Flood adaptation decision-making for vulnerable locations using expectation–quantile–investment analysis

Floods represent one of the major challenges facing human societies. The impacts caused by them are extensive, and efficient flood adaptation will playa key role in the current century. The present work proposes a new approach to decision-making in flood adaptation aimed at achieving robust adaptation decisions. It consists in evaluating decisions on a triaxial basis that considers expectation, probability quantile and investment in a so-called expectation–quantile–investment (EQI) evaluation. With such approach it is possible to understand the influence of uncertainties in the probabilistic response of adaptation. While adaptation should minimise expected total costs, it needs also to be robust for competitive levels of investment. Transfer curves that relate events with outcomes are used to infer on the probabilistic character of decisions in a case study of a vulnerable location. Results show that EQI-informed decisions can distinguish optimality in apparently competitive measures. It is shown that decisions based on one-dimensional or two-dimensional aspects of this triaxial rationale may fail to identify important probabilistic outcomes of adaptation, such as, the possibility of large losses with relevant probability of occurrence; and that are of high relevance when uncertainty considerations need to be enclosed in the analysis of adaptation.