Hazard, vulnerability, and risk analysis

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This chapter describes how preimpact conditions act together with event-specific conditions to produce a disaster’s physical and social impacts. These disaster impacts can be reduced by emergency management interventions. In addition, this chapter discusses how emergency managers can assess the preimpact conditions that produce disaster vulnerability within their communities. The chapter concludes with a discussion of vulnerability dynamics and methods for disseminating hazard/vulnerability data.


A disaster occurs when an extreme event exceeds a community’s ability to cope with that event. Understanding the process by which natural disasters produce community impacts is important for four reasons. First, information from this process is needed to identify the preimpact conditions that make communities vulnerable to disaster impacts. Second, information about the disaster impact process can be used to identify specific segments of each community that will be affected disproportionately (e.g., low income households, ethnic minorities, or specific types of businesses). Third, information about the disaster impact process can be used to identify the event-specific conditions that determine the level of disaster impact. Fourth, an understanding of disaster impact process allows planners to identify suitable emergency management interventions. The process by which disasters produce community impacts can be explained in terms of models proposed by Cutter (1996) and Lindell and Prater (2003). Specifically, Figure 6-1 indicates the effects of a disaster are determined by three preimpact conditions—hazard exposure, physical vulnerability, and social vulnerability. There also are three event-specific conditions, hazard event characteristics, improvised disaster responses, and improvised disaster recovery. Two of the event-specific conditions, hazard event characteristics and improvised disaster responses, combine with the preimpact conditions to produce a disaster’s physical impacts. The physical impacts, in turn, combine with improvised disaster recovery to produce the disaster’s social impacts. Communities can engage in three types of emergency management interventions to ameliorate disaster impacts. Physical impacts can be reduced by hazard mitigation practices and emergency preparedness practices, whereas social impacts can be reduced by recovery preparedness practices.

The following sections describe the components of the model in greater detail. Specifically, the next section will describe the three preimpact conditions—hazard exposure, physical vulnerability, and social vulnerability. This section will be followed by sections discussing hazard event characteristics and improvised disaster responses. The fourth section will discuss disasters’ physical impacts, social impacts, and improvised disaster recovery. The last section will discuss three types of strategic interventions, hazard mitigation practices, emergency preparedness practices, and recovery preparedness practices.

Preimpact Conditions

Hazard Exposure

Hazard exposure arises from people’s occupancy of geographical areas where they could be affected by specific types of events that threaten their lives or property. For natural hazards, this exposure is caused by living in geographical areas as specific as floodplains that sometimes extend only a few feet beyond the floodway or as broad as the Great Plains of the Midwest where tornadoes can strike anywhere over an area of hundreds of thousands of square miles. For technological hazards, exposure can arise if people move into areas where they could be exposed to explosions or hazardous materials releases. In principle, hazard exposure can be measured by the probability of occurrence of a given event magnitude, but these exceedance probabilities can be difficult to obtain for hazards about which the historical data are insufficient to reliably estimate the probability of very unusual events. For example, many areas of the US have meteorological and hydrological data that are limited to the past 100 years, so the estimation of extreme floods requires extrapolation from a limited data series. Moreover, urbanization of the watersheds causes the boundaries of the 100-year floodplains to change in ways that may be difficult for local emergency managers to anticipate. Even more difficult to estimate are the probabilities of events, such as chemical and nuclear reactor accidents, for which data are limited because each facility is essentially unique. In such cases, techniques of probabilistic safety analysis are used to model these systems, attach probabilities to the failure of system components, and synthesize probabilities of overall system failure by mathematically combining the probabilities of individual component failure.

Figure 6-1. Disaster Impact Model.

Source: Adapted from Lindell and Prater (2003)

The greatest difficulties are encountered in attempting to estimate the probabilities of social hazards such as terrorist attacks because the occurrence of these events is defined by social system dynamics that cannot presently be modeled in the same way as physical systems. That is, the elements of social systems are difficult to define and measure. Moreover, the interactions of the system elements have multiple determinants and involve complex lag and feedback effects that are not well understood, let alone precisely measured. Indeed, there are significant social and political constraints that limit the collection of data on individuals and groups. These constraints further inhibit the ability of scientists to make specific predictions of social system behavior.

