland

In April 2024, SEPA updated their guidance with regard to peak flow and rainfall estimates and the additional allowance to account for climate change.

Coastal allowances are unchanged from the previous guidance.

Up until 2018, SEPA required a universal 20% allowance to account for climate change before the publication of Version 1 of the “Climate Change Allowances for Flood Risk Assessment in Land Use Planning” document.

Version 2 of the document now includes revisions to the impacts of climate change on both river flow and rainfall, based on the latest UK Climate Projections 2018 for Flood Risk Assessments in Scotland.

This latest guidance document includes climate change projections up to the year 2100 and the predicted impact to both river flows and total rainfall — for the 12 River Basin Regions in Scotland.

What Are The Revised Climate Change Allowances?

The required allowance for climate change for peak river flow estimates shows an average increase of 9% across all regions. This allowance must be accounted for all peak river flow estimates that have:

1. Catchment areas greater than 50km2 (excluding catchments in Orkney and Shetland)
2. Catchment areas (excluding Orkney and Shetland) between 30km2 — 50km2 where the peak river flow uplift is larger than the flow increase

The Tweed River Basin (which previously required a 33% additional allowance for river flows due to climate change), now requires a 59% increase, the largest value to rise with this recent update.

SEPA notes that peak river flow allowances for both Orkney and Shetland are not available, as all river catchments in these areas are less than 100 km2, and using peak rainfall allowances is recommended.

For river catchments smaller than 30km2, and for surface water flooding issues, SEPA recommends peak rainfall intensity allowances be applied for the relevant River Basin.