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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
View the document(introduction...)
Open this folder and view contents9.2.1 Concepts and principles relevant to CEA
Open this folder and view contents9.2.2 Conceptual framework
View the document9.2.3 Conclusion

9.2.3 Conclusion

Cumulative environmental problems can be desegregated by distinguishing their sources, pathways, and effects. Application of the typology specific to each component provides a basis for identifying and analysing perturbations, mechanisms of accumulation, and temporally and spatially differentiated effects. The framework can provide guidance to conventional CEA practice characterized by multiple projects bound in time and space, as well as to innovative CEAs of temporally repetitive and spatially dispersed human actions of a non-project nature. Such CEAs can generate new information and insights about environmental changes too frequently deemed insignificant.

Table 9.4 Characterizing cumulative effects




Action quantity

Single, multiple, global, cause unknown

Action type

Similar or different, common or uncommon, human or natural, additions to or removal from environment

Temporal characteristics

Historical, existing, or future; short, medium, or long term; low, moderate, or high frequency; continuity of actions over time

Spatial characteristics

Local, regional or global; small or large scale; continuity of actions over space


Single or multiple; public or private

Source connections

Connected, unconnected, uncertain connections

Pathways to the environment

Environmental media

Groundwater, surface water, air, energy

Degree of concentration

Concentrated or dispersed over time and space

Degree of continuity

Continuous or discontinuous over time or space (e.g., time or space lags)

Pathway connections

Connected pathways, unconnected pathways, uncertain connections across pathways


System type

Number, type, components, structure, and function of ecological, social, economic, institutional and political systems


Number, type and significance


Number and type of valuable ecosystem and other ecological components

State of environment

Healthy, impaired, or collapsed; stable or unstable; resilient or not resilient

Environmental connections

Connected components, unconnected components, uncertain connections


Connection to sources

Connected, not connected, connections uncertain

Strength of connections

Strongly connected, weakly connected

Direction of connection

Direct, indirect, feedback

Temporal distribution

Concentrated or dispersed; continuous or discontinuous distribution of effects

Special distribution

Concentrated or dispersed; continuous or discontinuous distribution of effects

Nature of connections

Additive or interactive, reversible or irreversible

Significance of connections

Significant, insignificant, uncertain significance

There remain challenges to conduct a CEA focused on sources, pathways, and effects. Sources of cumulative environmental change that are non-project in nature are likely to involve numerous "proponents'', if they can even be identified.

The least understood of the three components of the framework is pathways of accumulation. The complexity of these pathways is evident in multiple routes, feedback loops, and processes that are interactive, synergistic, or involve compounding. Theoretical understanding and tools to identify, monitor, and analyse these pathways are not readily available.

Finally, while cumulative effects can be analysed using available information sources, empirical evidence is often scanty, and quantitative analyses of effects are hindered by insufficient data. CEA requires a temporal scan of long duration and geographic representation at various scales. The limited time span and local focus of many existing databases impede analyses at broader temporal and spatial scales. Rigorous analysis of cumulative effects requires building up the empirical base.

The field of CEA is still in its infancy, so there are few cases where CEAs for major projects have been completed. In general, thus, there is more agreement on the concept of CEA than there is on practical methodologies and techniques.