“Ripe for decision”: Tiering in environmental assessment

Tiering of information and decisions from more strategic plans to more specific projects (and sometimes the other way) can streamline plan-making and assessments, and improve decisions at each planning tier. In particular, it can lead to more consistent and comprehensive impact mitigation at the lower tiers. In practice, however, tiering of assessments is carried out only sporadically. This paper reviews the international literature and case studies on Strategic Environmental Assessment (SEA) and Environmental Impact Assessment (EIA) tiering, and presents the findings of interviews with 14 SEA/EIA experts. It concludes that a conscious and explicit transfer of information from the SEA level, and an explicit receipt of this information at the EIA level are necessary prerequisites for effective tiering. SEAs must be carried out with local actions in mind, in order for mitigation measures to support environmental protection on the ground. Lower-tier decision-makers must also be willing to be bound by decisions by the higher-tier SEA, focusing on implementation of these decisions.