Environmental degradation and the depletion of natural resources induced by human activities have attracted steadily growing concerns in the last decades. Such concerns made evident the necessity for the planning authorities to count on sound information about the possible environmental consequences of development actions. One of the tools available to satisfy this need is represented by the procedure of Environmental Impact
Assessment (EIA). This procedure involves the systematic identification and evaluation of the impacts on the environment caused by a proposed project. EIA is now applied worldwide. Its potential role in attaining sustainable development objectives was explicitly recognized during the 1992 Earth Summit held in Rio de Janeiro (United Nations 1992).
Environmental Impact Assessment can be broadly defined as the systematic identification and evaluation of the potential impacts (effects) of proposed projects plans, programmes or legislative actions relative to the physical – chemical, biological, cultural and socioeconomic components of the total environment (Canter, 1996). EIA is a planning tool that is now generally accepted as an integral component of sound decision-making.
Environment may be defined differently depending upon the perspective of the definer. In the case of EIA, environment is usually considered to constitute three main subsystems:
1) Physical Environment (geology, topology, climate, water, air).
2) Biological Environment (terrestrial and aquatic communities, rare and endangered species, sensitive habitats, significant natural sites).
3) Socio-cultural Environment (population, land use, development activities, goods and services, public health, recreation, cultural properties, customs, aspirations).
Impact may be defined as the consequences of changes in the environment but it should not be confused with effect. For example, increase in river pollution due to the initiation of a new project is an effect while a consequence of river pollution on human health, flora, fauna, etc. is the impact.
Assessment normally does not mean doing new science, but rather assembling, summarizing, organizing and interpreting pieces of existing knowledge, and communicating them so that an intelligent but inexpert policymaker will find them relevant and helpful in their deliberations (Munn, 1979).
Environmental Impact Assessment can thus be defined as "the systematic process of identifying future consequences of a current or proposed action (IAIA).” EIA is both an art and a science. Management aspect in EIA is an art, whereas the technical analysis is based on the scientific principles.
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Murthy Aruna, Patra Himansu Sekhar, 2005, Environmental assessment process in India and its drawbacks.