/ 05 Public Evacuation Decisions and Hurricane Track Uncertainty

Public officials with the authority to order hurricane evacuations face a difficult trade-off between risks to life and costly false alarms. The evacuation decision must be made on the basis of imperfect information, in the form of a forecast. Ideally, the decision should also be informed by measures of uncertainty and estimates of the value of waiting for updated, and more accurate, forecasts. Using a stochastic model of storm motion derived from historical tracks, this paper explores the relationship between lead time and track uncertainty for Atlantic hurricanes, and the implications for evacuation decisions and false alarm costs. Typical evacuation clearance times and forecast uncertainty imply that public officials requiring a 10% probability of failing to evacuate before a striking hurricane (a false negative) must accept that at least 75%, and for some locations over 90%, of evacuations will be false alarms. Reducing the decision lead time from 72 to 48 hours for major population centers could save on the order of $1B in evacuation costs annually. The savings differ by geographic location: for example, reducing the evacuation decision lead time from 72 to 48 hours lowers the false alarm rate from 76 to 69% at Miami, but only from 82 to 81% at New Orleans. At all lead times, New Orleans and Eastern Long Island would need to accept a higher rate of false alarm evacuations than Miami to achieve the same probability of a false negative.