Geoscience Reference
In-Depth Information
Probable Direction
Extreme Event
Throughout 21st Century
Likelihood
Note: > 50% is
used when the
likelihood can be
estimated with
reasonable good
precision, and
33 to 66% is used
when there is not
high confidence
in the likelihood
estimate.
Intense hurricanes
More likely than not
Nor'easters
Unknown
Extreme winds
More likely than not
These definitions of likelihood are used by the IPCC (2007) to describe potential outcomes.
>99%
Virtually certain
>66%
Likely
>95%
Extremely likely >50%
More likely than not
>90%
Very likely
33 to 66% About as likely as not
Figure 8 Continued.
Although these modeling tools were initially developed to answer questions about
possible infrastructure implications of terrorist actions, they have been widely used to
provide decision support during weather and other emergencies. As disruptions such
as Hurricane Irene and the San Diego blackout emerge, infrastructure interdependency
models are used to help anticipate and deal with cascading infrastructure effects. A co-
benefit has been that interdependencies predicted by the models can, in each case, be
compared with observed interdependencies; and the models can be refined to close the
gap between predictions and real-world effects. Rarely have there been such rich oppor-
tunities to connect model development with observations, and a result has been signifi-
cant improvement in the accuracy of the model depictions of interdependencies over the
past half-dozen years.
One approach for representing interactions between systems and the population,
developed to answer national security questions, is illustrated by Figure 9 . For example,
there will be multiple factors influencing the risks to electric power supply within a re-
gion. There will be changes in demand for electric power, including peaks, averages and
variability in demand, due to:
• Changes in temperatures and their impact on demand (residential heating,
cooling, industrial and commercial)
• Changing economic conditions
• Population relocation
Moreover, changes in electric power transmission are possible if:
• Transmission capacities are reduced due to high temperatures and/or
• New transmission capacity utilization paterns emerge due to changes in
demand
In order to evaluate all of these risks, it is necessary to estimate the probability of each
change and the capacity of the existing infrastructure to adjust to the potential perturba-
tions. For instance, changes in the distribution of population and economic activity will
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