Shedding light on the dark side

4th March 2016

EIA: Martin Broderick and Bridget Durning on improving assessment of cumulative effects

Five years ago cumulative effects assessment was portrayed as a ‘dark art’ and a ‘wicked problem’ by Canadian consultants George Hegmann and GA Yarranton. A review of current practice when applying it to offshore wind farms suggests the damning descriptions that emerged in that study still hold good now. This latest investigation revealed evidence of continuing problems, though there were signs of improvement, and found a lack of consistency in terminology and of transparency in the methodology used.

It recommends a three-pronged strategy to improve cumulative assessment: adoption of a clear definition of cumulative effects; further development of guidance, such as the cumulative effects assessment analytical framework developed by Oxford Brookes University for the Natural Environment Research Council (NERC); and the publication of more best practice case studies.

In law

Cumulative effects derive from a combination of multiple developments and events. Effects from a single development may not be serious on their own but, when combined with others, the result could be significant.

Oxford Brookes University, with support from the NERC, analysed eight nationally significant infrastructure projects (NSIPs) in England and Wales and two from Scotland to examine cumulative effects assessment (CEA) in the environmental impact assessment (EIA) and habitats regulations assessment (HRA) process.

The licensing procedures for infrastructure development require a CEA if the consequences of multiple projects or activities create an effect greater than or different from that of the individual projects. Although the requirement to consider cumulative effects before a development is established in EU EIA legislation, in practice it is complex and research suggests that practice is poor globally.

All proposals for projects that are subject to the EU EIA directive (2011/92/EU as amended) must be accompanied by an environmental statement (ES) that sets out the outcome of assessment of the likely significant environmental impact of the development.

The 2011 version of the directive refers specifically to the need to consider the effects of proposed projects and developments on ‘human beings, fauna and flora, soil, water, air, climate, the landscape and seascape, material assets and cultural heritage’. It requires the assessment of the likely significant effects, covering the direct and indirect ones, as well those that are secondary, cumulative, short, medium and long term, permanent and temporary, positive and negative at all stages of the project. It also demands that measures are set out for avoiding or mitigating significant adverse effects.

The habitats directive (92/43/EEC) requires that an appropriate assessment is performed if a plan or project is likely to have a significant effect on a Natura 2000 site – that is, a special area of conservation (SAC) designated under the directive or a special protection area (SPA) classified under the EU birds directive (2009/147/EC). The process of screening for likely significant effects and the undertaking of an assessment is known as an HRA.

Guiding principles

A Canadian review of CEA practice in 2013 highlighted areas for improvement. The researchers, from the School for Resource and Environmental Studies at Dalhousie University and ESSA Technologies, recommended that future guidance ought to focus on several factors, including:

  • defining concepts of cumulative effect – they suggest simple sentences are not sufficient and conceptual frameworks are required;
  • the use of scenarios and particularly an expanded definition of what are ‘reasonably foreseeable projects’;
  • the evolution of analytical methods need to be transparent in records of the outcome of assessment;
  • better collaboration between stakeholders and implementation of governance models, which need to be acknowledged and addressed;
  • the adoption of thresholds and balancing the precautionary approach;
  • strengthened follow-up and monitoring post consent; and
  • sharing of accumulated knowledge.

The wind energy industry identified the importance of these factors in 2013 in the Renewables UK publication Cumulative Impact Assessment Guidelines: guiding principles for cumulative impacts assessment in offshore wind farms. The guidelines set out 11 principles, which were developed by industry, regulators and stakeholders:

  1. CEA is a project level assessment, carried out as part of a response to the requirements of the EU EIA, habitats and birds directives, and designed to identify potentially significant impacts of developments and possible mitigation and monitoring measures.
  2. Developers, regulators and stakeholders should collaborate on the CEA.
  3. Regulators and their advisers should provide clear and transparent requirements for the CEA.
  4. CEA should include early, iterative and proportionate scoping.
  5. Boundaries for spatial and temporal interactions for CEA work should be set in consultation with regulators, advisers and other key stakeholders, and in line with best available data.
  6. Developers should use a realistic ‘project design envelope’ or parameters.
  7. Developers should consider projects, plans and activities that have enough information available in order to undertake the assessment.
  8. The sharing and common analysis of compatible data enhances the CEA process.
  9. CEA should be proportionate to the environmental risk of the projects and focused on key impacts and sensitive receptors.
  10. Uncertainty should be addressed and, where practicable, quantified.
  11. Mitigation and monitoring plans should be informed by the results of the CEA.

