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Natural Disasters

Natural Disasters


A natural hazard is an extreme natural phenomenon that threatens human lives, activities or property, or the environment of life. Natural disasters are the destructive consequence of extreme natural hazards, and globally there are more than 700 of them each year. Floods are the most common natural disaster. Together with earthquakes and cyclonic storms they are the most destructive of such manifestations.

Natural phenomena may be transformed into hazards either by excess or by dearth. For example, too great a discharge of water may give rise to flooding, whereas too little may cause a drought. A situation becomes hazardous when the physical forces or environmental stresses at work exceed the ability of human social, economic, cultural, or health systems to absorb, resist, or avoid the resulting negative impact. In this respect, natural hazards are defined not only by the natural forces that induce them, but also by the vulnerability of human systems. Vulnerability is defined here as the susceptibility of people or things to harm.

The threat of a natural hazard is either constantly present or is subject to fluctuations. Many hazards are cyclical; for example, earthquakes of a certain size will occur on a given fault when enough tectonic stress has been accumulated to overcome the frictional resistance of the rock mass to slipping, a process which will probably occur with a definable time interval because of the gradual build-up of strain on the fault. Other hazards, especially meteorological ones, may be seasonal.

Generally, the vast majority of hazards are subject to a rule of magnitude and frequency in which the higher the magnitude, the lower the frequency of occurrence. Some hazards, such as volcanic eruptions, may operate on a geological timescale that is much longer than the scale of human lives. In such cases it can be very difficult to justify the allocation of resources to prepare effectively for events that have a low probability of occurrence during a single human lifetime.

In other cases, the repetitiveness of a hazard may be a problem. For instance, the solvency of the U.S. National Flood Insurance Program (NFIP) depends as much on reducing the instance of repeated claims as it does on anticipating and reducing the impact of large, infrequent events. In a small number of cases, claims have been made for reimbursing damage to a single property up to five times in a decade. Such problems must be abated by reducing either the hazard or the vulnerability to it.

In everyday situations the product of hazard and vulnerability is risk, which can be defined as the probability or likelihood that an event of a given kind and size will occur in a given interval of time and with an anticipated set of negative consequences. Engineers tend to define risk by calculating numerical values of the probability, while social scientists may be more interested in how risk is perceived and how some of the intangible features of human behavior affect it. In any event, paradoxically, risk is a hypothetical quantity (though no less important for that). It materializes as impact, which should lead to an emergency response that reduces the harm done as much as possible. Hence:

Hazard × Vulnerability [× Exposure] = Risk Impact Emergency Response

Exposure to natural hazards becomes an issue when an item (such as a person, a community, a building, or an economic activity) is not constantly at risk. Despite temporal variations in strain upon Earths crust, to all intents and purposes we may consider earthquake risk to be fairly constant, especially as it cannot accurately be predicted in the short term. However, predictable hazards such as hurricanes, which can be monitored and tracked before they make landfall (i.e., arrive at a coast), may allow a forecast to be turned into a warning that stimulates an organized response on the part of the threatened community. Generally, where it is feasible, evacuation is the most effective means of reducing the exposure of people to death or injury in high magnitude events.

The question of exactly what phenomena should be classified as natural hazards has long been debated by students of the field. The core phenomena consist of geophysical events from the atmosphere, hydrosphere, and geosphere (the lithosphere), and to a lesser extent from the biosphere. Earthquakes, landslides, and subsidence of the ground are geospheric hazards of the first order; tropical cyclones (also known as hurricanes and typhoons), tornadoes, and windstorms are the leading examples of meteorological hazards; and drought and floods are the principal threats from the hydrosphere, with subdivision of the latter into riverine, rain-fed, coastal, and glacial outburst forms.

By convention, though not necessarily on the basis of any very robust theoretical reasoning, disease outbreaks in humans, animals, and plants (i.e., epidemics, epizootics, and epiphytotics) are not usually classified as natural hazards. However, locust infestations are often included.

