Determining the Local Implications of Global Warming

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Determining the Local Implications of Global
Warming
Professor Clifford Mass, Eric Salathe, Patrick
Zahn, Richard Steed University of Washington
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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?

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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.

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Local Northwest Weather Terrain Water
Influence
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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.

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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

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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

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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.

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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.

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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.

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Forecast Model Nesting

• 135, 45, 15 km MM5 domains
• Need 15 km grid spacing to model local weather
  features.

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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

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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
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Global Forcing Surface Temperature
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ECHAM Global Climate System Model
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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.

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Next Presentation

• Patrick Zahn will tell you how we did it.

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The END
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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

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1990 Equivalent Snow Depth
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2021 Equivalent Snow Depth
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2045 Equivalent Snow Depth
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More Surprises?

• Example More thunderstorms in summer, helping
  alleviate water problems--but causing more fires?

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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.