In this chapter - Type and magnitude of event | Types of response | Timescale of response | Natural hazard life-cycle | Relief, rehabilitation and reconstruction | Contingency planning | Contrasting hazard experiences - the case of drought | Single and multiple hazards | Hazard ecology

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Our experience of natural hazards varies from one type of hazard to another. The nature of the hazard event and the environmental processes giving rise to it strongly influence how (and how long) we are affected, what the main sources of danger are, and how we can protect ourselves and our property.

Type and magnitude of event

One key factor is the suddenness of the event. Slow events can be coped with much easier; warnings can be issued, people evacuated if necessary, contingency plans drawn up. The sudden and unexpected event is much more likely to bring devastating loss of life, injury and property damage.

An interesting example of the slow and cumulative build-up of a hazard event over a long period is the Leaning Tower of Pisa, in Italy. The tower is built on a deep layer of clay, and soon after building work began in 1173 the structure was found to lean because of compression of the underlying material. Work stopped just above the third level in 1185, and it began again in 1274. Seven levels had been completed when work stopped in 1284 because tilting was accelerating. Work on the bell tower started in 1350, and it was completed in 1355. The 59 m high tower tilts at 5 degrees from the vertical, and it is tilting further at a rate of 0.02 m per year. The subsidence promoted the tower's famous lean, but it also led to an overall sinking of 2 m so that the tower is now entered below present-day ground level. Because the hazard event was slow and cumulative, adjustments could be made during the course of construction of one of the world's most famous hazard products, and one of its unchallenged wonders. Ironically it proved necessary in 1989 to close the tower temporarily, to allow additional remedial work (to improve safety and sbaility of the structure) to be carried out.

Contemporary examples of the slow build-up of problems include the drought in north Africa during most of the 1980s, and the threat of world-wide sea level rise caused by atmospheric warming stemming from air pollution. Projected sea level rise threatens the coastline of Britain in many different ways.

The sudden event, unheralded and entirely unexpected, is a very different experience. The most catastrophic seismic disaster yet experienced in the western hemisphere occurred in Peru on 31st May 1970. The earthquake - sometimes referred to as "The Great Peruvian Earthquake" - was caused by a fault rupture some 50 km deep in an offshore trench, and its impact was felt over an area of about 75,000 km2 in west and central Peru. The human toll was high - over 50,000 dead, a similar number injured and an estimated 800,000 temporarily homeless. Over 200,000 homes and buildings were destroyed. The earthquake triggered off a massive debris avalanche from Huascaran Mountain, which sent a mass of about 50 million m3 of rock, snow, ice and soil moving down-valley at over 300 km h-1. Over 18,000 people living in the towns of Yungay and Ranrahirca were buried almost instantaneously by up to 3 m of fluid debris.

The 1986 Chernobyl nuclear power plant explosion (Figure 2) was also a sudden event, with no prior warning.

Experiences also reflect the severity of the hazard involved. Relatively small scale events tend to produce less dramatic experiences than larger but less frequent occurrences of the same hazard. For example, winter blizzards and snow storms occur fairly regularly in Scotland, which normally copes well. But extreme conditions demand special attention. The very severe blizzards and snow storms of the 30th January 1978 in north-east Scotland created much greater stress than normal and seventeen helicopter rescue teams from the RAF, Navy and Army were needed to rescue sick people, check isolated farmsteads and deliver food and fodder to remote areas. Blizzard conditions also created problems in New England, USA, early in 1978.

Types of response

Human response during and after hazards fall into two categories - biomedical and psychosocial. The former includes immediate impacts like death and direct and indirect forms of injury; but it also includes longer-term impacts such as the need for shelter and food and the provision of basic amenities of hygiene and medical care and attention. The psychosocial response describes the way in which we react to a hazard event through patterns of behaviour and perception both during and after the event. Increased personal anxiety and worry, loss of community cohesion and attribution of blame to others are common responses in hazard situations.

