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Member Briefing: Revised climate change allowances issued by EA

Date: 06/04/16

Revised climate change allowances issued by EA

Information note based on teleconference call between HBF & EA surrounding REVISED CLIMATE CHANGE ALLOWANCES issued by EA on 19/02/16





1.     Background

On the 19th February 2016 the Environment Agency issued revised climate change allowances for use in flood risk assessments. These latest changes, based on the most up to date science-based research, are to apply with immediate effect, but with the following exceptions, i.e. accepted ‘temporary’ transitional arrangements:

a)    Where a local development plan has already been submitted for examination. Post discussion comment: It is likely that Neighbourhood Plans that have reached the ‘referendum stage’ will also fall into this category – but see later comments.

b)    Where a valid/validated planning application has already been submitted to the Local Planning Authority (LPA)

c)    Where planning consent (outline/detailed) already exists but see later comments relating to the timing/longevity of outline planning consent(s)

Important Note: For developments that are particularly sensitive to flood risk and/or situated in a vulnerable location, then the EA will base its advice on the updated allowances.

Prior to today’s telephone conference between the HBF and the EA, a number of HBF Members had raised concerns about the likely impact of these latest changes, in particular when dealing with longer term strategic land. This file note not only reflects discussions around the key concerns raised to date but also the response to such from the EA, together with confirmation of the EA’s position. That said, the EA caveated its response as follows:

“For developments in sensitive locations, i.e. vulnerable to potential climate change effects and that have already been submitted for planning permission, or have been approved as a development allocation in a local plan, then the EA would wish to engage with developers/LPAs to investigate the potential impact of the updated climate change allowances on flood risk. Similarly, to ensure that in such instances the design of the development includes appropriate flood risk mitigation”.

2.     Summary of the Discussion & the EA’s Response(s)   

a)    It is accepted that Hydrology is not an exact science but these latest climate change allowances reflect current best practice based on the latest credible scientific evidence from UKCP09.

b)    The EA has a strategic overview role of all flood risk matters and also remains a statutory consultee when development is to take place in Flood Zones 2, 3 and in areas where there are critical surface water drainage problems.

c)    Lead Local Flood Authorities (LLFAs): Operate within the 152 County and/or Unitary Authorities where they retain an overview of flood risk matters relating to surface water, ordinary watercourses and groundwater.

In addition, since April 2012, they have been required to play an advisory, albeit non-statutory role in the preparation of Strategic Flood Risk Assessments (SFRAs) – the Local Planning Authority is responsible for producing a SFRA. (See Paragraph 011: Ref ID 7-011-20140306 Planning Practice Guidance: Strategic Flood Risk Assessment – 6th March 2014)

d)    SFRAs are key flood risk assessments that are expected to play a crucial role in the planning process by providing risk-based assessments that allow Local Planning Authorities (LPAs) to make informed decisions when considering Local Plan ‘land use’ allocations and/or when determining planning applications.

e)    SFRAs use baseline flood risk data provided by the EA. LPAs use this baseline data, together with the climate change allowances guidance provided by the EA to model future flood risk in their SFRA. There are two levels of SFRA, namely, Level 1 (generic but with enough detail for the sequential test to be applied) and Level 2 (area/site specific in response to increased flood risk potential, and containing enough detail for the exception test to be applied).

f)     On April 15th 2015, LLFAs became statutory consultees for surface water management for major development applications. (Major development is defined by DCLG as 10 dwellings or more).

HBF Member Advisory Note: A proposed surface water drainage strategy for a new residential development site may require the approval of the EA, LLFA or Internal Drainage Board (IDB) – this should be verified at the pre-application discussion stage. In most cases this will fall to the LLFA but the EA are likely to have an interest if development is within an area of critical drainage problems, or if the EA had imposed/recommended planning conditions on an earlier consent that they in turn would recommend and/or confirm the discharge thereof.

g)    At the same time the NPPF was published (2012) the existing climate change allowances were published in Technical Guidance supporting the NPPF. During 2012/13 DCLG carried out a complete review of existing planning guidance. New, web-based planning practice guidance was introduced – this superseded all earlier technical guidance. In 2013 the EA agreed to publish the climate change allowances as separate advice before the earlier technical advice was cancelled and replaced with new Planning Practice Guidance in March 2014. The EA published the existing allowances at the time to ensure continuity in the transition to new the Planning Practice Guidance. In late 2013 the EA commenced work on preparing new climate change allowances guidance – the latest ‘allowances’ stem from this work. Moreover, they are expected to help planners and developers comply with existing planning policy. 

h)    DCLG remain responsible for the NPPF and supporting NPPG – any questions about changes to the policy or guidance are to be addressed to DCLG.

i)      The EA confirmed that these latest changes should have relatively little difference in impact on assessed future flood risk in the short to medium term, i.e. up to the 2050’s, compared to assessments using the previous allowances. In many locations and/or development scenarios the impact should be ‘manageable’ with little deviation from established practices and/or outcomes.

j)      The EA will keep the ‘allowances’ up to date with new scientific understanding of how climate change is likely to affect future flood risk at a strategic level.