Physical Vulnerability

Human vulnerability. Humans are vulnerable to environmental extremes of temperature, pressure, and chemical exposures that can cause death, injury, and illness. For any hazard agent—water, wind, ionizing radiation, toxic chemicals, infectious agents—there often is variability in the physiological response of the affected population. That is, given the same level of exposure, some people will die, others will be severely injured, still others slightly injured, and the rest will survive unscathed. Typically, the most susceptible to any environmental stressor will be the very young, the very old, and those with weakened immune systems.

Agricultural vulnerability. Like humans, agricultural plants and animals are also vulnerable to environmental extremes of temperature, pressure, chemicals, radiation, and infectious agents. Like humans, there are differences among individuals within each plant and animal population. However, agricultural vulnerability is more complex than human vulnerability because there is a greater number of species to be assessed, each of which has its own characteristic response to each environmental stressor.

Structural vulnerability. Structural vulnerability arises when buildings are constructed using designs and materials that are incapable of resisting extreme stresses (e.g., high wind, hydraulic pressures of water, seismic shaking) or that allow hazardous materials to infiltrate into the building. The construction of most buildings is governed by building codes intended to protect the life safety of building occupants from structural collapse—primarily from the dead load of the building material themselves and the live load of the occupants and furnishings— but do not necessarily provide protection from extreme wind, seismic, or hydraulic loads. Nor do they provide an impermeable barrier to the infiltration of toxic air pollutants.

Social Vulnerability

The social vulnerability perspective (e.g., Cannon, Twigg & Rowell, 2003; Cutter, Boruff & Shirley, 2003) represents an important extension of previous theories of hazard vulnerability (Burton, et al., 1978). As a concept, social vulnerability has been defined in terms of people’s “capacity to anticipate, cope with, resist and recover from the impacts of a natural hazard” (Wisner, Blakie, Canon & Davis, 2004, p. 11). Whereas people’s physical vulnerability refers to their susceptibility to biological changes (i.e., impacts on anatomical structures and physiological functioning), their social vulnerability refers to their susceptibility to behavioral changes. As will be discussed in greater detail below, these consist of psychological, demographic, economic, and political impacts.

The central point of the social vulnerability perspective is that, just as people’s occupancy of hazard prone areas and the physical vulnerability of the structures in which they live and work are not randomly distributed, neither is social vulnerability randomly distributed—either geographically or demographically. Thus, just as variations in structural vulnerability can increase or decrease the effect of hazard exposure on physical impacts (property damage and casualties), so too can variations in social vulnerability. Social vulnerability varies across communities and also across households within communities. It is the variability in vulnerability that is likely to be of greatest concern to local emergency managers because it requires that they identify the areas within their communities having population segments with the highest levels of social vulnerability.

Event-Specific Conditions

Hazard Event Characteristics

Hazard impacts often are difficult to characterize because a given hazard agent may initiate a number of different threats. For example, tropical cyclones (also known as hurricanes or typhoons) can cause casualties and damage through wind, rain, storm surge, and inland flooding (Bryant, 1991). Volcanoes can impact human settlements through ash fall, explosive eruptions, lava flows, mudflows and floods, and forest fires (Perry & Lindell, 1990; Saarinen & Sell, 1985; Warrick, et al., 1981). However, once these distinct threats have been distinguished from each other, each can be characterized in terms of six significant characteristics. These are the speed of onset, availability of perceptual cues (such as wind, rain, or ground movement), the intensity, scope, and duration of impact, and the probability of occurrence. The speed of onset and availability of perceptual cues affect the amount of forewarning that affected populations will have to complete emergency response actions (Gruntfest, et al., 1978; Lindell, 1994c). In turn, these attributes determine the extent of casualties among the population and the degree of damage to structures in the affected area.

