Impact prediction, evaluation and mitigation - Introduction to Environmental Impact Assessment - page 131

5
Impact prediction, evaluation and
mitigation
5.1 Introduction
The focus of this chapter is the central steps of impact prediction, evaluation and
mitigation. This is the heart of the EIA process, although, as we have already noted, the
process is not linear. Indeed the whole EIA exercise is about prediction. It is needed at
the earliest stages, when a project, including its alternatives, is being planned and
designed, and it continues through to mitigation, monitoring and auditing. Yet, despite
the centrality of prediction in EIA, there is a tendency for many studies to
underemphasize it at the expense of more descriptive studies. Prediction is often not
treated as an explicit stage in the process; clearly defined models are often missing from
studies. Even when used, models are not detailed, and there is little discussion of
limitations. Section 5.2 examines the dimensions of prediction (what to predict), the
methods and models used in prediction (how to predict) and the limitations implicit in
such exercises (living with uncertainty).
Evaluation follows from prediction and involves an assessment of the relative
significance of the impacts. Methods range from the simple to the complex, from the
intuitive to the analytical, from qualitative to quantitative, from formal to informal. CBA,
monetary valuation techniques and multi-criteria/multi-attribute methods, with their
scoring and weighting systems, provide a number of ways into the evaluation issue. The
chapter concludes with a discussion of approaches to the mitigation of significant adverse
effects. This may involve measures to avoid, reduce, remedy or compensate for the
various impacts associated with projects.
5.2 Prediction
5.2.1 Dimensions of prediction (what to predict)
The object of prediction is to identify the magnitude and other dimensions of identified
change in the environment with a project or action, in comparison with the situation
without that project or action. Predictions also provide the basis for the assessment of
significance, which we discuss in Section 5.3.