Apr-Sep Runoff Volume ForecastColumbia River at the Dalles, OR

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1-Jan 1-Feb 1-Mar 1-Apr 1-Mayforecast date

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ESP NWS/NRCSObs NSIPPNCEP GSM

2003 Summer streamflow volume forecast comparison with NWS / NRCS official forecasts

Andy Wood, Alan Hamlet, Seethu Babu, Marketa McGuire and Dennis P. Lettenmaier

A seasonal hydrologic forecast system for the western U.S.

OVERVIEW We have implemented the Variable Infiltration Capacity (VIC)

hydrology model over the western U.S. at 1/8 degree spatial resolution for ensemble hydrologic prediction at lead times of 6 months to 1 year.

Real-time hydrologic forecasts are made once monthly using initial conditions simulated with real-time observations of temperature and precipitation, and adjusted via the assimilation of SNOTEL snow water equivalent and, experimentally, MODIS snow-covered area.

Benchmark climate forecasts are constructed via the well-known Extended Streamflow Prediction (ESP) method of the National Weather Service. The ESP forecasts are further composited to provide ENSO and PDO-conditioned ensembles.

Experimental hydrologic forecasts are also made using climate forecast ensembles derived from the NCEP Global Spectral Model (GSM), the NASA NSIPP-1 model, and the CPC official seasonal outlooks. These are used to drive experimental reservoir forecasts in some locations.

Expansion to Current Forecasting System (starting Sept. 2003)

References / AcknowledgementsWood, A.W., E.P. Maurer, A. Kumar and D.P. Lettenmaier, 2002. Long Range Experimental Hydrologic Forecasting for the Eastern U.S., J. Geophys. Res., 107(D20).Wood, A.W., A. Kumar and D.P. Lettenmaier, 2004, A retrospective assessment of NCEP GSM-based ensemble hydrologic forecasting in the western U.S., J. Geophys. Res. (in review)Liang, X., D. P. Lettenmaier, E. F. Wood and S. J. Burges, 2004. A Simple Hydrologically Based Model of Land Surface Water and Energy Fluxes for GCMs, J. Geophys. Res., 99(D7).Clark, M., S. Gangopadhyay, L. Hay, B. Rajagopalan and R. Wilby, 2004. The SCHAAKE Shuffle: A method for reconstructing space-time variability in forecasted precipitation and

temperature fields, J. Hydrometeorology, 5, 243-262.The authors acknowledge the support of NOAA/OGP, the IRI/ARCS Regional Applications Project, and the NASA Seasonal-to-Interannual Prediction Project (NSIPP).

Hydrologic Model (Liang et al., 1994)Hydrologic Forecasting SimulationsClimate Model ForecastsA retrospective hydroclimatology is used for:• Statistical bias-correction of climate model

ensembles of monthly P, T at climate model scale• Spatial disaggregation to 1/8 degree hydrologic

model scale• Temporal disag. from monthly to daily time step• detailed, assessed in Wood et al. (2002, 2004)

Our initial forecast domain was the Pacific Northwest. Real-time bi-monthly updates began at the end of December, 2002, and ran through April 2003.

NCEP GSM forecasts• T62 (~1.9 degree) resolution• 6 month forecast duration• 20-member ensembles, monthly P, T

NSIPP-1 Tier 1 forecasts• 2 x 2.5 degree (lat x lon) resolution• 7 month forecast duration• 9-member ensembles, monthly P, T

Review of Pilot Implementation: Columbia River Basin in Winter 2003

Dam

Power Plant

River/Canal

Transfer

Eastman, Hensley, & Millerton

New Don Pedro & McClure

Delta

New Hogan

Pardee & Camanche

Stanislaus River

Tuolumne & Merced Rivers

Delta Outflow

Mokelumne River

Calaveras River

San

Joaquin

R

iver

New Melones

San Luis

Trinity

Whiskeytown

Shasta

Oroville (SWP)

Folsom

Clear Creek

American River

Feather River

Trinity River

Sac

ram

ento

R

iver

Dam

Power Plant

River

TransferDelta

Colorado River San Joaquin River

Columbia River Sacramento River

UW forecasts halted

Jan 15, 2003Dec 28, 2002 Feb 1, 2003 Apr 1, 2003

Snow Water Equivalent

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1) NRCS SNOTEL / EC ASP observed SWE anomalies are interpolated in distance and elevation to hydrologic grid cell elevation bands, and linearly combined with simulated anomalies, to adjust the hydrologic model state at the start of the forecast.