A hazard’s impact intensity can generally be defined in terms of the physical materials involved and the energy these materials impart. The physical materials involved in disasters differ in terms of their physical state—gas (or vapor), liquid, or solid (or particulate). In most cases, the hazard from a gas arises from its temperature or pressure. Examples include hurricane or tornado wind (recall that the atmosphere is a mixture of gases), which is hazardous because of overpressures that can inflict traumatic injuries directly on people. High wind also is hazardous because it can destroy structures and accelerate debris that can itself cause traumatic injuries. Alternatively, the hazard from a gas might arise from its toxicity, as is the case in some volcanic eruptions. Liquids also can be hazardous because of their toxicity, but the most common liquid hazard is water. It is hazardous to structures because of the pressure it can exert and is hazardous to living things when it fills the lungs and prevents respiration. Lava is solid rock that has been liquefied by extreme heat and therefore is hazardous to people and structures because of its thermal energy. Solids also can be hazardous if they take the form of particulates such as airborne volcanic ash or floodborne mud. These are particularly significant because they can leave deposits that have impacts of long duration.

The scope of impact defines the number of affected social units (e.g., individuals, households, and businesses). The probability of occurrence (per unit of time) is another important characteristic that affects disaster impacts indirectly because more probable hazards are likely to mobilize communities to engage in hazard mitigation and emergency preparedness measures to reduce their vulnerability (Prater & Lindell, 2000).

Improvised Disaster Response

Disaster myths commonly portray disaster victims as dazed, panicked, or disorganized but, as will be discussed at greater length in Chapter 8, people actually respond in a generally adaptive manner when disasters strike. Adaptive response is often delayed because normalcy bias delays people’s realization that an improbable event is, in fact, occurring to them. Further delays occur because people have limited information about the situation and, therefore, seek confirmation of any initial indications of an emergency before initiating protective action. In addition, the vast majority of people respond in terms of their customary social units—especially their households and neighborhoods—which usually consumes time in developing social organizations that can cope with the disaster’s demands. Contrary to stereotypes of individual selfishness, disaster victims often devote considerable effort to protecting others’ persons and property. Accordingly, there is considerable convergence on the disaster impact area, as those in areas nearby move in to offer assistance. When existing organizations seem incapable of meeting the needs of the emergency response, they expand to take on new members, extend to take on new tasks, or new organizations emerge (Dynes, 1970).

Improvised Disaster Recovery

Once the situation has stabilized to the point that the imminent threat to life and property has abated, disaster-stricken communities must begin the long process of disaster recovery. Immediate tasks in this process include damage assessment, debris clearance, reconstruction of infrastructure (electric power, fuel, water, wastewater, telecommunications, and transportation networks), and reconstruction of buildings in the residential, commercial, and industrial sectors. Improvised disaster assistance is derived primarily from resources provided by individuals and organizations within the community. The victims themselves might have financial (e.g., savings and insurance) as well as tangible assets (e.g., property) that are undamaged by hazard impact. As one might expect, low-income victims tend to have lower levels of savings, but they also are more likely to be victims of insurance redlining and, thus, have been forced into contracts with insurance companies that go bankrupt after the disaster. Thus, even those who plan ahead for disaster recovery can find themselves without the financial resources they need (Peacock & Girard, 1997). Alternatively, victims can promote their recovery by bringing in additional funds through overtime employment or by freeing up the needed funds by reducing their consumption below preimpact levels. Friends, relatives, neighbors, and coworkers can assist recovery through financial and in-kind contributions, as can community based organizations (CBOs) and local government. In addition, the latter also can provide assistance by means of tax deductions or deferrals.

Disaster Impacts

As noted earlier, disaster impacts comprise physical and social impact. The physical impacts of disasters include casualties (deaths and injuries) and property damage, and both vary substantially across hazard agents. The physical impacts of a disaster are usually the most obvious, easily measured, and first reported by the news media. Social impacts, which include psychosocial, demographic, economic, and political impacts, can develop over a long period of time and can be difficult to assess when they occur. Despite the difficulty in measuring these social impacts, it is nonetheless important to monitor them, and even to predict them if possible, because they can cause significant problems for the long-term functioning of specific types of households and businesses in an affected community. A better understanding of disasters’ social impacts can provide a basis for preimpact prediction and the development of contingency plans to prevent adverse consequences from occurring.

