EA Climate Change Allowances 2026: What Changed and Why It Matters

The Environment Agency periodically updates its climate change allowances for flood risk assessments — the percentage increases that must be added to peak river flow, peak rainfall intensity, sea level rise, and offshore wind speed to account for the projected effects of climate change over the design life of a development.

The latest update, published in early 2026, introduces revised uplift percentages for several river basin districts and clarifies the application of allowances to different development types. These changes have direct implications for every flood risk assessment submitted in England, and failing to apply the correct allowances is one of the most common — and most avoidable — grounds for EA objection.

This article explains what changed, why it matters, and how to apply the updated allowances correctly.

What Are Climate Change Allowances?

Climate change allowances are the percentage increases that must be applied to present-day flood parameters to account for the projected effects of climate change. They recognise that flood risk is not static — as the climate changes, flood risk is expected to increase in most parts of England.

The allowances are provided at three levels:

• Central estimate: The midpoint of the projected range. Used for some assessments but not typically the primary design basis for residential development.
• Higher central estimate: A higher projection that represents a more precautionary view of future risk. Used for some development types and some planning purposes.
• Upper end estimate: The highest projection, representing the upper bound of the projected range. This is the primary design basis for residential development (more vulnerable uses) with a design life extending to the 2080s or beyond.

The allowances vary by:

• River basin district: Different parts of England are projected to experience different levels of change, reflecting regional climate projections and hydrological characteristics.
• Epoch: The time period being assessed. Climate change projections increase over time, so the allowances are higher for the 2070-2125 epoch than for the 2025-2060 epoch. The relevant epoch depends on the design life of the development.
• Parameter: Separate allowances are provided for peak river flow, peak rainfall intensity, sea level rise, and offshore wind speed.

What Changed in 2026?

The 2026 update introduces several important changes:

Revised Peak River Flow Allowances

The most significant change is the revision of peak river flow allowances for several river basin districts. The updated allowances reflect the latest UK Climate Projections (UKCP) data and improved hydrological modelling of how climate change translates into changes in river flows.

Key changes include:

• Increased upper end allowances for several river basins in the north of England and the Midlands. River basins that were already projected to see significant increases in peak flow have had their upper end allowances raised further, reflecting updated climate science that suggests greater sensitivity to climate change in these catchments.
• Reduced allowances in a small number of southern and eastern river basins. Some river basins in the south and east of England have seen modest reductions in their upper end peak flow allowances, reflecting improved understanding of the relationship between rainfall and river flow in drier catchments. However, these reductions should be treated cautiously — they do not mean climate change risk is decreasing in these areas, but rather that the previous projections were slightly overstated.
• New allowances for previously ungrouped watercourses. Some smaller watercourses that were previously covered by default national allowances have been assigned river basin-specific allowances based on new modelling.

Updated Peak Rainfall Intensity Allowances

Peak rainfall intensity allowances, which are used for surface water drainage design and direct rainfall modelling, have also been updated. The key change is an increase in the upper end allowance for the 2070-2125 epoch in most parts of England, reflecting the latest evidence on how climate change is expected to affect the intensity of heavy rainfall events.

For drainage design, this means that attenuation storage volumes calculated using the previous allowances may be insufficient under the updated guidance. Any drainage strategy using the previous rainfall allowances should be checked against the new figures.

Clarified Application to Different Development Types

The 2026 guidance provides clearer direction on which level of allowance (central, higher central, or upper end) should be applied to different development types and planning scenarios:

• Residential development (more vulnerable): Upper end allowance for both flood risk assessment and drainage design. This was already common practice but is now explicitly stated.
• Commercial development (less vulnerable): Higher central allowance is typically appropriate, though the upper end should be used for sensitivity testing.
• Essential infrastructure: Upper end allowance, with sensitivity testing for the high-end (H++) scenario where available.
• Outline applications: Upper end allowance should be applied at outline stage to establish the principle of development. Detailed design at reserved matters stage can refine the allowance if justified.

