Warning

On the Effectiveness of Warnings

Various factors influence the effectiveness of warnings. The first is the predictability of the hazard.

Imprecise Predictions

The problem of imprecise predictions is compounded by other factors that influence the effectiveness of warnings. Precise prediction is difficult or impossible if there are no precursors, or if these are unclear or indeterminate. Likewise, the speed of onset will determine the window of time available to assess the situation and issue a warning. The frequency, duration, and size of the impact are also relevant factors, as is the degree to which it can be limited or controlled by timely action. Nevertheless, a clear situation of identifiable precursors that have a known sequence and predictable timing would provide a good basis for launching the warning process. Floods, snow avalanches, hurricanes, and storms often show promise in this respect. Despite a long, drawn-out search for reliable precursors, earthquakes are largely unpredictable in the short term (although general seismicity is known and predicted). Through enhanced heat flux and surface deformation, volcanoes offer a good basis for predicting that an eruption is imminent, but it remains difficult to pin down the exact timing of its onset or how long it will last.

Anatomy of a Warning System

In synthesis, a warning system should consist of technical and social components, monitoring and evaluation procedures, technology and organization, planning, and communication. The absence of any of these ingredients is likely to compromise the effectiveness of the whole system.

There are several stages in the implementation of the warning process. To begin with, decision makers who are responsible for public safety must recognize that a warning is needed and that it is feasible. They must then decide whom to warn, about what, and by what means. A system must be designed, installed, and tested. It must be able to receive reliable information from the monitoring of a hazard with sufficient time to convert it into a warning message and disseminate this to [Page 992]users; for example, the general public in a given area, or a specific subset of the public, such as disabled people. A warning message should state the

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