The biomedical and psychosocial responses to any given hazard event differ in character, magnitude and significance. The latter, for example, affect more people (directly and indirectly), and have an impact over a wider area than that directly affected by the event, where most of the biomedical impacts are usually concentrated.

Timescale of response

Experience of a hazard event is not confined to the event itself; almost without exception there are longer-term impacts and consequences. The recovery time in the wake of a hazard event can be very prolonged and significant. For example, salt water flooded arable fields along the North Sea coast of England and the Netherlands in 1953, and it was several years before they were leached enough to grow crops again.

Delayed impacts also include loss of life. An estimated 830,000 people died as a result of the Shensi earthquake of 23rd January 1556 which devastated the Chinese city of Hsian. Many were killed in the sudden collapse of the loess caves where most families were sleeping when the earthquake struck without warning at 5 am., but many others died after the event as a result of long-term demoralisation, famine and disease.

Natural hazard life-cycle

The different experiences and activities during and after a hazard event can be visualised in terms of a life-cycle. For any natural hazard, the life-cycle has three main phases of reaction - during the event; immediately following the event; and between successive events.

Reactions during events are important because they determine the scale and diversity of death and injury to humans and damage to property. Such reactions often involve emergency actions to evacuate, rescue and bring relief to the people involved. Reactions immediately following the event and within the following days and weeks are also critical because they determine how fast and how effectively life can be returned to normal. Longer-term reactions include the provision of control works, land-use zoning and hazard insurance schemes.

Relief, rehabilitation and reconstruction

Experience of natural hazards generally involves a series of activities which are inter-related, may overlap in time and may exist for different periods of time in different hazard settings (Figure 8). Whilst precise details of what happens when will depend on the type, magnitude, location and timing of the hazard event, a common pattern can be detected.

Figure 8. Response to hazard events. The figure shows the pattern of changes in various indicators of disruption at different phases of the hazard event, with the overall trend of recovery towards normality.

Before a hazard event normality prevails, with quality of life for locals, level of economic activity and social cohesion and stability having built up naturally over a period of stability. When the hazard strikes normality is disrupted, often immediately and totally.

The relief or emergency period (phase one of the life-cycle) starts straight away. During the first few hours and days efforts are made to provide food, water, clothing, shelter and medical care to all inhabitants of the affected area, and to stop continued loss and disruption directly related to the event (such as the collapse of damaged buildings, or the spread of fire or infectious disease). The emphasis during the disaster relief phase is on speed and efficiency, and mistakes can be made despite efforts to make rational decisions in the face of panic reactions and lack of time, resources and full information and understanding.

Relief teams from outside the immediate area may arrive to help or organize search, rescue and care operations. Urgent supplies of medical drugs and equipment, rescue equipment, clothing and food may be flown in; for example an estimated $10,750,000 in international aid was poured into Mexico to cope with relief operation after the 1985 earthquake (Table 5). International relief agencies such as the Red Cross provide vital logistical, medical and humanitarian support during this critical initial phase of disaster response.

Table 5 International aid received during the Mexico City earthquake, 20-30 September 1985

type of aid






clothing and blankets






rescue equipment






machinery and vehicles



medical instruments






SOURCE: Zeballos (1986)

 After relief comes the rehabilitation period (phase two), which might last for several weeks or months. Actions are designed to restore physical and community structures to at least a temporary return to normality (Figure 8). Mass shelter is replaced by temporary housing, the injured are transferred from field hospitals to regular hospitals, money and resources are made available to the unemployed and dispossessed. More complex than the relief, rehabilitation requires accurate assessment of needs and carefully co-ordinated planning of responses. The risk of recurrent disasters commonly remains during this phase - if the hazard strikes again, or wider (and less obvious) impacts of the event were not identified and at least partially catered for (such as the spread of infectious disease because of inadequate sanitary provision).