2) spin-up met. data improvements method / MODIS experiments not illustrated

Streamflow hydrograph forecasts (example from February 1)

Initial hydrologic condition estimates

Reservoir system forecast experiments

re-evaluating the NASA/NOAA NLDAS 1/8 degree forcing product as a potential real-time forcing in Western U.S. automating nowcast / initial condition simulation to occur on weekly basis adopting selected experimental reservoir system forecasts as routine products comparing nowcasts with retrospective simulations now in progress extending back to 1915 (rather than 1960).

Ongoing Work

Univ. of Washington

Climate Forecasts

ESP forecasts• VIC model resolution (1/8 degree)• historical 12-month daily

sequences from 1960-99

CPC Official Outlooks

Downscaling

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Components of Overall Real-time Forecasting Approach

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max

fcst. ens. mean

historical mean

Selected Results

Primary Upgrades to the forecasting system included:1) the implementation of a simple method for assimilating snow water equivalent (SWE) observations at the start of the forecast,

2) a modification of the surface forcing estimation immediately prior to the forecast start using a set of real-time index stations

We began adapting a set of reservoir system models for the western U.S to produce ensemble forecasts of reservoir system storages, operations and releases.

example obs SWE anomalies

corresponding SWE adjustment

6-Month Ensemble Forecasts of System Storage for the Columbia River BasinUsing VIC Streamflow Forecasts and the ColSim Reservoir Model Initialized by Observed

Reservoir Elevations (~ Feb 1, 2001)

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SYNOPSIS: early winter snowpack deficits recovered somewhat, but ultimately led to moderate streamflow deficits in spring and summer.

Forecasts posted on web page

www.hydro.washington.edu/Lettenmaier/Projects/fcst/

Feb 1

observed observed

NCDC met. station obs.

up to 2-4 months from

current

local scale (1/8 degree) weather inputs

soil moisturesnowpack

Hydrologic model spin up

SNOTELUpdate

streamflow, soil moisture, snow water equivalent, runoff

25th Day, Month 01-2 years back

LDAS/ other real-time

met. forcings for spin-up

gap

Hydrologic forecast simulation

Month 6 - 12

I NI TI AL STATE

SNOTEL/ MODIS*Update

ensemble forecastsESP traces (40)CPC-based outlook (13)NCEP GSM ensemble (20)NSIPP-1 ensemble (9)

NCDC met. station obs.

up to 2-4 months from

current

local scale (1/8 degree) weather inputs

soil moisturesnowpack

Hydrologic model spin up

SNOTELUpdate

streamflow, soil moisture, snow water equivalent, runoff

25th Day, Month 01-2 years back

LDAS/ other real-time

met. forcings for spin-up

gap

Hydrologic forecast simulation

Month 6 - 12

I NI TI AL STATE

I NI TI AL STATE

SNOTEL/ MODIS*Update

ensemble forecastsESP traces (40)CPC-based outlook (13)NCEP GSM ensemble (20)NSIPP-1 ensemble (9)

* experimental, not yet in real-time product

• based on 102 Climate Divisions• 13-member ensemble derived from monthly P, T probability distributions

CPC Outlooks• Resampling approach (the Schaake Shuffle of

Clark et al., 2004) creates ensemble traces.• Spatial/temporal disaggregation as above

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Snow Water EquivalentSoil Moisture

Streamflow Forecasts

Apr-Sep Runoff Volume Forecast Snake River "near mouth"

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Apr-Sep Runoff Volume Forecast Libby Reservoir Inflow

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Apr-Sep Runoff Volume ForecastDworshak Reservoir Inflow

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ESPNWS/NRCSObsNSIPPNCEP GSM

Example forecast for 2 (of ~50 active) locations(from March 25 initial conditions)

Verification / Comparison with RFC runoff volume forecasts

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In late March, initial conditions (at left) reflect below average moisture (soil and snow) in the mountains of the central and northern. ID, but early snowmelt in the lower areas of eastern WA and OR, and northern CA. These led to below average forecasts of summer streamflow for the Columbia River (location 1), which drains the PNW, and above average flow forecasts for the Sacramento River (location 2), which drains areas of NE California and south central OR.

The UW Columbia R. ESP forecast (right) showed in fall 2003 that, due to low soil moisture and below average early snowpack in southern British Columbia, runoff would likely be below average. The NWS forecasts predicted near normal summer runoff until late Feb. and Mar., when dry and warm conditions abruptly reduced western US snowpacks, after which they converged toward the UW forecasts at about 80 percent of long-term average runoff.

In N. California, similarly, low fall soil moistures indicated low summer runoff, but then snowpacks grew deeper than normal until their early melt in March. The UW ESP forecasts reflect these conditions.

Spatial forecasts related to historical conditions(as anomalies and percentiles w.r.t. 1960-99)

Example: NCEP Global Spectral Model (GSM) forecasts

(leads 1-3 months shown, for May 25 initial conditions)