Mitigating natural disasters through collective action: the effectiveness of tsunami early warnings.

• Author: Escaleras, Monica P.

1. Introduction

   While not the most prevalent of all the natural disasters plaguing humankind, tsunamis have proven more devastating in their potential than any of the others. Tsunamis occur for a variety of reasons, including landslides and submarine volcanic and seismic activity, though by far the most common cause is the latter. This type of tsunami may be generated any time tectonic plates scrub together beneath a body of water severely enough to cause one plate to drive beneath another, a process known as subduction. When this occurs, the seabed buckles, thrusting a column of water upward. Once the column reaches the surface, this mass of water or set of waves races at speeds sometimes in excess of 700 km/h, potentially devastating any adjacent land areas.

   [FIGURE 1 OMITTED]

   Because Earth's surface is made up of constantly shifting tectonic plates, an earthquake-generated tsunami may occur almost anywhere there is a large mass of water. While potentially striking all of the world's oceans and seas, tsunamis are most common in the Pacific basin; although, the rapid development of coastal areas of the past decades has increased the devastating potential of tsunamis, these great waves and humankind share a long history. Our earliest evidence of a tsunami shows that one occurred in the Aegean Sea in 1480 BC from the volcanic explosion on the island of Santorini, which effectively wiped out the thriving Minoan civilization on the island of Crete. More recently, since 1966 alone, there have been 202 tsunamis worldwide (see Figure 1, which identifies the primary area, known as the tsunami's run-up, where each of these events had its greatest impact). The worst of these was caused by the megathrust earthquake that struck the Indian Ocean on December 26, 2004, the epicenter of which was only about 30 km from the shores of the densely populated Indonesian island of Sumatra. The subduction of the oceanic India-Australia tectonic plate beneath the Burma subplate of the continental Eurasia plate caused the seabed to suddenly and violently rise by some 10 m, generating the series of waves that claimed the lives of about 150,000 individuals in Indonesia alone and as many as 290,000 individuals in total.

   Given the widespread nature and destructive potential of tsunamis, it is surprising that much of the world lacks even the most rudimentary of tsunami warning systems, especially because such systems are not particularly expensive to establish and have been in place in the Pacific for more than 50 years, (1) Of the many potential explanations for the lack of global coverage, two are interrelated and most closely tied to the present study and deal with the collective good nature of warning systems and their effectiveness. One might reasonably question whether the limited coverage is due to the common collective-good problem of free-riding. That is, in the absence of the international cooperation necessary to minimize or eliminate the incentive for countries to take advantage of warnings issued by others without having to bear the costs of creating and operating warning systems such free-riding would seem predictable. (2) The early history of the warnings systems in the Pacific may point to the free-rider problem in that prior to 1965 most countries in that area could benefit from Pacific-wide warnings issued by the national tsunami warning centers operated until that time by the United States, Japan, and the Soviet Union. Unfortunately, data on warnings issued prior to the mid-1960s are not available, thus we can only offer this as a possible explanation for the limited international cooperation in the Pacific basin prior to that time. At a minimum, however, only three of the wealthiest countries in the region operated warning systems in the early period, which is consistent with the existence of a free-rider problem. Since 1965, however, the free-rider issue in the Pacific has become a moot point: These national systems became international in nature through the creation of the United Nations Educational, Scientific and Cultural Organization's (UNESCO's) 26-member International Coordinating Group for the tsunami warning systems covering the entire Pacific basin, as is discussed later.

   Contrary to the situation for countries within the Pacific basin prior to 1965, international free-riding by countries outside that basin on the Pacific systems' warnings has never been much of a possibility. The reason for this is simply that the Pacific's various warning systems, prior to 2006, lacked the technology and equipment necessary to accurately sense the formation of tsunamis outside the Pacific basin. Of course, while countries outside the Pacific could not free-ride on the Pacific systems' warnings, the possibility of free-riding may help explain why warning systems have not come into being outside the Pacific basin. To the extent that this problem exists, international coordination of the type put in place in the Pacific by UNESCO in the mid-1960s would likely prove effective. We return to this point in the paper's conclusion.

