Environmental Engineering Reference
In-Depth Information
phenomena'. Historically, the rate of spread of communicable diseases has
wholly depended on the growth and concentration of human populations.
The unprecedented population densities in 14th century Europe led to the
plague outbreak that wiped out a quarter of the population.
Around 40 per cent of people now live in cities of over a million people,
a function of rural-urban migration and population growth. Overcrowding,
or the increased proximity of susceptible individuals, favours the spread of
infectious diseases such as tuberculosis, dengue fever, malaria and acute res-
piratory illnesses. In addition, the kind of rapid urbanisation as seen in
developing countries is often characterised by a lack of clean water and poor
sanitation, leading to water-borne diseases such as cholera and diarrhoea.
Disease vectors, such as mosquitoes and rats, thrive in such cities, further
facilitating the spread of disease (Brown
et al.
1999).
Degradation of the global environment as a result of population
numbers quadrupling and economic activity increasing twentyfold over the
past century, however, has the gravest implications for health. As McMichael
notes, it has changed the conditions of life on Earth 'by altering global cli-
mate, depleting stratospheric ozone, extinguishing whole species and their
local populations and damaging food producing ecosystems on land and at
sea'. The effects are felt mostly at local and national levels.
Global climate change has contributed to an increase in natural disasters
over the last three decades of the 20th century. One billion or so people suf-
fered from them, mainly in poorer countries (McGuire 2002). Developing
countries are particularly susceptible to disasters such as mudslides, cyclones
and flooding because rapid population growth has meant that people
increasingly utilise high risk terrains such as steep hillsides, flood-plains and
coastal zones for habitation and farming. Many developing countries are
also in the tropics and these areas experience higher rates of natural disasters
than temperate countries.
Land use and natural ecosystems
John Williams and Denis Saunders (Chapter 5) note that current land use in
Australia is unsustainable. It is characterised by extensive loss of species,
changes in ecosystem processes and increasing degradation of land and
water resources. Much of the degradation is a result of extensive land clear-
ing and replacement of long-rooted native perennials with short-rooted
annuals. This causes watertables to rise, bringing salts to the surface.
