Impacts and effects: Do we really understand the difference?

25th January 2012

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Jamie Gleave offers a practitioner's view on the differences between impacts and effects and how the terms are used in environmental impact assessments

The Environmental Impact Assessment (EIA) Directive (85/337/EEC) ensures that certain types of projects likely to have significant effects on the environment are subject to environmental assessment prior to approval or authorisation.

While the term “environmental impact assessment” describes the process undertaken, the EIA Directive calls for environmental effects to be identified and reported in an environmental statement, in order that decision-makers can be fully informed of the implications of proposals prior to granting development consent.

The wording throughout the EIA Directive places clear emphasis on the identification of environmental effects, with limited reference being made to identifying impacts, save for a brief mention in Article 7 and Annex III.

In undertaking EIA, it is commonplace for practitioners to correlate the sensitivity of the receiving environmental resource, or receptor, with the potential impact, to identify the environmental effect. The significance of an effect is then frequently determined by way of professional judgement and/or the use of matrices.

The definition and prediction of impacts and effects are, therefore, two separate aspects in the EIA process but which have a clear relationship with each other.

Seasoned EIA practitioners may have observed that it is routine in environmental statements and best-practice guidance for the terms “impact” and “effect” to be used interchangeably. This is more often a reflection of the author not wanting to use the same term repeatedly, rather than a deliberate attempt to use the terms in their correct context.

Given the purpose of the EIA Directive, and the liberal manner in which both terms can be used in EIA, this raises the important question of whether we really understand the difference between “impacts” and “effects” when undertaking and reporting EIAs.

Definitions of both terms vary depending on which literary source is referenced and in some established guidance there is a notable absence of a glossary explaining their meaning.

Where definitions are available in EIA guidance, the general consensus is that impacts are defined as the changes resulting from an action, and effects are defined as the consequences of impacts.

If, by way of example, we were to take a new bypass as a development proposal and the local landscape as the sensitive environmental resource, then an impact (the change arising from the development’s progression) could be the permanent loss of mature trees and hedgerows. An effect (the consequence of the impact), on the other hand, could be the opening of new views towards the new bypass or a change in the perception of local landscape character.

The distinction between the two terms in this example is fairly clear, however, for other environmental topics such as noise, this distinction can be much less apparent.

Matters are not helped by the fact that some topic-specific guidance does not provide a means of identifying and reporting significant environmental effects, or rather they require the significance of impacts to be established.

Difficulties can arise where technical specialists follow their own best-practice guidance and duly provide what they consider to be EIA compliant inputs to the project environmental coordinator. Faced with a package of reports by different authors – each reporting impacts and effects in their own particular way – the coordinator often feels obliged to rework assessments and terminology in an effort to try and establish a modicum of consistency across the EIA.

While it is never considered best-practice to attempt to change assessments that have relied on and followed best-practice guidance, the overarching requirement to report significant environmental effects under the EIA Directive remains. The identification and reporting of significant environmental impacts in an environmental statement could, therefore, be viewed as falling short of the requirements of the EIA Directive.

EIA, by its very name, implies we should be assessing impacts yet the content of the EIA Directive suggests otherwise. Genuine challenges therefore exist in terms of consistently defining what constitutes an “impact” and what constitutes an “effect” across a series of individual assessments.

When taking an overview of all the published guidance and standards that EIA practitioners currently operate under, the inconsistencies become clear and reveal a genuine problem in current EIA practice.

The accurate reporting of significant environmental effects within a multidisciplinary process can only really be achieved when there is a robust understanding of the two terms, and when topic-specific methodologies provide a means of consistently identifying and predicting them.

This article was written as a contribution to the EIA Quality Mark’s commitment to improving EIA practice.

Jamie Gleave is a principal EIA consultant at RSK Environment. He is a Chartered environmentalist and Chartered scientist a Full member of IEMA and a Full member of the Institution of Environmental Sciences.


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