Climate change futures: health, ecological and economic dimensions

CASE STUDIES 88 | NATURAL AND MANAGED SYSTEMS
HEALTH AND ECOLOGICAL IMPACTS
Access to safe, adequate drinking water is considered
a primary driver of public health. The World Health
Organization estimates that 80% of worldwide disease
is attributable to unsafe water or insufficient sanitation
(WHO, in Cooper 1997). Waterborne diarrheal diseases
are the primary causes of water-related health
problems.
Warmer temperatures can lead to increased microbial
and algal growth in water sources. Studies have
linked yearly outbreaks of gastroenteritis among children
in Harare, Zimbabwe, to seasonal freshwater
algal blooms with cyanobacteria (blue-green algae) in
the reservoir that supplies their neighborhoods with
water (Chorus and Bartram 1999; Zilberg 1966). In
Bahia, Brazil, a 1988 outbreak of gastroenteritis that
killed 88 people living near the Itaparica Dam was
linked to a large bloom of cyanobacteria in the
dammed lake (Chorus and Bartram 1999; Teixera et
al. 1993).
As increased temperatures and decreased precipitation
lead to a decrease in water volume of surface
sources, the concentration of contaminants such as
heavy metals and sediments will increase (McCarthy et
al. 2001; Levin et al. 2002). For example, Lake
Powell, in Utah, covers 160,000 acres when full, but
has lost 60% of its volume in recent droughts. As the
water level drops, agricultural chemicals that have
been collecting on the lake's bottom since its creation
may begin to mix with water traveling through the dam
at the base of the lake. This could result in contamination
of the Grand Canyon, which lies about 75 km
downstream (Johnson and Murphy 2004).
Precipitation plays a large role in waterborne-disease
outbreaks. Heavy rainfall can wash microbes into
source waters in large quantities, in addition to causing
combined sewers to overflow. Microbes are also
transported much more easily through saturated soil
than through dry soils (Rose et al. 2001). Many studies
demonstrate a correlation between heavy rainfall
and outbreaks of waterborne diseases, including cryptosporidiosis,
giardiasis and cyclosporidiosis (Checkley
et al. 2000; Speelmon et al. 2000; Curriero et al.
2001; Rose et al. 2000; Casman et al. 2001).
Between 1948 and 1994, 68% of all waterborne-disease
outbreaks in the US occurred after rainfall events
that ranked in the top 20% of all precipitation events
by the amount of water they deposited (Curriero
2001). These outbreaks showed a distinct seasonality,
becoming more frequent in summer months, and
cyclosporidiosis incidence in Peru was found to peak
during the summer as well, suggesting that temperature
also plays a role in WBDO patterns (Rose et al. 2001).
During the El Niño event of 1997-1998, with mean
temperatures 3.4°C higher than the average of the
previous five summers, reported cases of both cholera
(Speelmon et al. 2000) and childhood diarrhea
(Checkley et al. 2000) in Lima, Peru, increased significantly.
The growth of Vibrio cholerae (the pathogen
that causes cholera) and other pathogens responsible
for diarrheal diseases accelerates in warm conditions.
The growth of microbial slime in biofilms in water distribution
systems is also sensitive to temperature, and it
is likely that microbes in biofilms acquire resistance to
disinfectants at high rates (Ford 2002).
Due to underreporting of diarrheal illnesses, the prevalence
of waterborne diseases may be much higher
than is currently believed (Rose et al. 2001). For the
general population, these waterborne diseases are not
usually serious, but they can be fatal if water, sugars,
and salts are not replaced. For example, the mortality
rate for untreated cholera is approximately 50%, while
the mortality rate for properly treated cholera is 1%.
Vulnerable populations, such as immunocompromised
people (those with weakened immune systems) —
including infants, the elderly and pregnant women —
are more susceptible to waterborne diseases. Among
AIDS patients in Brazil, cryptosporidiosis was the most
common cause of diarrhea (Wuhib et al. 1994), and
85% of the deaths following a cryptosporidiosis outbreak
in Milwaukee, WI, in 1993 occurred in those
with HIV/AIDS (Hoxie et al. 1997).
ECONOMIC DIMENSIONS
Based on the midrange 1996 IPCC projections for doubling
of CO 2
(2.5°C, or 4.5°F), Hurd et al. (1999)
project US losses from such parameters as water-quality
changes, hydroelectric power losses, and altered agriculture
and personal consumption to be US $9.4 billion.
With a 5°C rise in global temperatures, without
changes in precipitation, the estimates rise to US $31
billion for water-quality impacts out of a total of US $43
billion damage. These estimates, it should be noted, do
not take into account variance and the increasing frequency
of heavy and very heavy rain events accompanying
warming (Groisman et al. 2004).