Why It Matters

For Flood Risk Assessments

Every flood risk assessment submitted after the update must use the new allowances. Submitting an FRA with the previous allowances will trigger an EA objection, requiring the assessment to be revised and resubmitted — adding weeks or months to the programme.

For sites where the FRA includes hydraulic modelling, the model may need to be re-run with the updated allowances. This is particularly important for peak river flow changes, which directly affect modelled flood levels, extents, and depths. If the updated allowances are significantly different from those used in the model, the results may change materially.

For Drainage Design

Updated peak rainfall intensity allowances mean that attenuation storage calculations must be revised. A drainage scheme designed to the previous allowances may not provide sufficient storage under the updated figures, and the design may need to be amended to provide additional attenuation volume.

This has cost implications — additional storage means larger SuDS features, larger underground tanks, or more land allocated to attenuation. It is better to discover this at the design stage than at the planning consultation stage, when the LLFA points out that the drainage calculations use outdated allowances.

For Mitigation Design

Climate change allowances directly affect mitigation measures such as finished floor levels, compensatory storage volumes, and safe access routes. If the updated allowances produce higher flood levels, finished floor levels may need to be raised, compensatory storage volumes may need to increase, and access routes may need to be reassessed for flood depth and hazard.

How to Apply the Updated Allowances

Step 1: Identify the Relevant River Basin District

Determine which river basin district your site falls within. The EA publishes maps of river basin district boundaries, and the flood risk assessment should identify the relevant district. For sites near river basin district boundaries, check whether the allowances differ between adjacent districts and apply the more conservative figure if there is any ambiguity.

Step 2: Determine the Design Life and Epoch

The design life of the development determines which epoch’s allowances to apply:

• Residential development: 100-year design life. If the development is built in 2026, the assessment must consider conditions through to 2126, requiring the 2070-2125 epoch allowances.
• Commercial development: 60-year design life. A 2026 development requires consideration through to 2086, straddling the 2040-2069 and 2070-2125 epochs.
• Infrastructure: Variable design life depending on the type of infrastructure. Essential infrastructure often requires a design life of 100+ years.

Step 3: Select the Appropriate Allowance Level

Apply the correct level of allowance (central, higher central, or upper end) based on the development type and the purpose of the assessment:

• For the primary flood risk assessment of residential development: upper end.
• For sensitivity testing: higher central (to show the range of outcomes).
• For drainage design for residential development: upper end.

Step 4: Apply to the Modelling or Assessment

For FRAs with hydraulic modelling, apply the peak river flow allowance as an increase to the inflow hydrograph. For drainage calculations, apply the peak rainfall intensity allowance as an increase to the design rainfall. For sea level rise, apply the additive value to the tidal boundary conditions.

Step 5: Document the Allowances Used

Clearly state in the FRA which allowances have been used, the source (EA guidance title and date), the river basin district, the epoch, and the rationale for the selected allowance level. This transparency makes the EA’s review straightforward and reduces the risk of queries.

Transitional Arrangements

The EA typically provides a transitional period during which FRAs submitted using the previous allowances will still be accepted, provided the assessment was substantially complete before the update was published. However, this transitional period is limited — typically three to six months — and any new FRA commission should use the updated allowances from the outset.

If you have an FRA in progress that uses the previous allowances, check with your consultant whether the updated allowances affect the results materially. If they do, it may be worth updating the assessment before submission to avoid an EA objection.

Key Takeaways

• Check the current allowances before every FRA. The EA updates allowances periodically, and using outdated figures is a common ground for objection.
• Use the upper end allowance for residential development. This is now explicitly required, not just recommended.
• Update drainage calculations. Peak rainfall intensity allowances have increased in most areas, potentially requiring additional attenuation storage.
• Allow time for model updates. If your FRA includes hydraulic modelling, the model may need to be re-run with the new allowances.
• Document everything. Clearly state which allowances you have used and why.

If you need help understanding how the updated climate change allowances affect your project, or if you have an FRA in progress that may need updating, contact us. We will review the implications and advise on the most efficient way forward.