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Studies by Kockelman (1975, 1976, 1979) on the use of earth-science information by city, county, and regional planners and decision-makers in the San Francisco Bay region of the United States show that the most effective use of hazard information is achieved when maps clearly depict the likelihood of occurrence, location, and severity. If the users do not become proficient in interpreting and applying technical information, the information is likely to be misused or even neglected in the development planning process. Unless the scientific and engineering information is translated for the layman, the effective user community is limited to other scientists and engineers. The effective use of natural hazard information to avoid damage or to reduce loss requires a considerable effort on the part of both the producers and the users of the information. For example, it provides a more equitable basis for allocating disaster planning funds stimulates the use of more efficient, integrated emergency preparedness response and recovery procedures and promotes the creation of cooperative agreements to involve all relevant agencies and interested groups: It must be emphasized that the MHM will not meet the site-specific and hazard-specific needs of project engineering design activities. The adoption of a multiple hazard mitigation strategy also has several implications in emergency preparedness planning. It becomes a comprehensive analytical tool for assessing vulnerability and risk, especially when combined with the mapping of critical facilities as discussed in Chapter 7. The MHM is an excellent tool to create an awareness in mitigating multiple hazards. Characteristics of the natural phenomenon and its trigger mechanisms are synthesized from different sources and placed on a single map.Īdditionally, the effects and impact of a single hazard event, as in the case of volcanoes and earthquakes, include different types of impacts, each having different severities and each affecting different locations. The inducing or triggering mechanism which can interconnect several hazards can more easily be seen through the use of a MHM. Many natural hazards can be caused by the same natural event. Using individual maps to convey information on each hazard can be cumbersome and confusing for planners and decision-makers because of their number and their possible differences in area covered, scales, and detail. (Figure 6-1 is a tabulation of natural phenomena that can be considered for presentation on such maps). One area may suffer the presence of a number of natural hazards. A MHM may also be referred to as a "composite," "synthesized," and "overlay" hazard map. The main purpose of MHM is to gather together in one map the different hazard-related information for a study area to convey a composite picture of the natural hazards of varying magnitude, frequency, and area of effect. In this chapter, the MHM discussed is primarily for use in an integrated development planning study. In either the planning of new development projects or the incorporation of hazard reduction techniques into existing developments, the MHM can play a role of great value. By facilitating the interpretation of hazard information, it increases the likelihood that the information will be used in the decision-making process. When an area is exposed to more than one hazard, a multiple hazard map (MHM) helps the planning team to analyze all of them for vulnerability and risk. This chapter presents the concept of multiple hazard mapping, describes the benefits of using multiple hazard maps relative to individual hazard maps, and explains the preparation and use of such maps.