A further definitional problem occurs when disasters have mixed natural and human-induced (anthropogenic) causes. For example, destructive floods can result from dam bursts, which can in turn result from excessive river flows, earthquakes, or rapid landslides or snow avalanches that cause water waves in the reservoir, if not from failure of the materials or design of the dam itself. In point of fact, natural hazard and natural disaster are convenience terms. Whatever ones religious convictions, responsibility for damage and destruction cannot be shrugged off by referring to unpredictable acts of God, as they stem from failure to mitigate forms of human and environmental vulnerability that are well known and understood.

In conceptual terms, serious study of natural hazards began in the 1920s with the development of the human ecology field. From 1945 onward the Chicago school founded by Harlan Barrows (18771960) and taken forward by Gilbert Fowler White (19112006) gradually revealed the human perceptual and social processes of adjusting to hazards. White and his students found a rich source of study in the struggles of U.S. Great Plains farmers to adapt to varying patterns of drought and flood. By and large, research in many other parts of the world has confirmed the findings of the U.S. human ecologists and geographers, despite some variations due to cultural differences. Thus, the hazardousness of place is tempered by the choice of adjustments that people who inhabit zones of hazard are able to employ.

The Chicago school was motivated to explain why structural responses had not solved the problem of natural hazards. For example, a century of canalization and levee building by the U.S. Army Corps of Engineers on the Mississippi River ended in 1993 with the worst and most prolonged flood on record. Clearly residents, developers, and planners on the floodplain had made some false assumptions about the infallibility of structural flood defenses.

With some success White and his colleagues advocated an approach based on a mixture of structural and nonstructural protection. It may still be necessary to build barriers to stop flooding, or to strengthen buildings so that they resist earthquakes, but it is equally necessary to tackle such hazards with organizational methods. Hence the nonstructural solutions include evacuation (where feasible), emergency planning, land-use control, and public awareness campaigns.

Unfortunately, despite the best efforts of mitigation specialists, the world has not become less susceptible to hazards over the last half-century. For example, Hurricane Katrina, which made landfall in Louisiana and Mississippi on August 29, 2005, killed 1,848 people, seriously damaged or destroyed 78,000 homes, and left more than half of the population of New Orleans without shelter. As Hurricane Ivan had narrowly missed crossing the city a year previously, the scenario for a major storm impact was well known. Despite this, the heights and state of maintenance of levees were insufficient, as were evacuation and recovery plans. Failures of coordination between local, state, and federal levels of government led to a relief debacle. Rebuilding will probably take eight to eleven years and, due to the phenomenon of geographical inertia (the reluctance of long-term residents to relocate their homes and businesses), will necessarily require considerable investment in major yet fallible structural defenses.

The relentless rise in global population, polarization of wealth between rich and poor, marginalization of vulnerable communities, and the prevalence of about twenty-five complex humanitarian emergencies have all contributed to the increasing toll of natural disasters. So has the increasing complexity and interdependence of modern society, and so, no doubt, will global warming and climate change, as more extreme, if not more frequent, meteorological phenomena are likely to occur.

The average annual death toll in natural disasters is about 140,000, but there is very considerable variation from one year to another. In fact, after five years in which the death toll averaged about 58,000, the Asian tsunami of December 26, 2004, took at least 230,000 lives. Despite the irregularities, there are discernible upward trends in the number of people directly affected by natural disasters (at least 250 million a year) and the cost of disasters (well in excess of US$100 billion a year), although improved protection has had some effect in stemming the rise in mortality.

Despite much debate and many good intentions, global vulnerability to natural hazards remains unacceptably high. Critical facilitiesschools, hospitals, essential lifelinesremain heavily at risk in many countries (for example, in the Kashmir earthquake of October 5, 2005, schools frequented by 48,000 children collapsed). More money continues to be spent on responding to disasters than on reducing the risks of future ones. Although vulnerability and poverty are not precisely synonymous, in both rich and poor countries they are very closely linked. Hence natural disaster impacts involve serious questions of equity. Natural hazard impacts need to be mitigated by a mixture of prevention, avoidance, and sustainable development: In short, sustainable disaster reduction is required.

