Forward propagation of uncertainty within board-scale national flood risk models

Over the past twenty years risk based analysis has become come place in support of flood management decisions. In more recent times it has been increasingly recognised that board-scale analysis of risk is a necessary pre-requisite to effective and efficient policy planning, aiding the prioritisation of medium to long term investment at regional or national scale. The so-called RASP models (Risk assessment for strategic planning) provided a structured analysis of the flood risk system and have been used to estimate the national exposure to flood risk within England and Wales annually since 2002. This paper will explore the quantification of uncertainty in the outputs from such broader scale models taking account of model structure and parameter uncertainties. The approach described uses a combination of structure sensitivity and uncertainty analysis - using hierarchical statistical techniques – practical validation techniques and expert judgement enable important uncertainties to be highlighted. The paper also describes the communication of the uncertainty in the national estimates of flood risk at a national and local level based on the board scale models.