Informational Determinants of Large-area Hurricane Evacuations

This study, published in the Bulletin of the American Meteorological Society, reports on two experiments to investigate the informational determinants of hurricane evacuation decisions (temporal and spatial). Whereas most observational and experimental studies in this domain address the public’s response to forecast information, this study addresses emergency management decisions. Using a subject sample of emergency managers and other public safety leaders, contrasted with a more typical university subject pool, this study presents an experimental design that overcomes the counterfactual problem present in all prior published experiments, by relying on an actual storm (Hurricane Rita) with a known outcome. Several methodological advancements are presented, including the use of an established numeracy instrument, integration of advanced hydrodynamic forecasts, and use of a loss aversion frame to improve generalizability. Results indicate that the availability of additional forecast information (e.g., wind speed, forecast tracks) significantly increases the probability and improves the timing of early voluntary evacuation. However, we observe that more numerate subjects are less likely to avoid relying upon forecast information that is characterized by probability (e.g., the uncertainty in the forecast track, sometimes referred to as the “cone of uncertainty”). Consequently, more numerate emergency managers are almost twice as likely as less numerate ones to provide additional evacuation time to their coastal communities, and they do so by longer than a typical workday (8.8 hours). Results also indicate that subjects knowingly over-evacuate large populations when making spatial mandatory evacuation orders. However, results indicate that numeracy mitigates this effect by more than half in terms of the population subject to mandatory evacuation.