Tsunamis are among the world’s most destructive and fatal coastal hazards. Triggered by the Dec. 26, 2004, undersea earthquake off Sumatra, the greatest tsunami in memory caused the tragic death of an estimated 230,000 people in the Indian Ocean region. The tragedy demonstrated the urgent need for early warning systems not only for regions near the Indian Ocean, but also globally as the tsunami hazard exists in all oceans and seas.

Following the 2004 tsunami, the U.N. Educational, Scientific, and Cultural Organization’s Intergovernmental Ocean-ographic Commission (UNESCO IOC) led immediate efforts to establish an Indian Ocean warning system, and an interim system has been in place in the region since April 2005, as well as in the South China Sea and the Caribbean since this year. Permanent coverage for the Gulf Coast of Mexico and East Coast of North America began at the end of last year. These systems extend the alert system beyond the Pacific, where an international tsunami warning system has been operating since 1965. Despite this progress, however, much work is ahead before the coastal communities of the world can be truly prepared.

Tsunamis are low frequency, high impact natural disasters that are also unpredictable: We may not see another destructive tsunami in 100 years or we may see another one tomorrow. These characteristics pose a unique set of challenges for hazards mitigation, including, first and foremost, preparation.

An effective tsunami early warning system is achieved when all people in vulnerable coastal communities are prepared to respond appropriately and in a timely manner upon recognizing that a potential destructive tsunami may be approaching. Facing this challenge will require round-the-clock monitoring with real-time data streams and rapid alert dissemination, as well as prepared communities, a strong national disaster management system, and close and effective cooperation and coordination between all stakeholders.

At the core of the early warning system is the National Tsunami Warning Center (NTWC), which is the 24/7 focal point for receiving timely reports from international centers worldwide. Additionally, for countries with a local tsunami threat, such as Japan, Indonesia, Chile and parts of the eastern Mediterranean, the NTWC must have a local warning system with denser instrument networks so that they can evaluate and provide a warning within minutes of an earthquake. These centers must be fully interlinked with the national disaster management organization, which will receive the NTWC warnings and then take immediate action to warn communities of imminent danger.

To warn without preparing, and further, to warn without providing a public safety message that is understandable to every person about what to do and where to go, is clearly useless. While alerts are the technical trigger for early warning, any system will ultimately be judged by its ability to save lives, and by whether people move out of harm’s way before a big tsunami hits.

That lesson hit home on July 17, when a local tsunami struck Indonesia 21 minutes after an earthquake, resulting in more than 400 deaths on the island of Java. Although the Indonesia earthquake monitoring center had information indicating a potential tsunami threat, the mechanisms for alerting coastal authorities — along with enacting the community’s plans and procedures for tsunami emergency response and evacuation — were not in place. Thus, we learned again that for local tsunamis where a wave can strike in minutes, technical warning systems are not enough, and that public education and awareness at the community level are most urgent and essential.

In the aftermath of the July tsunami, much has happened. Indonesia’s tsunami alert communications systems have been enabled through the police and media, and many districts and provinces are developing emergency plans and conducting tsunami drills to prepare themselves for the next local tsunami.

To date, 26 of the 29 countries around the Indian Ocean have designated official receiving points for advisory alerts. Upon receiving the alerts, each country is then responsible for evaluating the regional threat and providing the relevant public safety advice to their people and any vulnerable coastlines. As we know, a tsunami’s impact upon a particular coastline is dependent on local seafloor conditions and the character of the coastline, and therefore is best evaluated and acted upon by national and local authorities.

Between April 2005 and August 2006, these alerts have been issued 13 times, on average between 16 and 21 minutes after the earthquakes, using regional real-time seismic data primarily from the Global Seismic Network, which is managed by the Incorporated Research Institution for Seismology and the U.S. Geological Survey. For the earliest of tsunami warnings, we rely on the monitoring of earthquakes because more than 70 percent of tsunamis are caused directly by tectonic earthquakes, and another 20 percent by landslides or volcano processes for which seismic monitoring can provide early detection. This, together with the known fact that seismic waves travel more than 40 times faster than tsunami waves, allows warning and emergency operations centers to issue alerts and evacuations before a tsunami wave arrives.

Over the past year, IOC has led an effort, supported by contributions from a number of sources, to upgrade sea-level monitoring stations of the Global Sea Level Observing System to transmit more frequently, to provide faster confirmation on whether a tsunami has been generated. By this month, 25 sea-level stations will report every 15 minutes by satellite, whereas in 2004, 11 were reporting only hourly, and none transmitted to the tsunami warning centers.

The next step is for countries to work together to focus on national and local tsunami emergency response and preparations, so that every citizen, whether young or old, knows what a tsunami is, how to recognize one and what to do to save their lives. It is not an easy effort, and it will take time, but each small step forward will hopefully build the preparedness for our future generations.

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