Scenario-Based Hazard Trees for Depicting Resolution of Hurricane Uncertainty over Time

Great uncertainty surrounds the future track, intensity, and resulting flooding and wind hazards associated with an offshore hurricane. As time progresses, that uncertainty is reduced, but so is the ability to evacuate or carry out other preparations. A quantitative assessment of how quickly the uncertainty is likely to resolve can thus provide useful input for emergency managers. If the impacts of a hurricane are likely to become more certain soon, an emergency manager may wait for more information. If not, the emergency manager may proceed with preparations. This paper introduces scenario-based hazard trees, a new tool that describes the resolution over time of uncertainty in a hurricane's impacts. The primary input is a scenario ensemble, commonly developed as part of a hurricane forecast. A linear integer program transforms the ensemble into a tree. The hazard trees provide a new dynamic way to characterize how uncertainty changes during the course of a hurricane, and can provide the required input for a multi-stage stochastic programming evacuation model. A case study is presented for eastern North Carolina during Hurricane Isabel in 2003.