march 21, 2011
DESCRIPTION
Current CBRFC Water Supply Forecast Methodology. March 21, 2011. Kevin Werner NWS Colorado Basin River Forecast Center. Colorado Basin River Forecast Center. One of 13 River Forecast Centers Established in the 1940s for water supply forecasting Three primary missions: - PowerPoint PPT PresentationTRANSCRIPT
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March 21, 2011
Kevin WernerNWS Colorado Basin River Forecast Center
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Current CBRFC Water Supply Forecast Methodology
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Colorado Basin River Forecast Center
One of 13 River Forecast CentersEstablished in the 1940s for water supply forecastingThree primary missions:1. Seasonal Water supply forecasts for water management2. Daily forecasts for flood, recreation, water management3. Flash flood warning support
www.cbrfc.noaa.gov
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Water Supply Forecasts
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Generated seasonally• Typically January through
June• Updated monthly or as
needed
Forecast runoff volume (usually April – July)
Probabilistic
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Web Reference: www.cbrfc.noaa.gov/gmap/gmapm.php?wcon=checked
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Water Supply Forecast Methods
Statistical Forecasting Statistical Regression Equations Primary NOAA/RFC forecast method from 1940’s to mid 1990’s. Primary NRCS/NWCC forecast method Historical Relationships between flow, snow, & precipitation (1971-2000+) Tied to a fixed runoff period (inflexible)
Ensemble Simulation Model Forecasting A component of a continuous conceptual model (NWSRFS) Continuous real time inputs (temperature, precipitation, forecasts) Accounts for soil moisture states (SAC-SMA) - drives runoff efficiency Builds and melts snowpack (Snow-17) – output feeds SAC-SMA Flexible run date, forecast period, forecast parameters. Evolving toward ESP as primary forecast tool at NOAA/RFCs
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Equations built on relationships between the inputs and the output
Statistical Water Supply (SWS)
?
Output Variable: April-July streamflow volume
at Provo-Woodland
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Equations built on relationships between the inputs and the output
Statistical Water Supply (SWS)
Input Variable: Trial Lake Snow
Source: NRCS
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Water Supply Forecast Methods
Statistical Forecasting Statistical Regression Equations Primary NOAA/RFC forecast method from 1940’s to mid 1990’s. Primary NRCS/NWCC forecast method Historical Relationships between flow, snow, & precipitation (1971-2000+) Tied to a fixed runoff period (inflexible)
Ensemble Simulation Model Forecasting A component of a continuous conceptual model (NWSRFS) Continuous real time inputs (temperature, precipitation, forecasts) Accounts for soil moisture states (SAC-SMA) - drives runoff efficiency Builds and melts snowpack (Snow-17) – output feeds SAC-SMA Flexible run date, forecast period, forecast parameters. Evolving toward ESP as primary forecast tool at NOAA/RFCs
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Forecastprecip / temp
General RFC ModelW
eath
er a
nd C
limat
e Fo
reca
sts
RiverForecastSystem
parameters
Observed Data
Analysis &Quality Control
Calibration
modelguidance
Hydrologic Model Analysis
hydrologicexpertise &judgment
OutputsGraphics
River Forecasts
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RFC Models
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Snow Model: SNOW-17 Temperature Index Snow model
RFC forecast uses a snow model and a rainfall-runoff model:SNOW-17: Temperature index model for simulating snowpack accumulation and meltSacramento Soil Moisture Accounting Model: Conceptual hydrologic model used to generate runoff
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Calibration
• Process to assign parameter values to the runoff and snow modules within the model. Unique set for each basin (and sub-basin)
• Quality of calibration can vary greatly from basin to basin depending on data availability, period or record, quality of data, hydrology of the basin, etc.
