Cover Image
close this bookConducting Environmental Impact Assessment in Developing Countries (UNU, 1999, 375 pages)
close this folder9. Emerging developments in EIA
close this folder9.2 Cumulative effects assessment
close this folder9.2.2 Conceptual framework
View the document(introduction...)
View the document9.2.2.1 Sources of cumulative environmental change
View the document9.2.2.2 Pathways of cumulative environmental change
View the document9.2.2.3 Cumulative effects

9.2.2.1 Sources of cumulative environmental change

A typology to describe and classify various sources of cumulative environmental change is shown in Table 9.2. The typology differentiates sources according to temporal, spatial, and perturbation attributes. Three examples illustrate various ways in which the typology can be applied to different sources. Construction of a hydroelectric dam is typically viewed as a single, discontinuous event at the local scale. However, dam construction is a potential source of cumulative effects when characterized by multiple perturbations of the same type (e.g., several hydroelectric projects) or different type (e.g., access roads, transmission corridors), expanded spatial scales (e.g., loss of upstream terrestrial habitat as the impoundment fills, altered downstream flow), and extended temporal bounds (e.g., eventual release of methyl mercury and the gradual deposition of sediment in the reservoir).

It could also be argued that clear-cutting of a forest is a single, discontinuous event at the local scale. However, once a particular stand of trees is cut, the operators move elsewhere. Clear-cutting is a potential source of cumulative effects because the action is repeated over time and across space (see Table 9.2).

Finally, CO2 emissions are also representative of cumulative effects. The increasing accumulation of CO2 in the atmosphere has occurred over the long term (i.e., since the pre-industrial era) and at a global scale. CO2 emissions come from diverse and multiple sources (e.g., thermal power plants, transportation, heating) (see Table 9.2).

This typology broadens the consideration of sources (i.e., human actions) beyond the bounded projects typically appraised by environmental assessments to include activities which are repeated over time and dispersed across space.