Options for Improving Climate Modeling to Assist Water Utility ...

Water Utility Climate Alliance White Paper
Options for Improving Climate Modeling to Assist Water Utility Planning for Climate Change
design consists of seven simulation regions around the globe. Each RCM was best configured for
simulation of climate in its native developmental region and then was applied in one of the other
six simulation regions without reconfiguration.
Likewise, comparison of statistical downscaling techniques has been pursued more vigorously in
Europe than in the United States. Most intercomparisons are performed in support of specific
project objections and involve evaluation of a small number of statistical downscaling techniques
for a particular region for a couple of variables. By comparison, the Statistical and Regional
Dynamical Downscaling of Extremes for European regions (STARDEX) is the most
comprehensive intercomparison of statistical downscaling techniques to date and includes over
20 statistical downscaling approaches applied in multiple regions of Europe to a standard set of
variables.
The success of statistical and dynamic downscaling intercomparison projects worldwide, even
though few in number, has prompted an internationally coordinated intercomparison project
under the auspices of a working group within the World Meteorology Organization’s World
Climate Research Programme. The project, the COoperative REgional Downscaling EXperiment
(COREDEX), is comprised of experts in both RCMs and statistical downscaling methods.
COREDEX will provide guidance on experimental design considerations, such as domain
location and size, grid spacing, and data archive requirements. Although in its early stages,
COREDEX has developed target domains focusing primarily on developing countries, though all
continents are covered. The simulation period is expected to be 19502070 with RCMs no
coarser than 0.5 (about 50 km). The relatively coarse minimum RCM resolution is needed to
accommodate the technological capacity of developing nations. The experiments expect to make
use of at least five CMIP5 global climate simulations as they become available over the next two
to four years, and will include RCP 4.5 and 8.5 scenarios. Additionally, a baseline climate
simulation will be included that will span 19872009.
3.2.8 What results have the climate downscaling evaluation efforts produced?
The key result from evaluations of RCM versus statistical downscaling techniques is that they
have comparable skill overall. However, an important idea that has not been evaluated widely is
that some of the limitations of statistical and dynamical downscaling techniques may be
overcome by using them in tandem. Running dynamical downscaling first and then applying
statistical downscaling to the outputs from the mechanistic modeling may allow for simulations
of both the station data and feedback of regional processes into the large-scale circulation. Such
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