Ex-post impact assessment on a large environmental disaster

Impact assessments following environmental disasters must be quick and in accessible language so that decision-makers and affected populations are aware of the main impacts and can target recovery measures. After the collapse of the Fundão dam (Minas Gerais, Brazil) in November 2015, an extensive monitoring program was implemented to understand the aquatic environmental situation and associated biodiversity status after the spill of the iron ore tailings in a large and highly populated watershed, that reached the Atlantic Ocean along the southeast Brazilian coast. A monitoring programme faced several challenges, including the large volume of data to be analysed, which difficult an objective environmental diagnosis and the communication between technical teams and decision makers. In this context, an impact matrix was proposed as a tool for assessing the environmental proxy results and summarizing the results obtained. The proposed Impact Matrix is an interaction matrix adaptation which consists of quantifying the impacts using pre-defined criteria and scores. Expert panels assessed the link between environmental measures and objectives by scoring the specific criteria. As an interaction matrix, the impact matrix is made up of two intersecting axes: the identified impact and the affected environmental compartments (whether abiotic or biotic). The final impact matrix is reached by summing up the score for the criteria on each of the identified intersections. The impact matrix is a supervised approach focused on provide relatively simple tool to apply and, when carried out periodically in parallel with a monitoring programme, it makes it possible to observe temporal trends in the evolution of the environment after the event causing the impact. The impact matrix can also serve as feedback to the monitoring programme itself, when used in an adaptive management approach.