Seasonal Volume ForecastsSeasonal Volume ForecastsUsing Ensemble Streamflow PredictionUsing Ensemble Streamflow Prediction

for the 2008 Water Yearfor the 2008 Water Year

Ray Fukunaga, Senior HydrologistNorthwest River Forecast Center

Topics for Presentation

ESP and Water Supply Forecast OverviewESP and Water Supply Forecast Overview Recap of WY 2007 Water Supply and ESP Forecasts Recap of WY 2007 Water Supply and ESP Forecasts 2008 Volumetric Streamflow Outlook2008 Volumetric Streamflow Outlook

ESP Water Supply ForecastsESP Water Supply Forecasts ESP with CPC precipitation and temperature shifts appliedESP with CPC precipitation and temperature shifts applied ESP weighting La Nina years onlyESP weighting La Nina years only

NWRFC Forecasting Models

Statistical Water Supply Statistical Water Supply Seasonal Volumetric ForecastsSeasonal Volumetric Forecasts

• Regression techniquesRegression techniques

• 168 forecast locations168 forecast locations

• Coordinated forecasts with NRCS, BOR, COE, and BCHydroCoordinated forecasts with NRCS, BOR, COE, and BCHydro

NWS River Forecast System (NWSRFS)NWS River Forecast System (NWSRFS) Short, Medium, and Longterm capabilities Short, Medium, and Longterm capabilities

• Generates output in deterministic Generates output in deterministic ANDAND probabilistic (ESP) formats probabilistic (ESP) formats

• Variable Outputs for ESPVariable Outputs for ESP

Statistical Water SuppyStatistical Water Suppy

Combined Index:

Observed Precip Observed Snow Observed Runoff

Future Precip

Snow ModelSnow Model

Soil Moisture/RunoffSoil Moisture/Runoff

Consumptive UseConsumptive Use

River Routing River Routing

Reservoir RegulationReservoir Regulation

Flow and Stage Flow and Stage ForecastsForecasts

NWS River Forecast System NWS River Forecast System Model Components (simplified)Model Components (simplified)

Rain Plus Snow Melt

NWS River Forecast System

Time

Fl ow

Day 10

Current timeObserved Forecast

Exceedance probability plotof flow volumes = area under each trace (Jan-Jul period)

50% Value (most expected)is comparable to WS forecasts

Example showing 42 streamflow traces for The Columbia River at The Dalles, OR

Runtime conditions: 9/13/2004Analysis period: 1/1/2005-8/1/2005

Traces represent ensemble of possible river flows (Jan-Jul)

Median Forecast(most expected)

ESP

Water Year 2007 RecapWater Year 2007 Recap

Comparison of ESP and Water Supply Forecast Comparison of ESP and Water Supply Forecast volumes against observed volumevolumes against observed volume LUCI1 Lucky Peak Reservoir Unregulated InflowLUCI1 Lucky Peak Reservoir Unregulated Inflow PLDI1 Palisades Reservoir Unregulated InflowPLDI1 Palisades Reservoir Unregulated Inflow

2007 WS Forecast Recap2007 WS Forecast RecapESP vs WSF Jan-Jul Comparison

LUCI1 ESP vs WSF

400

900

1400

1900

2400

12/17/2006

1/16/2007 2/15/2007 3/17/2007 4/16/2007 5/16/2007 6/15/2007 7/15/2007

Forecast Date

LU

CI1

Ja

n-J

ul V

olu

me

(K

AF

)

90%ESP 50%ESP 10%ESP WSF Mean Min Obs

Monthly Precip (%normal)26 115 43 64 48 57 38

2007 WS Forecast Recap2007 WS Forecast RecapESP vs WSF Jan-Jul Comparison

PLDI1 ESP vs WSF

1400

1900

2400

2900

3400

3900

12/17/2006

1/16/2007 2/15/2007 3/17/2007 4/16/2007 5/16/2007 6/15/2007 7/15/2007

Forecast Date

PL

DI1

Ap

r-J

ul V

olu

me

(K

AF

)

90%ESP 50%ESP 10%ESP WSF Mean Min Obs

Monthly Precip (%normal)53 97 41 87 22 51 75

Spring Outlook - 2008Spring Outlook - 2008

Ensemble Streamflow Prediction (ESP)Ensemble Streamflow Prediction (ESP)

Driven by: Driven by: Antecedent Snow/Soil Moisture Antecedent Snow/Soil Moisture10 day Precip and Temp Forecast10 day Precip and Temp Forecast

Updated weeklyUpdated weekly

Capability of including climate forecasts/signalsCapability of including climate forecasts/signals With CPC temperature and precipitation shiftsWith CPC temperature and precipitation shifts Post-processing using La Nina year weightingPost-processing using La Nina year weighting Not included in current published versionsNot included in current published versions

Volume Forecasts Available at Volume Forecasts Available at www.nwrfc.noaa.govwww.nwrfc.noaa.gov

Min/Mean/Max

441/1778/3200

% of mean

78%

43%

138%

Volume Forecasts Available at Volume Forecasts Available at www.nwrfc.noaa.govwww.nwrfc.noaa.gov

April-July Min/Mean/Max

1089/3331/5621

% of mean

83%% of mean: 42% 117%

ESP Pre-Adjustment Technique

CPC Outlooks are used to shift temperature and precipitation distribution

ESP Year WeightingESP Year Weighting ESP Post Processing: Year WeightingESP Post Processing: Year Weighting

Weighted all >0 average Jul-Sep SOI as 1.0; else 0.0Weighted all >0 average Jul-Sep SOI as 1.0; else 0.0 Reduces sample size of ESP from 45 to 23 yearsReduces sample size of ESP from 45 to 23 years

LUCI1 JAN-JUL vs JUL-SEP SOI

0

500

1000

1500

2000

2500

3000

3500

-2.50 -2.00 -1.50 -1.00 -0.50 0.00 0.50 1.00 1.50 2.00 2.50

July - September Average SOI

LU

CI1

Jan

-Ju

l Vo

lum

e

Mean

WY1983

WY1989WY2007

2007 STANDARD SOI

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

JAN FEB MAR APR MAY JUN JUL AUG SEP

Month

Sta

nd

ard

SO

I

Comparison of ESP 2008 Comparison of ESP 2008 with ESP Climate Adjustedwith ESP Climate Adjusted

COMPARISON OF ESP FORECASTS

70

75

80

85

90

95

10/9ESP% CPC Adj% Jul-SepSOI>0%

% o

f Jan

ua

ry-J

uly

Vo

lum

e N

orm

al

PLDI1 LUCI1

Seasonal Volume ForecastsSeasonal Volume ForecastsUsing Ensemble Streamflow PredictionUsing Ensemble Streamflow Prediction

for the 2008 Water Yearfor the 2008 Water Year

Ray Fukunaga, Senior HydrologistNorthwest River Forecast Center

Ray.Fukunaga@noaa.gov(503) 326-7291