Andy Wood, Ted Bohn, George Thomas, Ali Akanda, Dennis P. Lettenmaier

University of Washington west-wide experimental hydrologic forecast system

OBJECTIVE The forecasting system was created to evaluate the use of distributed

macroscale hydrologic models for hydrologic forecasting, and provide a testbed for assessing the use of climate predictions and data assimilation in a streamflow forecasting context.

OVERVIEW Forecasts are made once monthly, using simulated initial conditions

based on real-time observations of temperature and precipitation.

Experimental hydrologic forecasts are also made using the climate forecast ensembles derived from the NCEP Climate Prediction Center Seasonal Climate Outlooks.

Benchmark hydrologic forecasts are also constructed via the well-known Extended Streamflow Prediction (ESP) method of the U.S. National Weather Service. The ESP forecasts are also categorized to provide ENSO and PDO-conditioned ensembles, which past work has shown can improve seasonal forecast accuracy.

Major Products of Westwide Forecasting System

References / Acknowledgements

Wood, A.W., E.P. Maurer, A. Kumar and D.P. Lettenmaier, 2002. Long Range Experimental Hydrologic Forecasting for the Eastern U.S., JGR, 107(D20).Liang, X., D. P. Lettenmaier, E. F. Wood and S. J. Burges, 1994. A Simple hydrologically Based Model of Land Surface Water and Energy Fluxes for GSMs, JGR., 99(D7). Wood, A.W. and D.P. Lettenmaier, 2006, A testbed for new seasonal hydrologic forecasting approaches in the western U.S., BAMS (accepted).The authors gratefully acknowledge the support of NOAA/OGP (now the Climate Program Office) CDEP and CPPA programs.

Hydrologic Model (Liang et al., 1994)Hydrologic Forecasting Simulations

Forecast Productsstreamflow soil moisture

runoffsnowpack

derived products

model spin-upforecast ensemble(s)

climate forecast

information

climatology ensemble

1-2 years back start of month 0 end of mon 6-12

NCDC met. station obs. up to

2-4 months from

current

LDAS/other real-time

met. forcings for remaining

spin-up

data sources

snow state information

NRCS SNOTEL / Env. Canada ASP observed SWE anomalies are merged with simulated anomalies to adjust the forecasts’ initial hydrologic state, e.g.:

Forecasts from Climate Model Output

Current Activities

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 over the US westward of the Mississippi River adopting selected experimental reservoir system forecasts as routine products comparing nowcasts with retrospective simulations now in progress extending back to 1915 Expanding the set of streamflow forecast points to the Great Basin, Missouri, and upper Rio Grande Rivers

Other Changes / Ongoing Work

Univ. of Washington

Climate ForecastsESP and ESP/ENSO forecasts• VIC model resolution (1/8 degree)• use ensemble of historical 12 month daily

sequences taken from 1960-99• use subsets based on ENSO category

NCEP CPC Official Outlooks

Snow Assimilation

Components of Overall Real-time Forecasting Approach

example obs SWE anomalies

corresponding SWE adjustment

Forecast Web Page

http://www.hydro.washington.edu/forecast/westwide/

Prior evolution of water balance for drainage area of each forecast location

Spatial Forecasts for P, T, SWE, Soil Moisture, Runoff

Current conditions nowcasts for soil moisture / SWE

• derived from Probability of Exceedence seasonal precipitation and temperature forecasts for US climate divisions

• ensembles of precipitation and temperature generated by non-parameteric resampling approach called the Schaake Shuffle

• from NCEP CFS (in re-development)

Westwide overview map of current water supply period volume forecast

This map clicks through to forecast hydrographs at right, and water balance plots above

Collaboration with Operational and Research Groups

Daily Updating Land Surface Nowcast• Now operational for current domain + Missouri R. basin• Next basins: Mexico, Arkansas-Red, Gulf

We are evaluating the benefits of using three separate models to generate forecasts that can be combined via Bayesian model averaging techniques.

Models: • VIC• SAC – Sacramento /

SNOW17 model (NWS)• NOAH – NCEP, OSU,

Army, NWS Hydrology LabTest Case: Salmon R., ID

Retrospective ComparisonsIndividual Models

Bayesian Model Average

Multiple Land Surface Model Ensembles

Monthly Avg FlowMonthly Avg Flow Monthly RMSEMonthly RMSE

Monthly Avg FlowMonthly Avg Flow Monthly RMSEMonthly RMSE

U. Arizona / USBR

forecast study, Lower Colorado

basin

NWS Hydrologic Ensemble Prediction

Experiment(HEPEX)

3TIER Environmental

Forecast Group

NRCS National Water and Climate Center

Forecast Group

NOAA Climate

Prediction Center’s US

Drought Outlook

Miscellaneous:Seattle City

Light,energy traders,

hydropower utilities,

NOAA regional climate offices

UW Puget Sound region flow forecasts

UW Climate Impacts Group

(CIG)Annual Water

Outlook meetings

NOAA National Centers for

Environmental Prediction

(NCEP) testbed activities

Columbia River Inter-tribal Fish

Commission

Klamath R. Basin

Bureau of Reclamation

UCI / California Dept of Water

Resources

WA State Dept of Ecology &

Yakima R. Basin Bureau

of Reclamation

newUS Drought Monitor

Princeton University Hydrologic Forecast System

UW HydrologicForecast and

NowcastSystems