Imagine – Scenario Development for Environmental Impact Assessment Studies

Scenario analysis is a process of evaluating possible future events through the consideration of alternative possible (though not equally likely) outcomes (scenarios). The analysis is designed to enable improved decision-making and assessment through a more complete consideration of possible outcomes and their implications. The development of strategies for water resources planning and management and the assessment of impacts of potential environmental change are often guided by analyzing multiple future scenarios within an Integrated Modeling (IM) framework, usually driven by forcing derived from global climate models and/or possible future socio-economic changes. The process of scenario development involves making explicit and/or implicit assumptions about potential future conditions, such as climate change, land cover and land use changes (e.g. urbanization), population growth, economic development, and technological change. These scenarios generally surpass forcing or behavior that has been observed in the past. Realistic assessment of scenario impacts requires complex modeling frameworks that represent environmental and socio-economic systems to the best of our knowledge, including assumptions about probabilities of the occurrence of future conditions. In addition, scenarios have to be developed in a context relevant to the stakeholders involved, to facilitate transparency of scenario results, and to establish credibility and relevance of the results among them. Hence, for the IA models to be useful for policy making, appropriate scenarios have to be carefully constructed and associated uncertainties propagated into the model outputs have to be understood and quantified. This paper is a review of the state-of-the-art of scenario development.