   A second potential explanation for the poor coverage outside the Pacific basin may simply be that these warning systems are of limited effectiveness. This question is the focus of the current paper. Specifically, the purpose of this paper is to assess the effectiveness of tsunami early warning systems in terms of lives saved. To do so, we analyze 146 of the 202 tsunamis occurring worldwide between 1966 and the end of 2004. Controlling for the dynamics of the tsunami and socioeconomic factors of the affected areas, as well as other relevant factors, we find that when tsunamis are accompanied by warnings, there is a statistically significant reduction in deaths. In the following section, we offer an overview of prior research with respect to the mitigation of natural hazards and give a brief history of the warning systems in the Pacific, along with a description of how these systems operate. We then describe the data, empirical methods, and results for our primary models. Next, to provide some idea of the stability of the results of the primary models, we offer results from a number of alternatives to those models, followed by a summary conclusion.

2. Natural Hazard Mitigation and the Tsunami Early Warning System

   Tsunamis are one example of a lengthy list of natural hazards confronting humankind. A nonexhaustive list would include earthquakes, floods, tornadoes, avalanches, landslides, mudslides, and hurricanes. The potentially disastrous effect of each is subject, to one degree or another, to human mitigation. A growing body of literature addresses the effectiveness of mitigation efforts. For example, Simmons and Sutter (2005) identify a significant decline in fatalities from major tornadoes in the United States during the last century, controlling for factors like increasing population densities and income levels. More broadly, Sudo, Kameda, and Ogawa (2000) consider the Japanese government's aggressive attempts to mitigate various natural hazards since the 1940s through such programs as early warning systems. They note that while natural hazards of all types claimed an annual average of 1941 lives in the 1950s, that number fell to just 200 in the 1980s, a downward trend that has continued, with the exception of the massive Kobe earthquake in 1995. Good general surveys of the recent progress made with respect to early warning systems can be found in Mileti (1999) and Sorensen (2000). (3) However, a rigorous analysis of the effectiveness of tsunami warnings has never been presented.

   Before we offer our analysis, insight can be had by considering the evolution of the existing tsunami warning system in the Pacific. One of the most destructive tsunamis of the past century resulted from a great earthquake centered near Unimak Island in Alaska's Prince William Sound on April 1, 1946. (4) This event lead to the deaths of 165 people from Alaska to Hawaii and marked a tipping point with respect to the commitment of the United States to develop a warning system for tsunamis in the Pacific. As is often the case, particularly severe examples of recurring disasters can galvanize policy makers to undertake mitigating actions, such as creating early warning systems to reduce the damage done by similar future events. The first steps in this direction were taken in 1947 and 1948 by scientists working within various federal agencies, most notably the U.S. Coast and Geodetic Survey, with the establishment of the Pacific Tsunami Warning Center (PTWC) headquartered in Honolulu. The system was composed of two parts: a set of three seismological observatories and nine coastal tide stations distributed throughout the Pacific. The PTWC was charged with providing early warnings of tsunamis that might affect Hawaii or any of the islands making up the U.S. Trust Territories of the Pacific. By 1953, this charge was extended to include the provision of early warnings to the west coast of the continental United States.

   A second tsunami warning center, the West Coast/Alaska Tsunami Warning Center based in Palmer, Alaska, was soon added to complete U.S. coverage of the Pacific. Other countries--most notably Japan, the Soviet Union, and Chile--quickly developed their own national warning centers. Following the great earthquake of March 28, 1964, centered in the Gulf of Alaska, which killed 120 individuals, what had been examples of national collective action became international in nature when, in 1965, the existing national warning centers were brought together to form an international warning center, the Tsunami Warning System in the Pacific (TWSP), hosted by the United States at its PTWC in Honolulu. At the same time, the International Tsunami Information Center was established by the UNESCO Intergovernmental Oceanographic Commission to monitor the effectiveness of the TWSP and to facilitate technology transfer to...