Decision support experiments and evaluations using seasonal to ...

The U.S. Climate Change Science Program Chapter 3
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Water managers
need help in
translating how
changes resulting
from weather
and Seasonal to
Interannual climate
variation can affect
the functioning
of the systems
they manage.
vulnerabilities of climate variability on water
resources. TOGA and RISA studies focus on
the regional scale consequences of changes to
runoff and stream flow on economies as well
as ecosystems (Milly et al., 2005).
3.2.3.1 hazardS, riSkS, and
vulnerabilitieS oF climate variability
A major purpose of decision-support tools is to
reduce the risks, hazards, and vulnerabilities
to water resources from SI climate variation,
as well as to related resource systems, by generating
climate science products and translating
these products into forms useful to water
resource managers (NRC, 2008). In general,
what water managers need help in translating
is how changes resulting from weather and SI
climate variation can affect the functioning of
the systems they manage. Numerous activities
are subject to risk, hazard, and vulnerability,
including fires, navigation, flooding, preservation
of threatened or endangered species, and
urban infrastructure. At the end of this Section,
we focus on three less visible but nonetheless
important challenges: water quality, groundwater
depletion, and energy production.
Despite their importance, hazard, risk, and
vulnerability can be confusing concepts. A
hazard is an event that is potentially damaging
to people or to things they value. Floods and
droughts are two common examples of hazards
that affect water resources. Risk indicates the
probability of a particular hazardous event occurring.
Hence, while the hazard of drought is
a concern to all water managers, drought risk
varies considerably with physical geography,
management context, infrastructure type and
condition, and many other factors so that some
water resource systems are more at-risk than
others (Stoltman et al., 2004; NRC, 1996; Wilhite,
2004).
A related concept, vulnerability, is more complex
and can cause further confusion 6 . Although
experts dispute precisely what the term means,
most agree that vulnerability considers the likelihood
of harm to people or things they value
and it entails physical as well as social dimension
(e.g., Blaikie et al., 1994; Cutter 1996;
Hewitt, 1997; Schröter et al., 2005; Handmer,
2004). Physical vulnerability relates to exposure
to harmful events, while social vulnerability entails
the factors affecting a system’s sensitivity
and capacity to respond to exposure. Moreover,
experts accept some descriptions of vulnerability
more readily than others. One commonly
accepted description considers vulnerability
to be a function of exposure, sensitivity, and
adaptive capacity (Schneider and Sarukhan,
2001). Exposure is the degree to which people
and the places or things they value, such as
their water supply, are likely to be impacted
by a hazardous event, such as a flood. The
“things they value” include not only economic
value and wealth but also cultural, spiritual,
and personal values. This concept also refers
to physical infrastructure (e.g., water pipelines
and dams) and social infrastructure (e.g., water
management associations). Valued components
include intrinsic values like water quality and
other outcomes of water supply availability such
as economic vitality.
Sensitivity is the degree to which people and the
things they value can be harmed by exposure.
Some water resource systems, for example, are
more sensitive than others when exposed to the
same hazardous event. All other factors being
equal, a water system with old infrastructure
will be more sensitive to a flood or drought than
one with new state-of-the-art infrastructure; in
a century, the newer infrastructure will be considerably
more sensitive to a hazardous event
than it is today because of aging.
6 Much of this discussion on vulnerability is modified
from Yarnal (2007). See also Polsky et al. (2007),
and Dow et al. (2007) for definitions of vulnerability,
especially in relation to water resource management.