SEE ALSO Disaster Management; Shocks


Abbott, Patrick L. 2004 Natural Disasters. 4th ed. New York: McGraw-Hill.

Alexander, David E. 1993. Natural Disasters. London and New York: Routledge.

Burton, Ian, Robert W. Kates, and Gilbert F. White. 1993. The Environment as Hazard. 2nd ed. New York: Guilford.

Perry, Ronald W., and Enrico L. Quarantelli, eds. 2005. What Is a Disaster? New Answers to Old Questions. Philadelphia: Xlibris.

David Alexander

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Natural Disasters


Natural disasters occur when forces of nature damage the environment and manmade structures. If people live in the area, natural disasters can cause a great deal of human suffering. As a result of disasters, people may be injured or killed, or may lose their homes and possessions. The impact is so great that the affected community often must depend on outside help in order to cope with the results (Noji, Gunn and William). Examples of natural forces that can cause widespread human suffering include earthquakes, tornadoes, hurricanes, floods, volcanic eruptions, wilderness fires, and extreme hot or cold temperatures. Between 1975 and 1996, natural disasters worldwide cost 3 million lives and affected at least 800 million others (Noji). In the United States, damage caused by natural hazards costs close to one billion dollars per week.


The physical force of a disaster can directly cause injury and death to the population, and each type of disaster can result in its own combination of physical injuries. In earthquakes, buildings and the objects inside them can fall, injuring those who live or work there. Floods can result in drowning, and wildfires can cause burns and illness from smoke inhalation. In addition to the direct injury and death caused by the disaster's force, there can be other serious adverse effects on the well being of those living in the area.

The large numbers of people who are suddenly ill or injured can exceed the capacity of the local health care system to care for them. In addition to the burden of increased numbers of patients, the system itself can become a victim of the disaster. Hospitals may be damaged, roads blocked, and personnel may be unable to perform their duties. The loss of these resources occurs at a time when they are most critically needed.

The disaster also can hamper the ability to provide routine, non-emergency health services. Many people may be unable to obtain care and medications for their ongoing health problems. The disruption of these routine services can result in an increase in illness and death in segments of the population that might not have been directly affected by the disaster.

Much has been written about the mental health aspects of natural disasters. The popular images of a community paralyzed by the shock of the disaster, panicking or looting, are unfounded. Actually, people tend to come together following a natural disaster. Survivors offer immediate assistance to those who are injured or trapped in earthquake damaged buildings, help with sandbagging efforts in floods, offer shelter and assistance to those made homeless, and volunteer goods or money to those in need. However, living in a disaster area can be highly stressful. Staying in damaged buildings, relocating to shelters, dealing with the death or injuries of loved ones, as well as the prolonged time and energy involved in recovering from the affects of the disaster can result in feelings of anxiety and depression. While these might be normal responses to stress and unpleasant events, the degree to which a disaster can disrupt daily living may contribute to an increase in these feelings.


Certain disasters can interfere with the functioning of water and sewage systems as well as the provision of gas and electricity. The loss of these everyday services can increase the risk for sickness even in uninjured people. For example, drinking unclean water or eating inadequately stored or prepared food can cause serious intestinal illness.

The most serious consequences of natural disasters are related to mass population displacements. Many people cannot stay in their homes because the buildings are so badly damaged that they are structurally unsafe. Others refuse to stay in otherwise stable buildings because they fear that they might collapse. While this often occurs following violent storms, it is particularly the case after earthquakes, when potentially damaging aftershocks commonly occur. In many cases, those displaced by disasters find shelter in the homes of people they know, while others must go to shelters staffed by disaster relief authorities such as Red Cross/Red Crescent Societies and government agencies.