Physical Impacts

Casualties. According to Noji (1997b), hurricanes produced 16 of the 65 greatest disasters of the 20th Century (in terms of deaths) and the greatest number of deaths from 1947-1980 (499,000). Earthquakes produced 28 of the greatest disasters and 450,000 deaths, whereas floods produced four of the greatest disasters and 194,000 deaths. Other significant natural disasters include volcanic eruptions with nine of the greatest disasters and 9,000 deaths, landslides with four of the greatest disasters and 5,000 deaths, and tsunamis with three of the greatest disasters and 5,000 deaths. There is significant variation by country, with developing countries in Asia, Africa, and South America accounting for the top 20 positions in terms of number of deaths from 1966-1990. Low-income countries suffer approximately 3,000 deaths per disaster, whereas the corresponding figure for high-income countries is approximately 500 deaths per disaster. Moreover, these disparities appear to be increasing because the average annual death toll in developed countries declined by at least 75% between 1960 and 1990, but the same time period saw increases of over 400% in developing countries (Berke, 1995).

There often are difficulties in determining how many of the deaths and injuries are “caused by” a disaster. In some cases it is impossible to determine how many persons are missing and, if so, whether this is due to death or unrecorded relocation. The size of the error in estimates of disaster death tolls can be seen in the fact that for many of the most catastrophic events the number of deaths is rounded to the nearest thousand and some even are rounded to the nearest ten thousand (Noji, 1997b). Estimates of injuries are similarly problematic (see Langness, 1994; Peek-Asa, et al., 1998; Shoaf, et al., 1998, regarding conflicting estimates of deaths and injuries attributable to the Northridge earthquake). Even when bodies can be counted, there are problems because disaster impact may be only a contributing factor to casualties with pre-existing health conditions. Moreover, some casualties are indirect consequences of the hazard agent as, for example, with casualties caused by structural fires following earthquakes (e.g., burns) and destruction of infrastructure (e.g., illnesses from contaminated water supplies).

Damage. Losses of structures, animals, and crops also are important measures of physical impacts, and these are rising exponentially in the United States (Mileti, 1999). However, the rate of increase is even greater in developing countries such as India and Kenya (Berke, 1995). Such losses usually result from physical damage or destruction of property, but they also can be caused by losses of land use to chemical or radiological contamination or loss of the land itself to subsidence or erosion. Damage to the built environment can be classified broadly as affecting residential, commercial, industrial, infrastructure, or community services sectors. Moreover, damage within each of these sectors can be divided into damage to structures and damage to contents. It usually is the case that damage to contents results from collapsing structures (e.g., hurricane winds failing the building envelope and allowing rain to destroy the furniture inside the building). Because collapsing buildings are a major cause of casualties as well, this suggests that strengthening the structure will protect the contents and occupants. However, some hazard agents can damage building contents without affecting the structure itself (e.g., earthquakes striking seismically-resistant buildings whose contents are not securely fastened). Thus, risk area residents may need to adopt additional hazard adjustments to protect contents and occupants even if they already have structural protection.

Perhaps the most significant structural impact of a disaster on a stricken community is the destruction of households’ dwellings. Such an event initiates what can be a very long process of disaster recovery for some population segments. According to Quarantelli (1982a), people typically pass through four stages of housing recovery following a disaster. The first stage is emergency shelter, which consists of unplanned and spontaneously sought locations that are intended only to provide protection from the elements, typically open yards and cars after earthquakes (Bolin & Stanford, 1991, 1998). The next step is temporary shelter, which includes food preparation and sleeping facilities that usually are sought from friends and relatives or are found in commercial lodging, although “mass care” facilities in school gymnasiums or church auditoriums are acceptable as a last resort. The third step is temporary housing, which allows victims to re-establish household routines in nonpreferred locations or structures. The last step is permanent housing, which re-establishes household routines in preferred locations and structures.

