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Determining the Local Implications of Global Warming

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To understand the impact of global warming on the Northwest, one starts with ... But GCMs can only describe features a thousand or more km in scale. ... – PowerPoint PPT presentation

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Title: Determining the Local Implications of Global Warming


1
Determining the Local Implications of Global
Warming
Professor Clifford Mass, Eric Salathe, Patrick
Zahn, Richard Steed University of Washington
2
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?

3
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.

4
Local Northwest Weather Terrain Water
Influence
5
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.

6
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

7
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

8
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.

9
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10
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.

11
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.

12
Forecast Model Nesting
  • 135, 45, 15 km MM5 domains
  • Need 15 km grid spacing to model local weather
    features.

13
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

14
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
15
Global Forcing Surface Temperature
16
ECHAM Global Climate System Model
17
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.

18
Next Presentation
  • Patrick Zahn will tell you how we did it.

19
The END
20
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21
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…

22
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23
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24
1990 Equivalent Snow Depth
25
2021 Equivalent Snow Depth
26
2045 Equivalent Snow Depth
27
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28
More Surprises?
  • Example More thunderstorms in summer, helping
    alleviate water problems--but causing more fires?

29
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.
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