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San Juan Basin
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San Juan-Pagosa Springs(PSPC2)
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Upper (11000-12644)
Middle (8500-11000)
Lower (7198-8500)
San Juan-Pagosa Springs(PSPC2)
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Weather and Climate Forecasts
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RFC forecast system incorporates both weather and climate forecasts:Weather forecasts integrated into daily operations with forecaster control over point and basin average values
Water supply forecasts typically only use QPF during late season or in lower basinWhen QPF is used, it is used in a deterministic manner
Climate forecasts integrated into seasonal water supply forecasts through probability shifts of forcing ensembleClimate forecasts are typically only considered in lower basin and only in ENSO years
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Forecastprecip / temp
Wea
ther
and
Clim
ate
Fore
cast
s
RiverForecastSystem
parameters
Observed Data
Analysis &Quality Control
Calibration
modelguidance
Hydrologic Model Analysis
hydrologicexpertise &judgment
OutputsGraphics
River Forecasts
Decisions
Rules, values, other factors, politics
Forecast Process
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CBRFC Research Needs
1. Improve precipitation analysis
2. Improve use of weather and climate forecasts
3. Develop reliable ensemble forecast system 4. Improve physical
process understanding and modeling
5. Decision Support: Work with stakeholders to use forecasts
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Water Supply Forecast Overview
SWS (Statistical Prediction)
ESP (Hydrologic Model Prediction)(River
Forecast Centers)
VIPER (Statistical Prediction)
(Water and Climate Center)
Forecast Coordination
Official Coordinated
Forecast
Water Managers and Users
Other Inputs....
Decisions
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Statistical 50% exceedance Forecast:222 kac-ft
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Ensemble 50% exceedance Forecast:230 kac-ft
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ESP applications
CBRFC currently provides “raw” ensemble time series forecasts to several groups:
• Denver Water• Pacificorps (Bear River)• USBR (Gunnison, Utah,
and MTOM)Forecasts updated daily in
winter/springAvailable via CBRFC
webpage23
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Denver Water:• Long history of using ensemble forecasts
for risk management• Download CBRFC ensemble forecasts into
reservoir operations spreadsheet (right)• Optimize reservoir operations by
minimizing negative impacts
LAKE POWELLFORECAST PROBABILITY DISTRIBUTION
OBSERVED INFLOW VOLUMEWATER YEAR 2010
6789
1011121314
AUG-71%
SEP-65%
OCT-55%
NOV-50%
DEC-36%
JAN-21%
FEB-25%
MAR-19%
CHANCE OF EQUALIZATION
MA
F
6.007.008.009.0010.0011.0012.0013.0014.00
required volume
30% exc volume
70% exc volume
50% exc volume
Southern CA MWD:• Requested forecast for probability of
equalization releases from Lake Powell
• USBR determines inflow volume required to trigger equalization from 24 month study
• CBRFC uses regulated ESP forecast to determine probability of reaching the required volume
Applications of Probabilistic Flow Forecasts
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Forecast Coordination
Forecasts are coordinated with NRCS on a monthly basis. Forecasters at each agency compare forecasts, analyze differences, and come up with a official, coordinated forecast.
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NRCS Preferred Forecast:235 kac-ft
NOAA Preferred Forecast:225 kac-ft
Coordinated Forecast:230 kac-ft
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Water Supply Forecast Overview
SWS (Statistical Prediction): 222 KAFESP (Hydrologic Model Prediction) : 230 KAF(River
Forecast Centers)
VIPER (Statistical Prediction) : 236 KAF(Water and
Climate Center)
Forecast CoordinationNOAA: 225 KAFNRCS: 236 KAF
Official Coordinated
Forecast:230 KAF
Water Managers and Users
Other Inputs....
Decisions
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Forecast Verification
www.cbrfc.noaa.gov -> Water Supply -> Verification
Beginning in 2008, CBRFC began verifying all water supply forecasts both for current year and systematically over previous years
Current forecast system has skill
SWS and ESP have somewhat different error characteristics
Skill is typically near zero in Jan/Feb and increases substantially into spring
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Discussion
• Unmet stakeholder requirements:• Assessment and incorporation of weather and climate forecasts
into water supply forecasts• Forecast horizon out to two years• Objective (and therefore repeatable) forecast system
• CBRFC is committed to working with partners (you all) to meet these and other requirements
• Need to move forward in a responsible way that builds on or bridges from current forecast system
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