9.5.2. Storms and Tropical Cyclones
Impoverished and high-density populations in low-lying and environmentally
degraded areas are particularly vulnerable to tropical cyclones (also called
hurricanes and typhoons). Many of the most serious impacts of tropical cyclones
in the 20th century have occurred in Bangladesh because of the combination of
meteorological and topographical conditions, along with the inherent vulnerability
of this low-income, poorly resourced population. Tropical cyclones also can
cause landslides and flooding. Most deaths are caused by drowning in the storm
surge (Alexander, 1993; Noji, 1997). The impacts of cyclones in Japan and other
developed countries have been decreasing in recent years because of improved
early warning systems. However, the experience of Hurricane Mitch demonstrated
the destructive power of an extreme event on a densely populated and poorly
resourced region (PAHO, 1999).
9.5.3. Droughts
The health impacts of drought on populations occur primarily via impacts on
food production. Famine often occurs when a preexisting situation of malnutrition
worsens. The health consequences of drought include diseases resulting from
malnutrition (McMichael et al., 1996b). In times of shortage, water is
used for cooking rather than hygiene. In particular, this increases the risk
of diarrheal diseases (as a result of fecal contamination) and water-washed
diseases (e.g., trachoma, scabies). Outbreaks of malaria can occur during droughts
as a result of changes in vector breeding sites (Bouma and van der Kaay, 1996).
Malnutrition also increases susceptibility to infection.
In addition to adverse environmental conditions, political, environmental,
or economic crises can trigger a collapse in food marketing systems. These factors
may have a cumulative or synergistic effect. For example, a breakdown in the
reserve food supply system resulting from the sale of grain or livestock reserves
might be exacerbated by conflict and breakdown in law and order. The major food
emergency in Sudan during 1998 illustrates the interrelationship between climatic
triggers of famine and conflict. Land mines made portions of major roads in
southern Sudan impassable and contributed to poor access for relief supplies.
By July 1998, the World Food Programme's air cargo capacity had increased to
more than 10,000 t to overcome the transport difficulties. These air cargoes
were supplemented by barge convoys and road repair projects (WFP, 1999). Vulnerability
to drought and food shortages can be greatly reduced through the use of seasonal
forecasts as part of an early warning system (see Section
9.11.1).
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Box 9-1. Stratospheric Ozone Depletion and Exposure to Ultraviolet
Radiation
Stratospheric ozone destruction is an essentially separate
process from greenhouse gas (GHG) accumulation in the lower atmosphere.
However, not only are several of the anthropogenic GHGs [e.g., chlorofluorocarbons
(CFCs) and N2O] also ozone-depleting gases but tropospheric
warming apparently induces stratospheric cooling, which exacerbates
ozone destruction (Shindell et al., 1998; Kirk-Davidoff et
al., 1999). Stratospheric ozone shields the Earth's surface
from incoming solar ultraviolet radiation (UVR), which has harmful effects
on human health. Long-term decreases in summertime ozone over New Zealand
have been associated with significant increases in ground-level UVR,
particularly in the DNA-damaging waveband (McKenzie et al., 1999).
In a warmer world, patterns of personal exposure to solar radiation
(e.g., sunbathing in temperate climates) also are likely to change.
Many epidemiological studies have implicated solar radiation
as a cause of skin cancer (melanoma and other types) in fair-skinned
humans (IARC, 1992; WHO, 1994). The most recent assessment by UNEP (1998)
projects significant increases in skin cancer incidence as a result
of stratospheric ozone depletion. High-intensity UVR also damages the
eye's outer tissue, causing "snowblindness"—the
ocular equivalent of sunburn. Chronic exposure to UVR is linked to conditions
such as pterygium (WHO, 1994). The role of UV-B in cataract formation
is complex. Some cataract subtypes appear to be associated with UVR
exposure, whereas others do not. In humans and experimental animals,
UVR can cause local and whole-body immunosuppression (UNEP, 1998). Cellular
immunity has been shown to be affected by ambient doses of UVR (Garssen
et al., 1998). Concern exists that UVR-induced immunosuppression
could influence patterns of infectious disease. Nevertheless, no direct
evidence exists for such effects in humans, and uncertainties remain
about the underlying biological processes.
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