Households vary in the progression and duration of each type of housing and the transition from one stage to another can be delayed unpredictably, as when it took nine days for shelter occupancy to peak after the Whittier Narrows earthquake (Bolin, 1993). Particularly significant are the problems faced by lower income households, which tend to be headed disproportionately by females and racial/ethnic minorities. Such households are more likely to experience destruction of their homes because of preimpact locational vulnerability. This is especially true in developing countries such as Guatemala (Peacock, Killian & Bates, 1987), but also has been reported in the US (Peacock & Girard, 1997). The homes of these households also are more likely to be destroyed because the structures were built according to older, less stringent building codes, used lower quality construction materials and methods, and were less well maintained (Bolin & Bolton, 1986). Because lower income households have fewer resources on which to draw for recovery, they also take longer to transition through the stages of housing, sometimes remaining for extended periods of time in severely damaged homes (Girard & Peacock, 1997). In other cases, they are forced to accept as permanent what originally was intended as temporary housing (Peacock, et al., 1987). Consequently, there may still be low-income households in temporary sheltering and temporary housing even after high-income households all have relocated to permanent housing (Berke, et al., 1993; Rubin, Sapperstein & Barbee, 1985).

As is the case with estimates of casualties, estimates of losses to the built environment are prone to error. Damage estimates are most accurate when trained damage assessors enter each building to assess the percent of damage to each of the major structural systems (e.g., roof, walls, floors) and the percentage reduction in market valuation due to the damage. Early approximate estimates are obtained by conducting “windshield surveys” in which trained damage assessors drive through the impact area and estimate the extent of damage that is visible from the street, or by conducting computer analyses using HAZUS (National Institute of Building Sciences, 1998). These early approximate estimates are especially important in major disasters because detailed assessments are not needed in the early stages of disaster recovery and the time required to conduct them on a large number of damaged structures using a limited number of qualified inspectors would unnecessarily delay the community recovery process.

Other important physical impacts include damage or contamination to cropland, rangeland, and woodlands. Such impacts may be well understood for some hazard agents but not others. For example, ashfall from the 1980 Mt. St. Helens eruption was initially expected to devastate crops and livestock in downwind areas, but no significant losses materialized (Warrick, et al., 1981). There also is concern about damage or contamination to the natural environment (wild lands) because these areas serve valuable functions such as damping the extremes of river discharge and providing habitat for wildlife. In part, concern arises from the potential for indirect consequences such as increased runoff and silting of downstream river beds, but many people also are concerned about the natural environment simply because they value it for its own sake.

Social Impacts

For many years, research on the social impacts of disasters consisted of an accumulation of case studies, but two research teams conducted comprehensive statistical analyses of extensive databases to assess the long-term effects of disasters on stricken communities (Friesma, et al., 1979; Wright, et al., 1979). The more comprehensive Wright, et al. (1979) study used census data from the 1960 (preimpact) and 1970 (post-impact) censuses to assess the effects of all recorded disasters in the United States. The authors concurred with earlier findings by Friesma, et al. (1979) in concluding no long-term social impact of disasters could be detected at the community level. In discussing their findings, the authors acknowledged their results were dominated by the types of disasters occurring most frequently in the United States—tornadoes, floods, and hurricanes. Moreover, most of the disasters they studied had a relatively small scope of impact and thus caused only minimal disruption to their communities even in the short term. Finally, they noted their findings did not preclude the possibility of significant long-term impacts upon lower levels such as the neighborhood, business, and household.

Nonetheless, their findings called attention to the importance of the impact ratio—the amount of damage divided by the amount of community resources—in understanding disaster impacts. They hypothesized long-term social impacts tend to be minimal in the US because most hazard agents have a relatively small scope of impact and tend to strike undeveloped areas more frequently than intensely developed areas simply because there are more of the former than the latter. Thus, the numerator of the impact ratio tends to be low and local resources are sufficient to prevent long-term effects from occurring. Even when a disaster has a large scope of impact and strikes a large developed area (causing a large impact ratio in the short term), state and federal agencies and NGOs (e.g., American Red Cross) direct recovery resources to the affected area, thus preventing long-term impacts from occurring. For example, Hurricane Andrew inflicted $26.5 billion in losses to the Miami area, but this was only 0.4% of the US GDP (Charvériat, 2000). Recovery problems described in the studies reported in Peacock, Morrow and Gladwin (1997) were determined more by organizational impediments than by the lack of resources.

