Plain-language explanation.
Environmental impact assessment (EIA) is a process that evaluates the likely environmental effects of a proposed development — like a new road, factory, or housing estate — before it is approved. It helps decision-makers understand trade-offs and require measures to reduce harmful impacts. EIA is required by law in most countries.
Core concepts and standard treatment.
EIA process stages: screening (is EIA required?), scoping (which issues to assess?), baseline data collection, impact prediction and evaluation, mitigation hierarchy (avoid, minimise, restore, offset), reporting (Environmental Impact Statement), review and decision, and post-approval monitoring. Strategic environmental assessment (SEA) applies impact assessment to policies, plans, and programmes upstream of project-level EIA.
Deeper theory, debates and edge cases.
Cumulative impact assessment considers how a project's impacts combine with those of other past, present, and foreseeable projects. Social impact assessment (SIA) addresses impacts on community wellbeing, livelihoods, and cultural heritage, with Free, Prior and Informed Consent (FPIC) requirements for projects affecting indigenous peoples. Health impact assessment (HIA) quantifies effects on human health — an emerging integration with EIA.
How it is applied in practice.
EIA practice faces persistent quality challenges: over-optimistic baseline characterisation, prediction uncertainty obscured by false precision, and ineffective post-approval monitoring. Digital EIA tools — GIS-based impact mapping, noise and air dispersion modelling, visualisation for public participation — are improving assessment quality. EIA for infrastructure in climate-vulnerable settings must now assess climate risk to the project (physical risk) alongside project impacts on climate (mitigation risk) — a significant methodological extension.