QMark: Cumulative environmental assessment

7th July 2020

The team at ASH Design + Assessment discusses some of the difficulties in carrying out cumulative environmental assessment

Cumulative environmental assessment (CEA) is an important element of the environmental impact assessment (EIA) process, particularly for larger-scale developments where environmental effects could 'overlap' those of other developments. Despite the extensive use of CEA in EIA, there are often inconsistencies and difficulties in its execution.

Uncertainties in assessment

CEA is a standard requirement requested by consultees during EIA consultation, outlining the particular receptors to take into consideration within their respective remits. In some instances, the applicant will be directed towards particular guidance, which can be specific to the development type and receptor (eg Scottish Natural Heritage's guidance on Assessing the cumulative impacts of onshore wind farms on birds), or more generalised (eg the Landscape Institute's Guidelines for Landscape and Visual Impact Assessment). However, in most cases the applicant is simply instructed to consider cumulative effects, without specific direction.

There is a general understanding of what is expected within a CEA: for a given impact assessment, the assessor should identify nearby 'like' developments that could also affect the receptor under consideration, and determine the magnitude of their impact in combination. However, uncertainties can crop up when considering issues such as:

  • Spatial extents – to what distance from the proposed development should the assessor consider other developments, and how does this vary between environmental disciplines?
  • Temporal extents – should a given impact be considered cumulatively for the construction stage only, the lifetime of the project, or beyond (residual effects following decommissioning and restoration)?
  • Planning system – is it appropriate to include only those developments that have also been subject to a full EIA?
  • What are considered to be 'like' developments – should only developments of the same type be considered (eg wind turbines above a certain height), or should this be more specifically defined by environmental discipline, such as including other tall structures in the visual impact assessment, or those with similarly large footprints when considering flood risk?

IEMA recently published an article on the key challenges facing the EIA community with regard to CEA, concluding that ongoing dialogue is required to help define a commonly agreed and replicable approach. One area the article touched on that is less often used in CEA is the practice of intra-relationship assessment.

Inter and intra-relationship assessment

Inter-relationship assessment is the commonly employed CEA, where the effects of two or more distinct developments upon an environmental receptor are considered. Intra-relationship assessment, considers the differing effects of a single development on a receptor – specifically, whether effects considered to be non-significant within individual assessments could result in a significant cumulative impact.

For instance, a hypothetical wind farm is proposed 3km from a private residence. A full EIA has been carried out following established guidance, and no individual significant effects are identified at the residence for the construction phase of the development. However, the combined effects of noise, dust, traffic and visual effects occurring simultaneously during construction of the wind farm could be considered significant.

As the EIA for each environmental discipline is generally carried out separately by specialists – and tied together by the EIA coordinator – intra-relationship effects are less readily apparent. This is compounded by the lack of industry guidance on this type of assessment, leaving assessors to rely on professional judgment and previous experience.

Further uncertainties exist in addition to those mentioned above. Who is best placed as the 'competent expert' to carry out this assessment in line with the EIA Regulations? How should different types of effects be compared? Would a methodology for determination of significance have to be established for each individual receptor or type of receptor? Dust generation would likely be a greater issue for a private residence than a wetland habitat, and otters would not be bothered by disrupted television signal, but how does an assessor determine if a minor visual effect is equivalent to a minor noise effect? When 'tallying up', should greater weight be given to some effects than to others? In the absence of specific guidance, intra-relationship assessment will vary across the industry, creating a more difficult position for decision-makers when reviewing.


Despite the legislative requirements for CEA to be carried out within EIA, and the various guidance documents available, assessors can still encounter uncertainties in the application of cumulative assessment across different projects. This is particularly true in the case of intra-relationship assessment, which relies heavily on professional judgement and previous experience rather than any form of standardisation. Specific challenges lie in defining methodologies for intra-relationship assessment, especially where distinctions between different types of effect on a receptor are less intuitive, and further dialogue is required within the industry to shape and define how this should be approached.

ASH Design + Assessment is a Glasgow-based provider of professional landscape design and environmental assessment services.

Image credit: iStock


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