Flood risk assessment/mitigation advice provided for individual developments and/or Local Plans by local EA teams will be based on the most up to date climate change allowances guidance.

k)    The EA has confirmed that existing EA Flood Maps that support the planning process will not be affected by these latest revisions and can still be relied upon as part of the site specific flood risk assessment process. The underlying accuracy of these maps has not been compromised. The maps are not a replacement for site specific assessments of flooding constraints and provide an indication of the likelihood of flooding in certain locations.

l)      The latest revisions to climate change allowances are unlikely to have a material effect on most SFRAs. That said, some LPAs may subsequently seek to introduce amendments to existing SFRAs based on updated hydraulic modelling to reflect the new climate change allowances. The EA do not believe that existing SFRAs are no longer reliable in the context of the new climate change allowances being introduced. This is because the application of the sequential test will have steered development to land at lowest risk of flooding. Sites allocated based on a SFRA using previous allowances are expected to be accompanied by a FRA that uses the updated climate change allowances. From here on, any updated SFRAs will need to reflect the latest climate change allowances. 

m)   The question has been posed as to what is an appropriate lifetime for a development when considering potential flood risk? In response the EA confirmed that there has been no change to current NPPF recommendations, i.e. 100 years for residential development and potentially less for commercial buildings but dependent upon location relative to known flood risk. Any mixed use scheme involving housing would default to a 100-year design life.

n)    The changes in peak rainfall intensity allowance are not considered to be all that significant and therefore manageable. To assist HBF members, Table 1 below has been provided – this compares the earlier peak rainfall intensity with the latest climate change allowances introduced by the EA on 19th February 2016. This comparison shows that there has been a subtle change in the ‘epoch’ timescales.




1990 to 2025

2025 to 2055

2055 to 2085

2085 to 2115

Peak Rainfall Intensity





19th Feb 2016 Change



2010 to 2039

2040 to 2059

2060 to 2115

Peak Rainfall Intensity





Table 1 – Peak Rainfall Intensity: Impact of 2016 Climate Change Allowances

o)    The EA has advised that for applications where the EA is a statutory consultee and has an interest in the control of surface water run-off in new developments, i.e. in areas with critical drainage issues, then for developments with a 100-year design life, the EA would typically recommend that the central estimate (20%) is used for design purposes when considering the impact on surface water drainage networks, i.e. an assessment of the performance of the drainage system in order to check that the system can cope with the critical duration design rainfall event.

The EA further recommends that the upper end estimate (40%), should be used to assess the potential flood risk implications arising from the critical duration design rainfall event to test the following – (a) is surface water wholly contained on site? (b) is there an increased flood risk to third parties? (c) Is any flood hazard within acceptable tolerances? (d) Can the system cope?

p)    Outline planning consents will have been granted for sites in the past 3 years with conditions based on previous climate change allowances.

q)    When consulted on reserved matters applications for sites with an existing outline planning consent (prior to publication of the updated climate change allowances), the EA will take a risk based approach to securing flood risk mitigation in the context of the updated climate change allowances. This will also respect any parameters set by the conditions attached to the outline consent.

For example, if a condition specified a ‘30% increase in peak rainfall intensity to account for the impacts of climate change’ then that is what the system would need to be design to, whereas if the condition was more loosely worded and just referred to ‘take into account the impacts of climate change’ then the EA would likely request that the system should be designed to the new 40% allowance – see paragraph (o) previous. 

r)     Therefore, for future large strategic sites, i.e. over 1000 dwellings there is merit in seeking planning conditions on outline planning consents that crystallise the current/ agreed design conventions in terms of flood risk assessment, in particular specified peak rainfall intensity criterion. Thereafter, these agreed conventions can be applied consistently throughout future phases of the development, in particular when reserved matters approvals are being sought.

s)     During these discussions the EA confirmed that surface water exceedance may be contained within residential estate roads and open space areas providing the depth of surface water inundation is limited, i.e. contained within the carriageway/open space area and for relatively short periods. That said, there is an important caveat in that the EA are no longer statutory consultees and the surface water strategy/management approach will need to be agreed with the relevant LLFA for each development. 

Further Advice for HBF Members

Clearly, the need to engage in pre-application discussions with those bodies responsible for advising and dealing with all aspects of flood risk and flood risk mitigation is essential. Moreover, at the important land acquisition stage, land purchase contracts that are conditional upon securing approval to an appropriate and satisfactory surface water drainage strategy equip house builders with improved commercial protection.  


HBF London

1st March 2016