Human exposure to environmental threats is not evenly distributed. Some
locations, such as high latitudes (see box below), floodplains, river
banks, small islands and coastal areas, may pose more risk than others.
Human uses or modifications of the environment such as deforestation,
increasing paved areas covered by buildings and roads, and river canalization
have created impacts that often affect areas a long way from the source
of the environmental change, such as far downstream.
|The hazards of living in high latitudes
|People living in high latitudes are particularly vulnerable to malignant
melanoma (skin cancer). The prevalence of this condition has increased
dramatically in the 20th century and has been attributed to increased
ultraviolet (UV) radiation resulting from ozone depletion, caused
mainly by industrialized countries. Changes in behaviour, such as
increasingly outdoor lifestyles and sunbathing, are contributory factors.
In the year 2000, 78.5 per cent of melanoma cases, and 73 per cent
of melanoma-related deaths reported worldwide, were in developed countries
(Ferlay and others 2001). In the United States, there has been a 1
800 per cent rise in reported cases of malignant melanoma since 1930.
One in five Americans develops skin cancer, and one American dies
of it every hour (US EPA 1998).
Individual choices have an enormous bearing on where people live and
work, with the result that human vulnerability is closely related to population
density and distribution. Floodplains, low-lying coastal areas and volcanic
areas have always been favoured for settlement because of their soil fertility
or the availability of flat land. As populations increase and there is
more competition for land and resources, areas of higher potential risk
are increasingly being settled, such as mountains, steep slopes and locations
near sources of pollution. Such settlers are vulnerable to the associated
single or combined hazards such as landslides, flooding, volcanic eruptions
and toxic chemicals. Again, the poorest strata of society are often the
most vulnerable because they have fewer options in where to live.
For various reasons, even the more affluent often choose to live or work
in areas prone to environmental threats or hazards. Those living along
the earthquakeprone San Andreas fault in California are a prime example,
as are those who settle in hurricane belts, on sand spits, on eroding
coastlines or in towns where water supplies are inadequate to meet demand.
Clearly, the benefits of the location (employment, job security, leisure
facilities) are perceived to outweigh the known risks. Measures to mitigate
the risks may be sought in the form of insurance or purchasing a scarce
commodity such as water but these options are not always appropriate,
available or affordable to all members of the community.
|Floods caused by glacial lake outbursts
Glacial lake outburst floods (GLOFs) are catastrophic discharges
of water resulting primarily from melting glaciers.
Global warming over the past half century has led to an accelerated
retreat of the glaciers and enlargement of several glacial lakes
in the Hindu Kush and Tibetan Himalayas. In Bhutan, for example,
some glaciers are retreating at a rate of 20-30 metres a year. Many
glacial lakes are dammed by unstable moraines. Occasionally these
dams burst and release large amounts of stored water, causing serious
flooding downstream and along the river channel. The water contains
substantial debris and causes serious damage - often at great distances
from the outburst source; in Pakistan, damage has occurred 1 300
km from the outburst source. Such flash floods are a common problem
in countries such as Bhutan, China (Tibet), India, Nepal and Pakistan.
In Nepal, records indicate that GLOFs occur once every three to
ten years. Over the past few decades at least 12 GLOFs have caused
major damage to infrastructure. For example, Dig Tsho glacial lake
in Bhutan burst on 4 August 1985, causing significant loss of life
and destroying the nearly completed Namche hydropower plant, as
well as 14 bridges.
|Sources: WECS 1987, Watanabe and Rothacher 1996
In 2002, more than 1 billion urban dwellers, mostly in Africa, Asia and
Latin America, live in slums or as squatters UNCHS 2001). Of the projected
1 billion new urban dwellers by 2010, most will probably be absorbed by
cities in developing countries that already face multiple problems such
as shortages of adequate housing, infrastructure, potable water supplies,
adequate sanitation and transportation systems as well as environmental
pollution. The urban poor, unable to afford alternatives, are frequently
forced to live in areas with the worst urban services and most unhealthy
environmental conditions, exposed to multiple hazards and increased risk,
their vulnerability enhanced by overcrowding.
Some communities have become more vulnerable because the scarcity of
critical resources such as land, fresh water and forests is contributing
to conflicts. These environmental scarcities do not usually cause wars
among countries but they can generate severe social stresses within countries
or across borders, helping to stimulate sub-national insurgencies, ethnic
clashes and urban unrest. Such civil violence affects developing societies
particularly because they are generally more dependent on environmental
resources and less able to buffer themselves from the social crisis that
environmental scarcities cause (Homer- Dixon 1999).
|Africa's Lake Victoria basin: multiple dimensions
An estimated 30 million people depend on Lake Victoria, a lake
whose natural resources are under increasing stress. The population
on the shore has grown fast over the past century with corresponding
increases in the demand for fish and agricultural products. Following
the introduction of gill nets by European settlers at the beginning
of the 20th century, populations of indigenous fish species declined.
Many were specially adapted to eat algae, decaying plant material,
and snails that host the larvae of Schistosomes that cause bilharzia
in humans. The lake started to eutrophicate and people became more
vulnerable to disease.
As fish catches declined, non-native species were introduced, so
causing further stress to indigenous fish. The greatest impact resulted
from the introduction of nile perch (Lates niloticus) in
the 1960s, as the basis of commercial freshwater fisheries. This
had repercussions on the local fishing economy and distribution
of wealth. Local people who previously met most of their protein
requirements from the lake began to suffer from malnutrition and
protein deficiency. Although 20 000 tonnes of fish are exported
annually to European and Asian markets, local people can afford
only fish heads and bones from which the flesh has been removed.
Wetlands around the lake have been converted to grow rice, cotton
and sugarcane, and their function as natural filters for silt and
nutrients has been lost. Run-off now carries soil and excess nutrients
from the cultivated areas straight into the lake. The resulting
algal growth clouds the surface water and reduces oxygen availability,
seriously affecting the habitat of endemic fish species, which prefer
clear waters, while their predator, the nile perch, thrives in such
murky waters. This further aggravates food insecurity in lakeside
Increased nutrients, much in the form of sewage, have stimulated
the growth of the water hyacinth (Eichornia crassipes), one
of the world's most invasive plants. This has seriously affected
water transport and paralysed many local fisheries. By the end of
1997, the 70 per cent decline in economic activity reported at Kisumu
port was attributable to water hyacinth choking the port and fish
landings. The dense cover of water hyacinth also stimulated secondary
weed growth, and provided habitats for snails and mosquitoes - this
in an area where the incidence of bilharzia and malaria is already
among the highest in the world.
|Source: Fuggle 2001