chap2

CHAPTER TWO

SPATIAL VARIABILITY AND HUMAN PERSISTENCE

In this chapter - Spatial variability | Exposure to hazard threats | Human persistence | People-environment relationships

Hazards are naturally part of the cost of living, although some people and some areas are more at risk than others. Yet we rarely abandon places and activities which have proven to be hazard-prone.

Spatial variability

Nowhere on earth is completely safe from the threat of natural hazards. But some places are more hazardous than others (Figure 1). The danger varies from place to place, reflecting many factors (some natural, some people-made).

Figure 1. Areas at high risk from some natural hazards.

Source: Wijkman and Timberlake (1984)

Areas which have experienced hazards in the past should logically expect similar hazards to recur in the future - unless successful control measures (such as engineering schemes) have been adopted. Typical examples would include unstable hillslopes prone to landslides, low-lying floodplains and coastal areas prone to flooding, and regular storm tracks of tropical hurricanes. For example, whilst many people were surprised by the severity of Hurricane Gilbert which hit the Caribbean in November 1988, few were surprised by its location or direction.

Similarly, areas which are known to be geologically active (like fault lines, earthquake belts or volcanic zones) (Figure 1) pose greater threat than geologically unstable sites. The location of the 1985 earthquake which devastated Mexico City - on a known earthquake zone, in a location which is regularly shaken by earth tremors - was quite predictable ... even if the timing wasn't.

There is also marked spatial variability in technological hazards. Areas of greatest risk are centred on and around major industrial areas and cities, where most hazardous industrial activity and most people are concentrated. But some major technological disasters have impacts far beyond the site of the hazard event - fallout of radiation from the damaged nuclear reactor at Chernobyl was spread across Western Europe within days (Figure 2); acid rain falls hundreds of kilometres downwind from the power stations and cities which are the main emission sources of sulphur dioxide and nitrogen oxides.

Figure 2. Spread of radiation across Europe after the nuclear accident at Chernobyl.

Source: Park (1989)

Exposure to hazard threats

A striking example of irrational human behaviour is the way we often expose ourselves - sometimes consciously - to risk.

One of the classic examples must be San Francisco. The city is built astride the San Andreas Fault, which marks the point of contact between two crustal plates - the Pacific Plate (to the west) and the American Plate (to the east). Geological evidence has shown that the Pacific Plate is gliding northwards at a rate of about 60 m per year, although a pattern of stick and slip means that periodically earthquakes occur. The largest recent earthquake occurred at 5.12 am on the 18th April 1906. The violent movement (8.25 on the Richter scale) produced visible faulting, an upthrow of some 2 m on the east side of the fault, and lateral displacement of nearly 4 m. An estimated 700 people died, mostly through fires started by broken gas mains, which spread rapidly through San Francisco's wooden buildings. Attempts to dampen the raging fires were hampered by ruptured water supply pipes. Damage was estimated at between $350 and $1,000 million (at 1906 prices).

San Francisco has since been affected by several earthquakes, such as that of the 22nd March 1957. This fairly strong movement (5.3 Richter) did not produce surface faulting, no lives were lost directly, and few buildings were damaged. The November 1989 earthquake also caused deaths, injuries and extensive damage to property and services. But despite the known hazard risk, city residents show a marked reluctance to alter patterns of behaviour. Many highways and buildings (including, somewhat ironically, schools and hospitals) are built across the high risk fault zone. Predictions of up to 50,000 deaths and $50,000 million of damage from the next major earthquake have little impact on investors, land owners and residents. They are aware of the hazard, but the economic attractions of the city and our ability to set risk on one side means that little is done about it. Regulations require that new buildings are able to resist earthquake vibration, but the older stock is highly likely to collapse when the next 'big one' occurs, as happened in the Fisherman's Wharf area in the 1989 earthquake.

Human persistence

Logically, people should avoid high risk areas. If they live there, they should move away. But there are various reasons why we are not so rational.

(a) Unpredictability

Environmental hazards are not entirely predictable. We cannot usually be certain where and when a hazard event is likely to occur, even though it is logical to expect that one will! For example, few people doubt that San Francisco will not be exposed to a major earthquake - as big if not bigger than the devastating one of 1906 - some time in the future. The unknown questions are "when, and how big?".

(b) Lack of alternatives

Quite often people have few alternatives to continuing to live and work in a hazardous place. They simply cannot uproot home and family and move elsewhere with no prospect of housing, jobs or security. This is particularly so in developing countries, where many people stay even after major disasters have devastated an area. People in many developing countries (such as along the floodplains in Bangladesh) have temporary evacuation strategies, but they return to the hazardous sites when the waters have receded because of lack of suitable alternative land to work. A host of factors tie people to an area (even an unsafe area). Some are cultural; tribal roots, ancestral ties and even myths and fables root people in traditional places. Others are economic; farmers cannot abandon their livelihood and move elsewhere, and employment links - the only income for most people - cannot be severed without the promise of viable alternatives elsewhere. Yet others are educational (people are often not fully aware of all the alternatives open to them), or personality dependent (where, for example, inertia and fear of change are powerful influences).

(c) Changing dangers

The nature of hazard risk often changes through time, so that places which in the past might have been regarded as safe may not always remain so. For instance, low-lying coastal areas may in the future be threatened with flooding if air pollution promotes global warming and a rise in sea-level. If that happened, many of the world's major cities (such as London, Tokyo and New York) and industrial areas (such as much of Japan and east coast United States) would be at considerable risk.

(d) Russian Roulette

We have a natural habit of turning a blind eye to known risks and threats. It seems to be part of human nature to think that "things are not so bad after all", or that "lightning never strikes twice in the same place". As a result, we often seem to accept regular hazard losses, damage and disruption as simply part of the cost of living.

(e) Costs versus benefits

Some places and some environments, which are known to be hazardous, offer benefits which seem to outweigh the risks involved. For instance, volcanic areas offer rich fertile soils and valuable farming land in many tropical areas, where rapid leaching tends to remove plant nutrients from the soil. Ironically, the very existence of these resources encourages people to settle in the hazardous areas. In Indonesia, for example, there is a close link between amount of volcanic activity and density of rural population. The attraction of the rich agricultural soils makes people take up the risk of living under the shadow of the volcanoes.

Other examples of weighing up advantages and disadvantages of hazardous sites include river floodplains (where benefits like water supply, access, gravel for building and flat sites must be offset against risks of flooding, channel changes and overbank deposition of sediment), and coastal cliff-top sites with panoramic sea views prized for holiday and retirement homes, but which are also open to wave- and storm-attack and cliff collapse.

People-environment relationships

The constant interplay between people and their environment is a two-way association (symbiosis) based on opportunities and constraints. Opportunities arise from the resources (like land, water and food) which the environment offers for human development; constraints arise from hazards which limit the exploitation of resources (Figure 3).

Figure 3. The symbiosis between people and environment

Hazards are, by definition, bad news. They kill and injure people, disturb communities and destroy property. But there is some good news, because the very environmental processes which give rise to the hazards also perform services which are valuable to mankind. Few popular holiday beaches would have sand if it were not for periodic river floods which flush sediment from upstream areas. Floods also help to disperse pollutants along rivers and estuaries ("dilution is the solution to pollution") and they provide valuable nutrients to floodplains (such as the Nile before the Aswan Dam was built) as well as watering vast grazing lands in semi-arid areas, causing plants to flourish. Volcanoes create new land and provide nutrient-rich ash; earthquakes create mountains which are prized as scenic resources. In many other situations the benefits and drawbacks of natural environmental processes must be carefully weighed side-by-side.