How scale affects environmental impact assessment

This paper evaluates the influence of geographical scale on the outcomes of Environmental Impact Assessments (EIAs). The paper presents results obtained by using spatial data with different scales for an EIA for a proposed road bypass in Southeast England (the Hastings Bypass). Scale effects were measured separately for spatial extent and spatial detail, and were measured both quantitatively using a Geographical Information System (GIS) and qualitatively using the judgement of EIA experts. The study found that changes in scale could affect the results of EIAs. For example, the impact significance and the number of houses affected by air pollution from the road varied according to the scale used. These observed scale-dependent changes suggest that scale choice can have important repercussions for the accuracy of an EIA study. This situation is made more serious when it is recognized that many environmental impact statements (EIS) fail to mention in explicit terms the scale used. The paper concludes with recommendations for future practice on how best to control the quality of EIAs in relation to scale choice.