Psychosocial impacts. Research reviews conducted over a period of 25 years have concluded that disasters can cause a wide range of negative psychological responses (Bolin 1985; Gerrity & Flynn, 1997; Houts, Cleary & Hu, 1988; Perry & Lindell, 1978). These include psychophysiological effects such as fatigue, gastrointestinal upset, and tics, as well as cognitive signs such as confusion, impaired concentration, and attention deficits. Psychological impacts include emotional signs such as anxiety, depression, and grief. They also include behavioral effects such as sleep and appetite changes, ritualistic behavior, and substance abuse. In most cases, the observed effects are mild and transitory—the result of “normal people, responding normally, to a very abnormal situation” (Gerrity & Flynn 1997, p. 108). Few disaster victims require psychiatric diagnosis and most benefit more from a crisis counseling orientation than from a mental health treatment orientation, especially if their normal social support networks of friends, relatives, neighbors, and coworkers remain largely intact. However, there are population segments requiring special attention and active outreach. These include children, frail elderly, people with pre-existing mental illness, racial and ethnic minorities, and families of those who have died in the disaster. Emergency workers also need attention because they often work long hours without rest, have witnessed horrific sights, and are members of organizations in which discussion of emotional issues may be regarded as a sign of weakness (Rubin, 1991). However, as Chapter 11 will indicate, there is little evidence of emergency workers needing directive therapies either.

The negative psychological impacts described above, which Lazarus and Folkman (1984) call emotion focused coping, generally disrupt the social functioning of only a very small portion of the victim population. Instead, the majority of disaster victims engage in adaptive problem focused coping activities to save their own lives and those of their closest associates. Further, there is an increased incidence in prosocial behaviors such as donating material aid and a decreased incidence of antisocial behaviors such as crime (Drabek, 1986; Mileti, et al., 1975; Siegel, et al., 1999). In some cases, people even engage in altruistic behaviors that risk their own lives to save the lives of others (Tierney, et al., 2001).

There also are psychological impacts with long-term adaptive consequences, such as changes in risk perception (beliefs in the likelihood of the occurrence a disaster and its personal consequences for the individual) and increased hazard intrusiveness (frequency of thought and discussion about a hazard). In turn, these beliefs can affect risk area residents’ adoption of household hazard adjustments that reduce their vulnerability to future disasters. However, these cognitive impacts of disaster experience do not appear to be large in aggregate, resulting in modest effects on household hazard adjustment (see Lindell & Perry, 2000 for a review of the literature on seismic hazard adjustment, and Lindell & Prater 2000; Lindell & Whitney, 2000; and Whitney, Lindell & Nguyen, 2004 for more recent empirical research).

Demographic impacts. The demographic impact of a disaster can be assessed by adapting the demographic balancing equation, Pa Pb = BD + IMOM, where Pa is the population size after the disaster, Pb is the population size before the disaster, B is the number of births, D is the number of deaths, IM is the number of immigrants, and OM is the number of emigrants (Smith, Tayman & Swanson, 2001). The magnitude of the disaster impact, Pa Pb, is computed for the population of a specific geographical area and two specific points in time. Ideally, the geographical area would correspond to the disaster impact area, Pb would be immediately before disaster impact, and Pa would be immediately after disaster impact. In practice, population data are available for census divisions (census block, block group, tract, or larger area), so a Geographical Information System (GIS) must be used to estimate the impact on the impact area. Moreover, population data are likely to be most readily available from the decennial censuses, so the overall population change and its individual demographic components—births, deaths, immigration, and emigration—are likely to be estimated from that source (e.g., Wright, et al., 1979). On rare occasions, special surveys have been conducted in the aftermath of disaster (e.g., Peacock, Morrow & Gladwin, 1997). The limited research available on demographic impacts (Friesma, et al., 1979; Wright, et al., 1979) suggests disasters have negligible demographic impacts on American communities, but the highly aggregated level of analysis in these studies does not preclude the possibility of significant impacts at lower levels of aggregation (census tracts, block groups, or blocks). Although it is logically possible that disasters could affect the number of births, it does not seem likely that the effect would be large. Moreover, as noted in the previous section on physical impacts, the number of deaths from disasters in the United States has been small relative to historical levels (e.g., the 6000 deaths in the 1900 Galveston hurricane were approximately 17% of the city’s population) or to the levels reported in developing countries. The major demographic impacts of disasters are likely to be the (temporary) immigration of construction workers after major disasters and the emigration of population segments that have lost housing. In many cases, the housing-related emigration is also temporary, but there are documented cases in which housing reconstruction has been delayed indefinitely—leading to “ghost towns” (Comerio, 1998). Other potential causes of emigration are psychological impacts (belief that the likelihood of disaster recurrence is unacceptably high), economic impacts (loss of jobs or community services), or political impacts (increased neighborhood or community conflict).

