University of Washington experimental westwide seasonal hydrologic forecast system

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University of Washington experimental west-wide
seasonal hydrologic forecast system

• Andrew W. Wood
• Dennis P. Lettenmaier
• Department of Civil and Environmental Engineering
• University of Washington
• for presentation at
• Climate Prediction Applications Science Workshop
• International Research Institute
• Palisades, NY
• March 17, 2005

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Forecast System Overview
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Forecast System Schematic
experimental, not yet in real-time product
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Modeling Framework
Snowpack Initial Condition
Soil Moisture Initial Condition
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Forecast points and sample streamflow forecasts
monthly hydrographs
targeted statistics
e.g., runoff volumes
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Background W. US Forecast System
Seasonal Climate Forecast Data Sources
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Approach Bias Correction Scheme
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Approach Bias Example
Sample GSM cell located over Ohio River basin
obs GSM
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VIC initial condition estimation SNOTEL
assimilation
Problem sparse station spin-up period incurs
some systematic errors, but snow state estimation
is critical Solution use SWE anomaly
observations (from the 600 station USDA/NRCS
SNOTEL network and a dozen ASP stations in BC,
Canada) to adjust snow state at the forecast
start date
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VIC model spinup methods SNOTEL assimilation

• Assimilation Method
• weight station OBS influence over VIC cell based
  on distance and elevation difference
• number of stations influencing a given cell
  depends on specified influence distances

• distances fit OBS weighting increased
  throughout season
• OBS anomalies applied to VIC long term means,
  combined with VIC-simulated SWE
• adjustment specific to each VIC snow band

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Results for Winter 2003-04 volume runoff
forecastsComparison with RFC forecast for
Columbia River at the Dalles, OR
UW forecasts made on 25th of each month RFC
forecasts made several times monthly 1st,
mid-month, late (UWs ESP unconditional and
CPC forecasts shown)
UW
RFC
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Results for Winter 2003-04 volume runoff
forecastsComparison with RFC forecast for
Sacramento River near Redding, CA
UW forecasts made on 25th of each month RFC
forecasts made on 1st of month (UWs ESP
unconditional forecasts shown)
RFC
UW
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Results for Winter 2003-04 volume forecastsfor
a sample of PNW locations
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Results for Winter 2003-04 volume forecastsfor
a sample of PNW locations
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Seasonal Hydrologic Forecast Uncertainty

• Importance of uncertainty in ICs vs. climate vary
  with lead time

hence importance of model data errors also
vary with lead time.
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Relative important of initial condition and
climate forecast error in streamflow forecasts
Columbia R. Basin
fcst more impt
ICs more impt
Rio Grande R. Basin
RMSE (perfect IC, uncertain fcst) RMSE (perfect
fcst, uncertain IC)
RE
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Expansion to multiple-model framework

• It should be possible to balance effort given to
• climate vs IC part of forecasts

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Expansion to multiple-model framework
Multiple Hydrologic Models
CCA
NOAA
CAS
CPC Official Outlooks
OCN
NWS HL-RMS
SMLR
CA
Seasonal Forecast Model (SFM)
VIC Hydrology Model
NASA
NSIPP-1 dynamical model
others
ESP
weightings calibrated via retrospective analysis
ENSO
UW
ENSO/PDO
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Winter 2004-5 evolution of a drought and its
prediction
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January 1 SWE forecasts (ensemble averages) using
ESP for JAN-FEB-MAR
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January 1 SWE forecasts (ensemble averages) using
ESP for APR-MAY-JUN
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January 1 SWE forecasts (ensemble averages) using
CPC outlook for JAN-FEB-MAR
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January 1 SWE forecasts (ensemble averages) using
CPC outlook for APR-MAY-JUN
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Next steps

• Improved data assimilation (snow cover extent,
  SNOTEL)
• 2-week forecasts
• Multi-model ensemble (hydrology and climate)
• Forecast domain expansion
• Augmented forecast products (e.g. nowcasts in
  real-time)