Clarifying terminology

It was the 2011 study Alchemy to Reason: effective use of cumulative effects assessment in resource management that described CEA as a ‘dark art’ and a ‘wicked problem’. It stated that CEA was ‘like forecasting weather or climate [because] the system under examination is complex and often responds to disturbance in a non-linear fashion’. CEA does suffer from ambiguous and sometimes confusing terminology (see below). There are many definitions of cumulative effects, depending on the context.

Best practice should be to clearly set out the concepts and definitions of CEA. The Oxford Brookes NERC-funded project includes a short definition to guide practice and to help bring some transparency to the complex ‘dark art’ of CEA. It defines cumulative effects as ‘those that result from additive effects caused by other past, present or reasonably foreseeable actions together with the plan, programme or project itself … and synergistic effects, which arise from the reaction between effects of a development plan, programme or project on different aspects of the environment’. In other words, cumulative effects are those added by or that result from the interaction of two or more projects or activities.

This definition is also included in the Renewables UK guide as well as in the BSI guide to EIA for offshore renewable energy projects (PD6900: 2015). The BSI publication is free and covers undertaking EIA for offshore wind, wave and tidal projects. It focuses on the main component of the offshore renewable energy project rather than supporting infrastructure and covers all the elements of the EIA process, such as screening, scoping, determining environmental impacts and the environmental statement. It also addresses mitigation and monitoring plans, consultation and communication.

In legislation, regulations, industry and in practice, the terms ‘impacts’ and ‘effects’ are often used interchangeably. However, they are different. To use the analogy of the hammer hitting and breaking a mirror, the ‘impact’ is the tool hitting the glass, while the ‘effect’ is the broken glass on the floor. The difference needs to be recognised and it is worth noting that the EU directives tend to use effects. Nonetheless, the language used in the EIA and SEA (strategic environmental assessment) directives has caused practitioners and regulators considerable confusion. Adoption of the terms ‘additive’ and ‘synergistic’ as used in the definition above should help to clarify the situation, and these two types of cumulative effects should be considered when performing a CEA.

Analytical framework

As part of the university’s research, an analytical framework has been developed to ensure that all relevant issues have been included in the assessment process. It follows 10 steps:

  1. Clearly explain the definition of cumulative effects being applied. Identify likely significant CEA aspects associated with the proposed project or plan and define approach.
  2. Establish temporal and spatial limits – spatial can be different in noise, air quality, landscape and visual impact assessment, for example.
  3. Identify other past, present and reasonably foreseeable future projects that could affect receptors (long list) – valued ecological components, humans and resources.
  4. Establish sensitivity of receptors and define thresholds.
  5. Define and describe the baseline.
  6. Establish source-pathway-receptor (short list) and consult on the list, giving reasons for dropping projects from the long list (stage 3).
  7. Assess significance of effects – cumulative, additive and synergistic.
  8. Modify or add alternatives or propose mitigation to avoid or reduce cumulative effects.
  9. Detail the uncertainty and limitations in the assessment.
  10. Monitor and manage using an environmental management plan.

Driving practice

The Oxford Brookes University research has identified that CEA practice is improving and evolving. Key to driving forward practice has been the requirements made by decision-makers and statutory stakeholders at the scoping stage, particularly due to the Planning Act 2008. Practitioners are also being more transparent in their methodologies, which will aid others to reflect on their own practice and to innovate. Examples of good practice will help this. Improving assessment practice, which is based on transparent methodology and robust evidence, will also assist the decision-makers.

The use of a clear definition, the continuing development of guidance, such as the CEA analytical framework, and the publication of case studies of best practice should all help to improve CEA further and take it out of the dark.

Confusing terminology in law

Additive effects – those that result from additive effects caused by other past, present or reasonably foreseeable actions, together with the plan, programme or project itself

  • EIA Directive (2011 version) refers to these as ‘cumulative effects’.
  • European commission/Hyder (1999) guidance refers to these as ‘cumulative impacts’.
  • SEA directive refers to these as ‘cumulative impacts’.
  • EU habitats directive refers to these as ‘in-combination’ effects.

Synergistic effects – these arise from the reaction between effects of a development plan, programme or project on different aspects of the environment

  • EIA Directive (2011) refers to these as ‘interrelationships’ and effect ‘interactions’.
  • European commission/Hyder (1999) guidance refers to these as ‘impact interactions’.
  • SEA directive refers to these as ‘in-combination or synergistic’ impacts.
  • EU habitats directive does not refer to these separately.


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