chapter - Atmospheric and Oceanic Science

Applicability in impact assessments: They must describe changes in the adequate
variables, as well as in the spatial and temporal scales, that allows for impact
assessment. For example, several impact models can require entry data of certain
variables such as precipitation, solar radiation, temperature, humidity and wind
speed at spatial scales that may range from global to local along with time scales
varying from annual averages to daily or hourly values.
Representativity: Must be representative of the potential range of future
regional climate changes.
Accessibility: They must be straightforward to obtain, interpret and apply for
impact assessments.
12.3. Techniques for developing climate scenarios
Climate scenarios can be classified in three main types: Synthetic, analogue
and based on outputs from global climate models (GCMs).
12.3.1. Synthetic scenarios
They are built in such a way that certain climatic variables are changed in an
arbitrary but realistic amount, frequently according to a qualitative interpretation of
the climate model simulations for a region. For example, magnitudes of future
change can be represented through +1°, 2°, 3° and 4°C rise regarding the baseline
temperature, and changes in ±5, 10, 15 and 20% regarding the baseline precipitation.
The major disadvantage of the synthetic scenarios is their arbitrary nature.
Frequently they present a realistic set of changes that are physically possible, in
general representing uniform adjustments in space and time that are inconsistent
among variables. Likewise, some scenarios can be inconsistent with the range of
uncertainty of global changes. However, this limitation can be overcome when the
selection of synthetic scenarios is guided by information provided by GCMs.
12.3.2. Analogue scenarios
Climate scenarios
They are constructed by the identification of climatic regimes observed in a
certain region or period, which may resemble the future climate. These records can
be obtained both from the past of a same region (temporal analogue) or from another
region, which currently has the climate that is presumed would be at the time of
the scenario in the region of interest (spatial analogue).
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