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CHAPTER 2 Reducing the Impacts of Natural Hazards RAPID-ONSET AND LONG-TERM HAZARDS The natural hazards emphasized in this report- floods, landslides, earthquakes, tsunamis, hur- ricanes, tornadoes, volcanic eruptions, and wild- fires - share many characteristics. All are rela- tively sudden and are of short duration. Their occurrence is easily identified geographically. They occur frequently enough, globally, that we now have a large body of data on them and considerable experience in alleviating their effects. And we can reduce their impacts with a common set of skills, including immediate warn- ings, construction techniques, land use planning, and emergency relief. In many countries, knowl- edgeable scientists, engineers, and others are prepared to help in this mitigation effort. The effects of many long-term natural hazards - drought, insect plagues, and desertification, for example - can also be mitigated. These hazards can be just as devastating as rapid-onset hazards, but dealing with them calls for a somewhat different set of skills. Generally, mitigating these hazards requires a greater ecological or social emphasis, and civil engineering approaches are less critical than for short-duration hazards. Fur- ther, the accumulation of knowledge, trained professionals, and public awareness already con- centrated on rapid-onset hazards means that continued work on them during the Decade will yield the most tangible and immediate benefits, given the limited resources available. Thus, while not excluding long-ternl hazards, the initial focus of the IDNHR should be the eight hazards listed above. Of course, many of the activities designed to cope with rapid-onset hazards will also lessen the risks of long-term hazards. For instance, a better understanding of meteorological processes in- volved in storm hazards may benefit our under- standing of drought as well. In addition, other efforts, such as the proposed International Geophysical Year (IGY) and the International Biosphere-Geosphere Program (IGBP), should measurably improve our understanding of the ecological basis of many long-term hazards. Technological hazards, although of great im- portance, are not considered in this report. They are characterized by opportunities for human control- both political and technological- that are not available for natural hazards. A WORLD AT RISK Virtually all parts of the world are at risk from the inevitable occurrence of one or more types of natural hazards. Each year, hundreds of poten- tially damaging earthquakes (magnitude 6 or greater) occur. Those that are located sufficiently near a city precipitate disasters. Most earthquakes occur at the margins of major tectonic plates. The highest percentage of the total seismic energy released in earthquakes is distributed along the "ring of fire," which marks the boundary of the Pacific plate. It is also the zone at greatest risk from tsunamis and volcanic eruptions. Although 9