Mid-Range Water Supply Forecasts for Municipal Water Supplies

Matthew Wiley, Richard Palmer, and Michael

Miller

Department of Civil and Environmental Engineering

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Today’s Presentation Need for forecast Describe approach Present forecasts Introduce Website

www.tag.washington.edu

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Goals Evaluate the value of a 6-month

meteorological forecast in making water resources decisions

Use meteorological forecast to create a forecast of streamflows Evaluate the meteorological data Evaluate the hydrologic response

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Seattle Public Utilities

Tacoma Water

Everett Public Utilities

Partner Utilities

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Problem Setting Project Setting – Puget Sound

Region Water supply to 2.6 million Flood Control Navigation Hydropower Environmental

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Water Supply Utility Challenges Provide safe, reliable and inexpensive

drinking water Preserve environmental quality,

demonstrate resource stewardship Maintain/enhance Infrastructure Provide stable and economically viable

rate structure Adapt to evolving water quality

requirements

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Primary Purposes of Forecast Refill decisions in spring Supply evaluation in early summer Decisions related to fish flows

(when is water most needed) Curtailment decisions in late

summer Drawdown decisions in fall

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Value of Forecast Utility has established operating

policies Forecast is valuable if it provides

information that modifies policy and forecast is correct

Accurate forecasts of normal, below, or above normal are desired (can result in policy change)

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Approaches

Historical Streamflows Assume averages are sufficient

Ensemble Streamflow Predictions (ESP) Well-established approach Used by Weather Service Can be conditioned on climate

condition

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ESP Forecast

obs

Recently ObservedMeteorological Data

Ensemble of Meteorological

Data to Generate forecast

ICsSpin-up Forecast

hydrologicstate

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Approaches

National Centers for Environmental Prediction (NCEP) 6-month forecasts Uses Global Climate Model to produce

forecast ensembles Can be compared to ESP

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National Centers for Environmental Prediction (NCEP) climate forecast.

Initial and PredictedSST for next6 months

20 differentInitial statesof the atmosphere

20 unique forecasts of the climate over the next six months

We use the raw model output at this point.

2x2 degree GSMCoupled Ocean-AGCM

OfficialNCEP ClimateForecast

Correlation AnalysisPast ExperienceProbability Mapping

20 Ensemble Forecast

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National Centers for Environmental Prediction (NCEP) climate forecast.

Initial and PredictedSST for6 months

10 differentinitial states that existedof the atmosphere

10 unique hindcasts of the climate for each year over the next six months

We use Hindcasts for bias correction and retrospective analysis

2x2 degree GSM

Coupled Ocean-AGCM

OfficialNCEP ClimateForecast (210 hindcasts)

Used in conjunction with forecasts for bias correction

10 Ensemble Hindcasts

Years

1979

1980

1981

1999

Years

1979

1980

1981

1999

21 year

s

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Forecasts being produced

ESP NCEP http://www.tag.washington.edu/

projects.html

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South Fork Tolt River, August 2004, Unconditioned ESP

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South Fork Tolt River, August 2004, ENSO based ESP

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Tentative Conclusions Streamflow Forecast

In small west slope basins, NCEP is generally more useful than ESP

Monthly forecast Poor in December Better in later months of the forecast

Seasonal Forecast Better in the spring and early summer Poor in late winter

NCEP is in the process of revising its mid-range forecasting procedures

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Future Work continues

Water Temperature Modeling Improve Web Viewing Continue With Forecasts Additional Evaluation of the Quality of

the Forecast Conditional evaluations Evaluate other types of Forecasts IRI, CPC

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Stream Temperature Forecasts

Conditions at USGS 12147600, South Fork Tolt River, above S.F.T. Reservoir

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CF

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012345678910111213141516

deg

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Observed Temperature

Observed Flow

Simulated Temperature

Simulated Flow

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Stream Temperature Forecasts

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Future Work continues

Water Temperature Modeling Improve Web Viewing Continue With Forecasts Further Evaluation of Forecast Quality Consider other climate forecasts: IRI, CPC Additional Water Supply Basins

White River Bull Run Tualatin

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Web Page

http://www.tag.washington.edu Projects

Mid-Range Forecasts