The realities of managing uncertainties surrounding pluvial urban flood risk: An ex post analysis in three European cities

Inner-city pluvial flooding is characterised by major uncertainties, often making response problematic. We explore this in London, Lisbon, and Rotterdam, through ex post document analysis and semi-structured interviews. Traditional uncertainty analysis generally focuses on quantifiable factors, needing to clarify uncertainty for engineering design, flood warnings and incident management. But other uncertainties concern budgets, skills, legal issues, and politics. There are also many relevant certainties or near-certainties, which can dominate. They need equal attention in understanding decision making for risk reduction. Responses to our cities' flood risks-including portfolios of engineering and non-structural measures-also contain significant no-regret components requiring less certainty about risk. Our cities appear to be positioned along a learning continuum, related to flood experience and the consequential uncertainty reduction. However progress can be worryingly slow. Only experiencing actual flood events promotes accelerated action and often the certainties concerning resource constraints also outweigh the many uncertainties in risk assessment.