Rehabilitation efforts are normally planned and executed locally. Only in exceptional circumstances are international initiatives involved, like the world-wide Band Aid events to fund rehabilitation during and after the mid-1980s Ethiopian drought. More recently initiatives such as Comic Relief have contributed much needed resources in many disaster-damaged areas.

Through time rehabilitation gives way to reconstruction (phase three), when permanent changes are introduced to restore the quality of life and economic stability to at least its original level, if not to improve on the past by creating better economic opportunities and a higher quality of life. Three criteria dictate the nature of these activities and the speed at which they are carried out:

The speed and efficiency of recovery after disaster varies according to type and magnitude of the hazard event, and availability of contingency planning for disasters. International relief agencies (such as Oxfam and the Red Cross) have accumulated vast expertise in planning, co-ordinating and monitoring recovery activities after disasters, and they have done much to reduce indirect and long-term impacts of hazards and to reduce injury, death, hardship and suffering amongst people in hazard-prone areas.

Contingency planning

People's experience of a hazard, and the way they cope with it, reflect a variety of influences such as their perception of risk and the availability of forecasts and early warnings. The personal experience also depends on the existence of contingency plans for disaster relief, and availability of resources from within and beyond the affected area.

Co-ordination of relief activities between the various bodies involved is also very important. For example, the City of York has developed an integrated system of coping with frequent flooding by the River Ouse, such as that which occurred in December 1978. Emergency action by the City Council and County Council (Table 6) is designed to provide temporary facilities for housing and access, repair the flood damage to houses and structures, cater for the needs of flooded residents and replace chaotic reactions with a co-ordinated routine response aimed at restoring normality as soon as possible.

Table 6 City of York co-ordinated flood emergency programme

York City Council

City Engineer and Surveyors Department

provision of temporary walkways; signposting; removal of silt; filling and distribution of sandbags

Chief Environmental Health Officers Department

clearing, pumping out and drying of premises; dealing with contaminated food; drying of furniture with blow heaters in warehouses

Housing Department

assistance and advice to council tenants in flooded areas; consideration of rehousing

North Yorkshire County Council

Social Services Department

arrange temporary rehousing and feeding of displaced residents; compile list of old age pensioners and disabled people

Fire Brigade

assistance with pumping


warning residents likely to be flooded; moving people from homes; directing badly disrupted traffic flows; dissemination of information

The Army

provision of equipment; assistance with boats and personnel for evacuation

 Similar hazard coping strategies, involving co-ordination between the agencies involved, have been designed for many other areas (such as the Shrewsbury flood warning scheme) and types of hazard (such as heavy snow and blizzards in Scotland). Emergency Planning Teams have been set up by most local authorities in Britain to formulate and update contingency plans for dealing with natural hazards and possible accidents at hazardous industrial sites (like petro-chemical plants and nuclear power stations).

Contrasting hazard experiences; the case of drought

Experience of hazard events also varies between societies and cultures, because of differences in the ease with which they can adapt to hazard-induced stress. The long-term progressive onset of drought conditions, for example, poses different threats in a developed and an undeveloped country.

Pastoral, nomadic, subsistence economies - typical of the Sahel region of north Africa - are seriously affected by prolonged drought (Figure 9), which has impacts on food, livestock, human migration and human ecology. The direct impact of the drought hazard there has been magnified by people-made problems stemming from political and economic instability, land ownership and access to food and other essential resources, turning a natural hazard into a disaster of unprecedented proportions.

Figure 9. The process of breakdown of the nomadic economy in drought

Developed countries with integrated water resource management systems tend to experience drought (which is admittedly much less severe and more short-term than in the Sahel) in very different ways. Great Britain and parts of Western Europe were affected by drought (with an estimated recurrence interval of between 200 and 1,000 years) between May 1975 and August 1976. Rainfall over England and Wales in this period was only 64 percent of the long-term (1915-50) average, producing the most prolonged drought yet recorded. Inevitably this created problems in maintaining water supplies - groundwater storage was depleted, water levels in supply reservoirs fell to critical levels, some 700,000 residents in south-east Wales faced rota cuts of water supply for between seven and eleven weeks from July to September 1976.

