The special issue on “Community-based last-mile early warning system” carried on its back page the following contribution from Rohan Samarajiva (despite the title of the publication, it’s not possible to find this piece on the web, so what is pasted below is the pre-pub version:
Between a rock and a hard place
The tragedy of the 2004 Indian Ocean tsunami was the absence of any official warning. The Bengkulu earthquake of 2007 September 12th shows that this is unlikely to be repeated. What we must guard against now is indifference to warning; of populations that will refuse to evacuate in the face of real danger.
Tsunami prediction is an inexact art practiced in conditions of imperfect information and time pressure. In the Pacific Basin, which has had the most experience with tsunamis, 75 per cent of all warnings are false. But this causes little harm because the false warnings do not get through to the general population for the most part.
Tsunamis are short-fuse hazards. It took 90 minutes for the 2004 India Ocean tsunami to reach the South-eastern coast of Sri Lanka. In September 2007, the earthquake occurred at 1110 UTC or 4:40 PM Sri Lanka time. Tsunami Bulletin 001 issued by the Pacific Tsunami Warning Center at 1124 UTC (4: 54 PM Sri Lanka time) projected arrival times of over three hours.
Time must be allocated to decision making at the national level about issuance of watch, warning or evacuation messages; and decision making and action at community level, including evacuation if appropriate. This means that the time taken to communicate the watch/warning/evacuation messages must be minimized.
This does not mean, however, that evacuation orders should be given as quickly as possible. False evacuation orders will reduce public response over time.
Given the massive costs associated with evacuation orders (not only in lost productivity but deaths, injuries and other negative outcomes), government must be the sole authority. Given the certainty of blame if a tsunami does hit, over-use of warnings and evacuation orders is likely. It is important that procedures be established not only to make considered but quick decisions about watch/warning/evacuation messages, but also to counter the bias toward excessive warnings and evacuation orders.
Disaster risk-reduction professionals know that false warnings are an artefact of the inexact art of predicting the onset of hazards: but the general public does not. If they are subject to too many false warnings, they will not respond even to true warnings.
Now that we have gotten over the problem of issuing no warnings, we have to address the problem of false warnings.
Rohan Samarajiva, Ph.D.
Project Director, Last Mile HazInfo Project &
Executive Director, LIRNEasia
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