Accounting for Joined Probabilities in Nation-Wide Flood Risk Profiles

A risk profile provides information about the probabilities of event impacts of varying magnitudes. In this study, a probabilistic framework is developed to derive a national-scale flood risk profile, which can be used for disaster risk management and financial planning. These applications typically require risk profiles over a wide range of return periods. For most countries, the historical record of flood impacts is limited to a few decades, insufficient to cover the longest return periods. To overcome this limitation, we developed a stochastic model that can generate arbitrarily long synthetic time series of flood events which have the same statistical characteristics as the historical time series. This includes the joint occurrence probabilities of flood events at different locations across the country. So, the probability of each pair of locations experiencing a flood event in the same event should be the same for the synthetic series as for the historic series. To this end, a novel approach based on ‘simulated annealing’ was implemented. Results show an almost exact reproduction of the statistical properties of the historical time series.