2.3.5.1. Developing Scenarios of Changes in Variability and Extreme Events
Working Group I discusses methodologies for estimating changes in variability
from the results of GCMs (see Sections 9.3.2 and 13.4.2).
Despite certain shortcomings, GCMs can provide estimates of trends in climatic
variability. Using extreme events from historical data as analogs also is useful.
The frequency of extreme events is likely to change as mean values shift, even
without changes in variability. Chapter 3 reviews potential
changes in different climatic elements (see Table 3-10).
From the instrumental record, some regional changes in extremes have been identified,
although it is difficult to say whether they are related to GHG-induced climate
change. For example, there has been a recent increase in heavy and extreme precipitation
in the mid to high-latitude countries of the northern hemisphere, and in several
regions of east Asia a decrease in the frequency of temperature extremes together
with heavy and extreme precipitation have been observed (see TAR
WGI Chapter 2)
2.3.5.2. Estimating First-Order Impacts
Many models that validate well for present climate conditions may not respond
realistically to future climatic conditions and subsequent changes in extreme
events. For some sectoral impacts, however, methods for evaluating a system's
response to changes in variability change are improving. One example is estimation
of changes in flooding by using 10-year return periods given by transient GCMs
and applied to a watershed model (Takahashi et al., 1998).
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