Economic impacts. The property damage caused by disaster impact creates losses in asset values that can be measured by the cost of repair or replacement (Committee on Assessing the Costs of Natural Disasters, 1999). Disaster losses in United States are initially borne by the affected households, businesses, and local government agencies whose property is damaged or destroyed. However, some of these losses are redistributed during the disaster recovery process. There have been many attempts to estimate the magnitude of direct losses from individual disasters and the annual average losses from particular types of hazards (e.g., Mileti, 1999). Unfortunately, these losses are difficult to determine precisely because there is no organization that tracks all of the relevant data and some data are not recorded at all (Charvériat, 2000; Committee on Assessing the Costs of Natural Disasters, 1999). For insured property, the insurers record the amount of the deductible and the reimbursed loss, but uninsured losses are not recorded so they must be estimated—often with questionable accuracy.

The ultimate economic impact of a disaster depends upon the disposition of the damaged assets. Some of these assets are not replaced, so their loss causes a reduction in consumption (and, thus, a decrease in the quality of life) or a reduction in investment (and, thus, a decrease in economic productivity). Other assets are replaced—either through in-kind donations (e.g., food and clothing) or commercial purchases. In the latter case, the cost of replacement must come from some source of recovery funding, which generally can be characterized as either intertemporal transfers (to the present time from past savings or future loan payments) or interpersonal transfers (from one group to another at a given time). Some of the specific mechanisms for financing recovery include obtaining tax deductions or deferrals, unemployment benefits, loans (paying back the principal at low- or no-interest), grants (requiring no return of principal), insurance payoffs, or additional employment. Other sources include depleting cash financial assets (e.g., savings accounts), selling tangible assets, or migrating to an area with available housing, employment, or less risk (in some cases this is done by the principal wage earner only).

In addition to direct economic losses, there are indirect losses that arise from the interdependence of community subunits. Research on the economic impacts of disasters (Alesch, et al., 1993; Dacy & Kunreuther, 1969; Dalhamer & D’Sousa, 1997; Durkin, 1984; Gordon, et al., 1995; Kroll, et al., 1991; Lindell & Perry, 1998; Nigg, 1995; Tierney, 1997a) suggests the relationships among the social units within a community can be described as a state of dynamic equilibrium involving a steady flow of resources, especially money. Specifically, a household’s linkages with the community are defined by the money it must pay for products, services, and infrastructure support. This money is obtained from the wages that employers pay for the household’s labor. Similarly, the linkages that a business has with the community are defined by the money it provides to its employees, suppliers, and infrastructure in exchange for inputs such as labor, materials and services, and electric power, fuel, water/wastewater, telecommunications, and transportation. Conversely, it provides products or services to customers in exchange for the money it uses to pay for its inputs.

It also is important to recognize the financial impacts of recovery (in addition to the financial impacts of emergency response) on local government. Costs must be incurred for tasks such as damage assessment, emergency demolition, debris removal, infrastructure restoration, and re-planning stricken areas. In addition to these costs, there are decreased revenues due to loss or deferral of sales taxes, business taxes, property taxes, personal income taxes, and user fees.

Political impacts. There is substantial evidence that disaster impacts can cause social activism resulting in political disruption, especially during the seemingly interminable period of disaster recovery. The disaster recovery period is a source of many victim grievances and this creates many opportunities for community conflict, both in the US (Bolin 1982, 1993) and abroad (Bates & Peacock 1988). Victims usually attempt to recreate preimpact housing patterns, but it can be problematic for their neighbors if victims attempt to site mobile homes on their own lots while awaiting the reconstruction of permanent housing. Conflicts arise because such housing usually is considered to be a blight on the neighborhood and neighbors are afraid the “temporary” housing will become permanent. Neighbors also are pitted against each other when developers attempt to buy up damaged or destroyed properties and build multifamily units on lots previously zoned for single family dwellings. Such rezoning attempts are a major threat to the market value of owner-occupied homes but tend to have less impact on renters because they have less incentive to remain in the neighborhood. There are exceptions to this generalization because some ethnic groups have very close ties to their neighborhoods, even if they rent rather than own.

