Transcript Regional High Resolution Prediction

Determining the Local
Implications of Global Warming
Professor Clifford Mass, Eric Salathe,
Patrick Zahn, Richard Steed
University of Washington
Questions
What are the implications of global
warming for the Northwest?
How will our mountains and land-water
contrasts alter the story?
Are we going to simply warm up or are
there some potential surprises?
Regional Climate Prediction
• To understand the impact of global warming on
the Northwest, one starts with global
circulation models (GCMs) that provide a view
of the large-scale flow of the atmosphere. But
GCMs can only describe features a thousand or
more km in scale.
• HOWEVER, Northwest weather is dominated
by terrain and land-water contrasts and in order
to understand the implications of global
changes on our weather, local downscaling of
the GCM predictions is required.
Local Northwest Weather =
Terrain + Water Influence
Downscaling and Surprises
• The traditional approach to use GCM
output is through statistical downscaling,
which finds the statistical relationship
between large-scale atmospheric structures
and local weather.
• Statistical downscaling either assumes that
current relationships will hold or makes
simplifying assumptions on how local
weather works.
Downscaling
• Such statistical approaches may be a good start,
but may give deceptive or wrong answers…
there may in fact be “surprises” produced by
local terrain and land/water contrasts.
• In other words, the relationships between the
large scale atmospheric flow and local weather
might change in the future
Downscaling
• There is only one way to do this
right… running full weather
forecasting models at high resolution
over extended periods, with the large
scale conditions being provided by the
GCMs….called dynamical
downscaling.
• Such weather prediction models have
all the physics, so they are capable of
handling any “surprises”
Example of a Potential Surprise
• Might western Washington be colder during
the summer under global warming?
– Reason: interior heats up, pressure falls,
marine air pushes in from the ocean
• Might the summers be wetter?
– Why? More thunderstorms due to greater
surface heating.
Downscaling
• Computer power and modeling
approaches are now powerful enough
to make dynamical downscaling
realistic… and this and the next two
talks will describe work at the UW that
follows this approach.
• Takes advantage of the decade-long
work at the UW to optimize weather
prediction for our region.
UW Regional Climate Simulations
• Makes use of the same weather prediction
model that we have optimized for local
weather prediction: the MM5.
• 10-year MM5 model runs nested in the
German GCM (ECHAM).
• MM5 nests at 135km, 45km, and 15 km
model grid spacing.
Forecast Model Nesting
• 135, 45, 15 km MM5 domains
• Need 15 km grid spacing to model local weather features.
Regional Modeling
• Ran this configuration over several
ten-year periods:
• 1990-2000-to see how well the
system is working
• 2020-2030 and 2045-2055 (4 years
so far) to view the future
Details on Current Study: GCM
• Parallel Climate Model (DOE -PCM) output provide
by NCAR and European ECHAM model
• Horizontal resolution ~ 150km.
• IPCC climate change scenario A2 -- aggressive CO2
increase (doubling by 2050)
IPCC Report, 2001
IPCC Report, 2001
Global Forcing: Surface Temperature
ECHAM Global Climate System Model
First things first
• But to make this project a reality we needed
to conquer some significant technical
hurtles.
• We also had to understand the biases in our
coupled modeling system….so we know
what is climate change and what is model
bias.
Next Presentation
• Patrick Zahn will tell you how we did it.
The END
UW Regional Climate Study
• We have completed the first series of
simulations, having overcome a number of
technical challenges.
• Some early views of the results…
1990 Equivalent Snow Depth
2021 Equivalent Snow Depth
2045 Equivalent Snow Depth
More Surprises?
Example: More thunderstorms in
summer, helping alleviate water
problems--but causing more fires?
Future
• We are now rerunning the regional simulations
with better GCM output (ECHAM model)
• Should be done in roughly 1-2 months
• Will use this model output to evaluate water
resources and air quality.
• Will try other global warming scenarios.