CDF data: In detail
- What
should I use them for?
-
Preparing maps and graphs
CDF data are used to form the CDF and PDF graphs, and plume plots
available from the UKCP09
User Interface (external website). Maps available within UKCP09
(publications, maps, and within the
User Interface) are derived using values for a specified probability
level from the CDF data for every 25 km grid square
for a given 30-year time period, temporal average,
and associated emissions scenario.
Users can also download the CDF data (comma-separated format) and
use
it to prepare other required images using their own graphics
packages.
-
Exploring the nature of the projections relative to single variable
thresholds
Using either the CDF data itself or any of the maps, graphs and
plots available from the UKCP09 User Interface users can explore the
nature of the projected climate as reflected by a single variable,
especially with respect to specific thresholds and
levels of acceptable risks. This type of scoping exercise can be quite
useful as a means of defining the need for, and specific nature of, more
detailed assessments (e.g. which part of the probabilistic
projections to focus attention on within the assessment).
There may also be some benefit to using the CDF data and images to
identify other areas of interest where more detailed assessment may be
warranted. This could arise where a detailed location-specific study
(for one 25 km grid-square
or aggregated area)
has identified a level of risk requiring attention and you are
interested in identifying if other locations of interest would also
warrant a detailed assessment.
Users should be aware that the CDF data only provides information
for one variable for one location (25 km grid square and aggregated
areas), one 30-year time period, one temporal average and under one
emissions scenario. This also means that users should take care when
interpreting any of the maps derived using this data as they are
presentations of changes (or absolute climate) at a given probability
level rather than a presentation of the projected change as was the case
in UKCIP02 (see Interpreting customisable maps
section).
- Input into impacts models that only require one
variable
In the case where an impacts model or risk assessment only requires
the input of one climate variable, CDF data can be used. When there is a
need for a more detailed assessment that includes more than one climate
variable then the UKCP09 sampled data will need to be used.
Users should be aware that the CDF data only provides information
for one variable for one location (25 km grid square and aggregated
areas), one 30-year time period, one temporal average and under one
emissions scenario.
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- CDF data should not be used where information on
more than one variable is required
Most risk, impacts and adaptation assessments
require information on more than one variable, including
the capturing of how these variables depend on each other. The CDF data
is a single variable data set and therefore does not include these
dependencies.
As the UKCP09 sampled data does
capture the dependence among multiple variables (within a specific batch), this data
should be used in these cases instead. If there is a key variable and
associated threshold of
interest, the CDF data can be explored to aid in selecting the sampled
data required for further analysis within the assessment process.
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The CDF data considers the uncertainties
used throughout UKCP09
(see Chapter
3 of the Climate change projections report).
Emission uncertainty is explored through the use of three sets of
CDF
data each developed using one of the three UKCP09 emission scenarios :
- Low emissions scenario (IPCC SRES B1)
- Medium emissions scenario (IPCC SRES A1B)
- High emissions scenario (IPCC SRES A1FI)
A single CDF data file provides probability levels
associated with a single, user-specified emissions scenario.
Multiple
CDF data files will need to be integrated to explore the
implications
of emission uncertainties for the results (risk, impacts and adaptation assessments).
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