2. Prediction, evaluation and mitigation: the basics

Assessment, evaluation and mitigation are closely interlinked, as shown in the figure below.


The impact of a strategic action is the difference in environmental/sustainability conditions with and without the strategic action. Typical stages in impact prediction are thus:

  • Predict what the strategic action (and alternatives) would 'look' like, for instance:
    • what activities would probably occur?;
    • where would those activities probably occur?; and
    • when would they probably occur?
  • Determine, for each environmental/sustainability indicator, the geographic area over which the predictions are being made, and the timescale for the prediction. This can vary from impact/indicator to impact/indicator.
  • Estimate the likely changes to the environmental/sustainability baseline caused by the activities resulting from the strategic action (and alternatives):
    • direct impacts;
    • indirect impacts;
    • induced or generated impacts;
    • cumulative impacts;
    • impacts at different scales; and
    • impacts at different times.
  • Analyse the likely changes in terms of:
    • magnitude;
    • reversibility;
    • spatial distribution; and
    • equity (who wins and loses).
  • Compare this to the future environmental baseline without the strategic action (and alternatives): this is the magnitude of the impact.


The aim of impact evaluation is to translate the predicted impacts into statements of importance or significance: is the predicted impact worth doing something about or not? Evaluation brings together:

  • the predicted impact (larger magnitude, longer duration etc. = more significant) from the impact prediction stage, and
  • the value and sensitivity of the receiving environment (already stressed, more sensitive etc. = more significant).

The value and sensitivity of the receiving environment can be determined through, for instance,

  • designations like National Parks
  • other measures of value or vulnerability, e.g. how many people use the area or whether any rare species live in the area
  • standards and thresholds: whether standards (e.g. for air quality) are already being exceeded
  • public or stakeholder values: what is important to local residents.

The outcome of evaluation is a yes (significant impact) or no (insignificant impact) statement.


Mitigation aims to maximise positive impacts and (particularly) minimise significant negative impacts. Typical SEA mitigation measures could include:

  • changes to the wording of the strategic action, or components of it
  • the removal of components of the strategic action that are not sustainable or environmentally sound
  • the addition of new components
  • the development of an altogether new strategic action
  • requirements to substitute or offset for certain types of impacts, for instance through projects that replace any benefits lost through other projects
  • requirements and terms of reference for lower-level SEA and/or project environmental impact assessment.

The following is a very basic example of SEA prediction/evaluation (together) and mitigation. 

A real-life objective from a 10-year transport plan for a local authority of approximately 100km x 100km is:

"The aim of the transport strategy for area X is to secure within an available level of expenditure that motorists, those without cars, pedestrians and commercial vehicles are given the maximum freedom of movement and parking compatible with the achievement of convenient and prosperous conditions for all in the area and an acceptable quality of environment."

It looks basically fine, doesn't it?

Now ask yourself some basic questions that would emerge as part of an SEA assessment process:

  • what might this objective look like on the ground?
  • does the objective represent best practice in transport planning? is it consistent with other policies?
  • are environmental concerns well represented in the objective? is it environmentally sound?
  • are all different user groups well represented in the objective? is it equitable?

Below are some of the answers that you might come up with:

These questions should immediately suggest some ways of improving the objective to make it more sustainable, environmentally sound and equitable, for instance:

"The aim of the transport strategy for area X is to ensure that everyone can access jobs and services easily, quickly and safely, whilst minimising environmental harm, in a cost-efficient manner."

There you have it: a basic combined assessment/evaluation (focusing on three questions: environment, equity, current policy) and a series of changes to the objective - mitigation. Smiley

August 31, 2006 Uncategorized — riki @ 9:41 pm

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