The human ecology of climate change - Climate Change: Biological and Human Aspects - page 399

event. The El Ni no begins with a weakening of the prevailing winds in the Pacific and
a change in rainfall patterns that create extreme-flood and drought events in countries
surrounding the eastern Pacific and climate-related events further afield. Prolonged
dry periods may occur in south-east Asia, southern Africa and northern Australia, as
took place in 1991-2, together with heavy rainfall, and sometimes flooding in Peru
and Ecuador. During a typical El Ni no event the Asian monsoon usually weakens
and is pushed towards the equator, often bringing summer drought to north-west and
central India and heavy rainfall in the north east. The regions where the El Ni no has a
strong effect on climate are those with the least resources: southern Africa and parts
of South America and south-east Asia.
The WHO has noted that the risks of natural disasters are often highest in the years
during and immediately after the appearance of an El Nino, and lowest in the years
before. During the 1997 El Ni no central Ecuador experienced rainfall 10 times higher
than normal, which resulted in flooding, extensive erosion and mudslides with the
loss of lives, homes and food supplies. During the same El Nino there were droughts
in Malaysia, Indonesia and Brazil, exacerbating the extensive forest fires taking place
at the time. The El Ni no cycle is also associated with increased risks of disease range
(see section 7.3.2).
The El Ni no not only serves to illustrate the type of health impact an extreme
weather event may impart; the impacts themselves may change with global warming.
It has been suggested that the El Nino may become more intense and/or more frequent
with warming and so will the potential health impacts (WHO, 1999, 2001b). 2
In addition to the direct physiological effects of heat, extreme climatic events also
have indirect effects that are no less serious. A drought increases the likelihood of bush
and forest fires which are not only dangerous in themselves but destroy homes and
property, which can also have health consequences, including loss of life. For example,
in August 2003 a heatwave in Portugal resulted in the nation's worst forest fires for
20 years, killing six people. Meanwhile, at the same time Canada was experiencing
the worst fires for 50 years, which necessitated the evacuation of some 8500 people.
Consequently those concerned with the biological management of woodland are
having to come to grips with climate change and fire hazards. For example, since
1990 the western USA has seen some extreme fires that have been notable for their
size and severity. The annual US cost of fire suppression exceeded US$1.6 billion
in 2004 and the figure is rising. In the absence of large fires, much of the western
USA during the 20th century saw many forests fill with a dense understorey of shrubs
and small trees that provide so-called ladder fuels that set crowns of trees alight:
crown flares are among the most destructive of forest conflagrations. To address this
the US Healthy Forest Restoration Act (2003) determined programmes of aggressive
thinning, burning and replanting to create fire breaks and more open conditions by
removing ladder fuels (Whitlock, 2004). However, there is evidence to suggest that
this may not be appropriate as a generic strategy.
In 2004 Jennifer Pierce and colleagues from the universities of New Mexico and
Arizona published results indicating that a one-size-fits-all woodland strategy may
not be pragmatically effective. They came up with a way of looking at the long-term

2

See also discussion of the El Nino in the warmer Pliocene in section 4.3.