Placing large numbers of people in crowded shelters poses a risk for additional health problems. It can be difficult to provide so many people with clean drinking water, sufficient waste disposal, and safe, nutritious food. This temporary living situation can also increase the chances for outbreaks of certain diseases. It is important to remember that only those diseases that are found in the affected community during predisaster times pose a danger to displaced populations after a disaster occurs. For example, it would be unlikely for those living in a shelter following a flood in the upper Midwest portion of the United States to experience an outbreak of malaria (as malaria does not exist in that part of the world), but poor sanitary services could contribute to an outbreak of conditions such as infectious diarrhea or some forms of respiratory illness. In addition, an occasional outbreak of more serious illnesses that might occasionally appear in the community during nondisaster times, such as meningitis or measles, would be a more significant health risk in shelters.

When large numbers of people gather in unsheltered settings, such as parks or open fields, there is an even greater risk of illness. This is because these areas often do not have enough sanitary services. Clean drinking water may have to be trucked into the area, and prompt attention must be directed to providing facilities to handle human waste. The ability to receive, safely store, and prepare food is also a concern for the health of the displaced population. Flies, mosquitoes, and rodents that might be carrying diseases that can cause illness in humans add to the risk of living in an unsheltered setting.


The impact of a disaster on the public's health poses special problems for public health professionals. They must monitor the health needs of the disaster-affected population and work to ensure that emergency managers take actions to meet those needs. They also need to maintain the everyday public health programs that were in place before the disaster occurred. These challenges can be addressed in several ways.

Rapid assessment surveys can be conducted of those living in areas most impacted by the disaster. Often, aerial views of the disaster area can indicate damage to key facilities (hospitals, utility stations, major roads), residential structures, and the assembly of large numbers of people in unsheltered settings. Teams of public health, engineering, social service, and medical personnel can then go to those areas that appear most damaged and begin a survey of the people living there. The affected area is divided into smaller areas, called clusters. The teams interview a representative sample of seven people from each of thirty different clusters in the high-impact disaster area. Using a standard set of questions, they gather information about the number of injuries, deaths, houses without running water, functioning toilets, electricity, heat, and those with ongoing medical conditions (Malilay). With the information gathered from the assessment surveys, disaster health managers can draw conclusions about which segments of the affected community are at greatest need for emergency efforts. Once the decision is made to direct resources to the most seriously affected areas, another rapid assessment may be performed to determine the effectiveness of those efforts.

Other information about the number and types of injured may be obtained from medical facilities. It is important to distinguish between patients who were injured or made ill as a result of the disaster from those who happened to seek medical attention for conditions not related to the disaster. This requires a working knowledge of the injury and illness patterns that are associated with different natural disasters. Definitions of which types of conditions will be attributed directly to the disaster or its consequences also are needed.

Computer models are being developed that can combine views of buildings, transportation ways (highways, railroads, airports, and harbors), utilities, and medical facilities with local hazards of varying severity. These models, currently being tested for earthquakes, allow emergency managers and health planners to predict the extent of damage and injuries if a hazard occurs in their community. Once these models are refined and validated, they may prove valuable to emergency response and public health planners.

As the global population continues to grow and more people live in hazard-prone areas, there will be an increase in the number and severity of mass population emergencies. Public health personnel have a key role in natural disaster preparation and response. Before a disaster occurs, they need to have systems in place to identify and track diseases. They must also understand the basic health issues of water and food safety, sanitation, and environmental hazards.

Public health practitioners routinely provide comprehensive programs of health education and preventive care that put them in close contact with those living in the community. They can use their professional skills to develop and evaluate programs for community disaster preparedness before a disaster strikes. After the disaster, they have the ability to help assess its affects on the local population. By adapting their knowledge and skills to these large-scale emergencies, public health professionals can have a significant impact on reducing the negative health affects of disasters.

Steven J. Rottman

Kimberley Shoaf

(see also: Famine; Refugee Communities; War )


Gunn, S., and William, A. (1990). Multilingual Dictionary of Disaster Medicine and International Relief. London: Kluwer Academic.

Malilay, J.; Flanders, W. D.; and Brogan, D. (1996). "A Modified Cluster-Sampling Method for Post-Disaster Rapid Assessment of Needs." Bulletin of the World Health Organization 74(4):399405.

Noji, Eric K. (1997). The Public Health Consequences of Disasters. New York: Oxford University Press.

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