Attempts to change prevailing patterns of civil governance can arise when individuals sharing a grievance about the handling of the recovery process seek to redress that grievance through collective action. Consistent with Dynes’s (1970) typology of organizations, existing community groups with an explicit political agenda can expand their membership to increase their strength, whereas community groups without an explicit political agenda can extend their domains to include disaster-related grievances. Alternatively, new groups can emerge to influence local, state, or federal government agencies and legislators to take actions that they support and to terminate actions that they disapprove. Indeed, such was the case for Latinos in Watsonville, California following the Loma Prieta earthquake (Tierney, et al., 2001). Usually, community action groups pressure government to provide additional resources for recovering from disaster impact, but may oppose candidates’ re-elections or even seek to recall some politicians from office (Olson & Drury, 1997; Prater & Lindell, 2000; Shefner, 1999). The point here is not that disasters produce political behavior that is different from that encountered in normal life. Rather, disaster impacts might only produce a different set of victims and grievances and, therefore, a minor variation on the prevailing political agenda (Morrow & Peacock, 1997).

Emergency Management Interventions

As Figure 6-1 indicates, there are three types of preimpact interventions that can effect reductions in disaster impacts. Hazard mitigation and emergency preparedness practices directly reduce a disaster’s physical impacts (casualties and damage) and indirectly reduce its social impacts, whereas recovery preparedness practices directly reduce a disaster’s social impacts. Improvised disaster response actions also directly affect disasters’ physical impacts but, by their very nature, are likely to be much less effective than planned interventions. Similarly, improvised recovery assistance directly affects disasters’ social impacts but is likely to be less effective than systematic recovery preparedness practices.

Figure 6-1 includes the four “phases” of emergency management—mitigation, preparedness, response, and recovery—but makes it clear there is a complex relationship between them. In reality, these “phases” might better be called functions, since they are neither discrete nor temporally sequential. Later chapters will address hazard mitigation (Chapter 7), emergency preparedness (Chapter 9), emergency response (Chapter 10), and disaster recovery (Chapter 11) in greater detail. However, this section will provide a brief description of each of these functions and their interrelationships.

Hazard Mitigation Practices

One way to reduce the physical impacts of disasters is to adopt hazard mitigation practices. These can be defined as preimpact actions that protect passively against casualties and damage at the time of hazard impact (as opposed to an active emergency response). Hazard mitigation includes hazard source control, community protection works, land use practices, building construction practices, and building contents protection. Hazard source control acts directly on the hazard agent to reduce its magnitude or duration. For example, patching a hole in a leaking tank truck prevents a gas from being released. Community protection works, which limit the impact of a hazard agent on an entire community, include dams and levees that protect against floodwater and sea walls that protect against storm surge. Land use practices reduce hazard vulnerability by avoiding construction in areas that are susceptible to hazard impact. The use of the term land use practices instead of land use regulations is deliberate. Landowners can adopt sustainable practices whether or not they are required to do so. Thus, government agencies can encourage the adoption of appropriate land use practices by providing incentives to encourage development in safe locations, establishing sanctions to prevent development in hazardous locations, or engaging in risk communication to inform landowners about the risks and benefits of development in locations throughout the community.

Hazard mitigation can also be achieved through building construction practices that make individual structures less vulnerable to natural hazards. Here too, the use of the term building construction practices rather than building codes is deliberate because building owners can adopt hazard resistant designs and construction materials in the absence of government intervention. Disaster resistant construction practices include elevating structures out of flood plains, designing structures to respond more effectively to lateral stresses, and providing window shutters to protect against wind pressure and debris impacts. Government agencies can encourage the adoption of appropriate building construction practices by providing incentives to encourage appropriate designs and materials, establishing code requirements for hazard resistant building designs and materials, or informing building owners about the risks and benefits of different building designs and materials. Finally, hazard mitigation can be achieved by contents protection strategies such as elevating appliances above the base flood elevation or bolting them to walls to resist seismic forces.
Emergency Preparedness Practices

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