Whilst the experience of drought in England and Wales was unwelcome, it was far from devastating. Short-term emergency measures, such as the installation of temporary water pipelines and the use of tankers for emergency supplies, increased recycling of water in production processes and voluntary water savings by industrial, business and private consumers all assisted in coping with the drought hazard and related water supply restrictions. The long period of dry weather produced other problems - agricultural crops worth an estimated 500 million were lost, there was frequent fire damage on heathland and commonland over the summer of 1976 (especially in Wales and southern England), and damage to buildings from subsidence of clays was widespread (over 50 million was paid out in response to over 20,000 claims for subsidence damage in southern England in 1976).

The experience of the 1976-76 drought in England and Wales had widespread and lasting effects of private and public attitudes to water supply and resource management (so that periods of low rainfall in the summers of 1980, 1984 and 1989 have been coped with with limited water rationing and few major water shortages), but the drought impact was relatively short-term and localised, unlike the Sahel and subsequent droughts in north Africa. In the Sahel drought people died because of lack of food and malnutrition, and were forced to migrate. In the UK no one died and no one was short of food, but daily life was subjected to considerable inconvenience.

Single and multiple hazards

It is often difficult to plan for, or cope with, hazards because relatively rarely does an event occur in isolation, and events are rarely simple. Hazards can be multiple in two ways - there may be several successive events of one hazard, or a single hazard event may be multi-dimensional in character.

Multiple events of one hazard can often occur in quick succession, making rehabilitation and reconstruction difficult and dangerous. For example, a major earthquake devastated the town of Friuli in Italy in 1976. Search and rescue operations began straight away, and within two days debris from the collapsed houses was being cleared and tents had been provided for the 60 percent of the villagers who were homeless. Emergency supplies of food were distributed over a four week period. A Reconstruction Committee, which was formed ten days after the earthquake, soon began its work and within two months a return to normality was in sight.

But a second earthquake shook the town five months after the first, making even more people homeless and setting back the reconstruction timetable considerably. Prefabricated homes were eventually provided, while permanent homes were built (which were finished some seventy weeks after the first earthquake).

Other multiple are caused by a combination of factors interacting together. A good example is the slow but continuing subsidence of the Adriatic resort of Venice. Venice has frequently been flooded by sea and river. On 4th November 1966 the flood waters reached 1.9 m above the normal water level, and this caused extensive damage to older buildings in the city and to the protective sea walls. A greater frequency of flooding in recent years has been attributed to various factors, including a general rise in sea level (in the order of 1.5 mm each year), ground subsidence (of between 5 and 10 mm per year) due to groundwater pumping, neglect of sea walls and reductions in the water storage area of lagoons by construction of dykes and infilling for development. Other factors include the lack of maintenance of many of the larger monuments, and concentration of people into the small area of the old city famous for its canals and bridges. Recent proposals to build a flood-defence barrier in Venice, similar to the Thames Barrier in London, have attracted a great deal of controversy.

Hazard ecology

Although hazard studies over the past twenty years have revealed a lot about individual hazards, we still have relatively limited understanding of the general hazard ecology of an area, taking into account all possible sources of risk and threat.

Hewitt and Burton (1971) explored the overall hazardousness of part of south-west Ontario in Canada. They found that people were exposed to thirty-one major sources of risk, which they classified into five broad groupings;

  1. including natural (such as floods and blizzards)
  2. quasi-natural (such as air and water pollution)
  3. financial (such as theft)
  4. accidental (such as fires and building collapse) and
  5. health hazards (such as hospitalisation for various reasons).

Their study showed that the local perception of these hazards placed them in quite the wrong order, so that efforts to mitigate those thought of as most serious were ill-conceived.


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Chris Park
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