|Conducting Environmental Impact Assessment in Developing Countries (UNU, 1999, 375 pages)|
|5. EIA tools|
|5.1 Impact prediction|
|5.1.2 Informal modelling|
The "one man prediction'' can be considered as the most informal method of qualitative simulation; a single expert gives their view of the likely effect. From this starting point an increasing formality can be imposed by:
· requiring the "one man'' to justify the opinion by verbal and or mathematical description of the relationships has used, and/or to support the findings by reference to historical and scientific evidence;
· asking "more than one man'', i.e., a group of experts, for their individual opinions and taking some view of their overall conclusions;
· asking a group of experts for their opinion of the likely effect;
· asking the experts to get together in some formal structure for consensus production (e.g., Delhi) and agree on their opinion of the likely effect.
Prediction by analogy is where an effect is predicted by direct extrapolation from a similar activity already operating at another site. The observations from the existing site may be corrected to allow for the different conditions at the site of the proposed activity. In this area, there is an overlap with formal techniques, so empirical models may be developed from an analysis of results from comparable locations.
If the proposed development activity is an addition to an existing situation, a correlation of impact may lead to a prediction. For example, when a resort doubles the number of guest rooms, it will also double the sewage output. The impact on water quality, however, may be much greater if the sewage treatment system is already near its maximum capacity. Trends and correlations may or may not be linear and continuous; thus, extrapolation must be done with care and understanding.
Interpolation may be used to estimate the impact of a new development where the impacts of both larger and smaller similar developments are known. The result is usually more accurate than extrapolation if the assumptions of a linear correlation are true. The analogy between an existing development and a new project allows prediction of impacts depending on the extent of similarity of the sites in both cases. Prediction methods anchored in actual experience are always preferred to estimates with no basis of direct observation.
Comparison with standards is where an effect is predicted to be acceptable by direct evaluation against predetermined standards or norms. This approach is most often used for higher order effects on receptors where environmental standards have been laid down for their protection. For example, the health effects of air pollutants are assessed by comparing air quality with standards for protection of public health.
These informal approaches to prediction are often used together with formal methods in order to qualify and interpret the results.