Alan HamletDennis P. Lettenmaier

JISAO Climate Impacts Group and the Department of Civil Engineering

University of WashingtonMarch, 2001

CIG Water Resources OutreachLong-Range Strategy

and Assessment of the 2001 Drought

Long-Range StrategySteps to Operational Long-Lead Forecasts for Water Management

•Improve understanding of climate variability

•Develop forecasting techniques

•Develop demonstration applications for specific water

management decision processes

•Retrospectively evaluate the forecasts and demonstrate feasibility

of applications for the historic record

•Outreach to end users and policy makers

•Develop new forecasting infrastructure and appropriate

connections to user community (I.e. implement a PNW Climate

Service)

Climate Forecast

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Schematic for Resampling Forecasting Methods

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cummulative deviationfrom mean

Uncertainties Regarding Decadal Patterns of Variability

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Columbia River Streamflow Forecast at The Dalles for 2001

Highest Simulation (1948-1997)

Lowest Simulation (1948-1997)

Cool PDO/ENSO Neut.Ensemble

http://www.ce.washington.edu/~hamleaf/AWRAWebPaper.html

Long-Term Mean

Post Mortem of 2001 Streamflow Forecast

•2001 ENSO forecast was in error and probably should have called for La Niña instead of ENSO neutral (depends on threshold used).•Uncertainties regarding PDO and assumption in the 2001 forecast of cool phase like 1946-1976 produced some bias towards high flow in the forecasts.•2001 is an extremely unusual water year in the context of the 50 year historic record upon which the forecasts are based, particularly for a La Niña winter. Unusual, but not unheard of --1944 was a very dry water year retrospectively categorized as La Niña, for example. •ENSO telleconnections, which are the primary basis of the forecasts we make, are probably not responsible for the extremely dry year, demonstrating that ENSO forecasts alone are insufficient to predict all kinds of events.

Forecasting Improvements

Improved real time data streams offers the potential for better estimates of initial conditions in real time, and frequent updating of forecasts throughout the winter and spring.

Issues regarding decadal scale patterns of variability may resolve themselves in the next few years simply because of persistence, improving skill of ENSO forecasts with greater confidence.

Improving presentation methods should improve the assessment by potential users of uncertainty in the forecasts.

Effects of Initial Conditions

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Observed Virgin Flow

1992 Estimated Initial Conditions (1954 runup)

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Observed Virgin Flow

1992 Actual Initial Conditions as of Oct 1

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Observed Virgin Flow

1992 Actual Initial Conditions as of Nov 1

1992 Actual Initial Conditions as of Dec 1

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Observed Virgin Flow

1992 Actual Initial Conditions as of Jan 1

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Observed Virgin Flow

1992 Actual Initial Conditions as of Feb 1

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1992 Actual Initial Conditions as of Mar 1

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Observed Virgin Flow

The 2001 Drought

Unusually low winter streamflow has reduced hydro system capacity, and demand has been increasing in recent years.

Financial crisis in the energy industry has resulted in over drafted reservoirs in the Columbia basin.

Normal operations for salmon protection (e.g. spring spill) have apparently been abandoned due to the extremely high costs to the hydro system. The BPA, for example, has estimated that normal spill for salmon could cost on the order of $1 billion.

Hydro system vulnerability may extend into water year 2002 because of low system storage likely to persist into winter of 2001-2002.

Long Range Forecast for Water Year 2002

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Unconditional forecast for The Dalles assuming 1977 initial conditions

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El Niño forecast for The Dalles assuming 1977 initial conditions

ENSO Neutral forecast for The Dalles assuming 1977 initial conditions

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warm ENSO

all years neutral ENSO

Probability of Exceedence April-August Mean Flows

Estimated End of Summer Storage Assuming 1977 Flowsand Initial System Storage 55% of Full Pool

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Normal low flow year

Estimate of this year

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Depletion of Storage at Libby Dam for Winter Energy Production Assuming Initial System Storage of 75% of Full Pool and Average

Winter Energy Loads

Energy Failures

9 Dry Years(most El Niño)

Conclusions Regarding the Drought

•The effects of the 2001 drought will not necessarily abate after 1 year, even though the effects to some uses like irrigation may be greatest this summer.•In the context of energy production, the greatest impacts are likely to be felt in winter 2001-2002, when PNW energy requirements may not be met. The likelihood of such failures will increase if El Niño conditions develop for winter 2001-2002.•The summer of 2002 may bring similar reservoir levels encountered this summer if energy prices remain high, with similar implications for salmon recovery efforts.•The ad hoc reservoir operations for power production this winter have demonstrated a need for better coordination, and have once again emphasized the disparity between the priority of the hydro system and salmon recovery efforts in the Columbia basin.