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A West-wide Seasonal to Interannual Hydrologic Forecast System Andy Wood, Alan Hamlet, Seethu Babu, Marketa McGuire and Dennis P. Lettenmaier 1 Components of Overall Real-time Forecasting Approach OVERVIEW We have implemented the Variable Infiltration Capacity (VIC) macroscale hydrology model over the western U.S. at 1/8 degree spatial resolution for experimental ensemble hydrologic prediction at lead times of six months to 1 year. 2 3 Climate Forecasts Hydrologic Forecasting Simulations start of month 0 1-2 years back Forecasts are made once monthly, using simulated initial conditions based on real-time observations of temperature and precipitation. • T62 (~1.9 degree) resolution • 6 month forecast duration • 20-member ensembles, monthly P, T climatology ensemble NSIPP-1 Tier 1 forecasts • 2 x 2.5 degree (lat x lon) resolution • 7 month forecast duration • 9-member forecast ensembles, monthly P, T data sources NCDC met. station obs. up to 2-4 months from current Experimental hydrologic forecasts are also made, using climate forecast ensembles taken from the NCEP Global Spectral Model (GSM) and the NASA NSIPP-1 model. These will also eventually include the NCEP official seasonal outlooks. LDAS/other real-time met. forcings for remaining spin-up Forecast Products streamflow soil moisture runoff snowpack derived products climate forecast information snow state information ESP forecasts • VIC model resolution (1/8 degree) • historical 12 month daily sequences from 1960-99 Statistical Approach • Bias-correction of climate model ensembles of monthly PCP, TEMP, at climate model scale • Spatial disaggregation to 1/8 degree hydrologic model scale • Temporal disaggregation from monthly to daily time step • detailed in Wood et al. (2002) Major Improvements for Current Forecasting System (starting Sept. ‘03) 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. Primary Upgrades to the forecasting system included: 1) the development of a simple method for assimilating snow water equivalent 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 in lieu of the Land Data Assimilation System (LDAS) real-time forcings. Hydrologic Model (Liang et al., 1994) NCEP Official Outlooks (pending) Review of Pilot Implementation: Columbia River Basin in Winter 2003 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. Downscaling of Climate Model Forecasts NCEP GSM forecasts end of mon 6-12 forecast ensemble(s) model spin-up Benchmark climate forecasts are constructed via the well-known Extended Streamflow Prediction (ESP) method of the U.S. National Weather Service. The ESP forecasts are further composited to provide ENSO and PDO-conditioned ensembles, which past work has shown can considerably reduce seasonal forecast error. 4 Univ. of Washington 5 New Web Page Expanded hydrologic nowcasting / forecasting domain http://www.hydro.washington.edu/Lettenmaier/Projects/fcst/index.htm (ultimately to include US west of Mississippi R., and update weekly, rather than monthly; all at 1/8 degree lat/lon) example obs SWE anomalies corresponding SWE adjustment 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. 2) spin-up met. data improvements method not illustrated Columbia River Sacramento River Selected Results SYNOPSIS: early winter snowpack deficits recovered somewhat, but ultimately led to moderate streamflow deficits in spring and summer. Trinit y Shasta Whiskeytow n Trinity River Initial hydrologic condition estimates Clear Creek Snow Water Equivalent Oroville Sacramento River (SWP) Dam Power Plant River Feather River Dec 28, 2002 American River Jan 15, 2003 Apr 1, 2003 Feb 1, 2003 Folsom Transfer Delta Colorado River Increasing streamflow forecast locations San Joaquin River Delta California Upper Rio Grande R. Basin Snake R. Basin Streamflow hydrograph forecasts (example from February 1) Mokelumne River Delta Outflow Colorado R. Basin Pardee & Camanche Calaveras River Feb 1 New Hogan San Joaquin River San Luis observed observed Stanislaus River New Melones Tuolumne & Merced Rivers Dam Power Plant New Don Pedro & McClure Reservoir system forecast experiments historical mean fcst. ens. mean min percent of normal 90 percent of normal max Simulated System Storage (acre-ft) Simulated System Storage (acre-ft) 6-Month Ensemble Forecasts of System Storage for the Columbia River Basin Using VIC Streamflow Forecasts and the ColSim Reservoir Model Initialized by Observed Reservoir Elevations (~ Feb 1, 2001) adding Dec 03 Streamflow volume forecast comparison with NWS / NRCS computer failure halted UW forecasts official forecasts Apr-Sep Streamflow Forecasts Columbia River at the Dalles, OR 90 percent of normal Transfer Eastman, Hensley, & Millerton 80 70 60 ESP Best Estimate NCEP GSM NRCS NSIPP 50 1-Jan 1-Feb 90 Apr-Sep Streamflow Forecasts Libby Reservoir Inflow 1-Mar forecast date 1-Apr 1-May percent of normal River/Canal 80 70 60 50 1-Jan ESP NRCS Best Estimate NSIPP NCEP GSM 1-Feb 1-Mar forecast date 1-Apr 1-May Apr-Sep Streamflow Forecasts Snake River "near mouth" 80 70 60 ESP Best Estimate NCEP GSM NRCS NSIPP 50 1-Jan 1-Feb 100 Apr-Sep Streamflow Forecasts Dworshak Reservoir Inflow 1-Mar forecast date 1-Apr 1-May adding Dec 03 adding Jan 04 implemented Other Changes / Ongoing Work improving late spin-up forcing procedure through addition of more index stations (currently ~100, with change to 350 in next month) 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 expanding forecast products to include spatial fields (snow water equivalent, soil moisture, runoff) adopting selected experimental reservoir system forecasts as routine products developing a downscaling approach for official forecasts from NCEP and other centers pursuing linkages to NRCS and NWS streamflow forecasting operations groups comparing nowcasts with retrospective simulations now in progress extending back to 1915. 90 References / Acknowledgements 80 ESP NRCS Best Estimate NSIPP NCEP GSM 70 60 50 1-Jan 1-Feb 1-Mar forecast date 1-Apr 1-May Wood, 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). 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 GSMs, J. Geophys. Res., 99(D7). The authors acknowledge the support of NOAA/OGP, the IRI/ARCS Regional Applications Project, and the NASA Seasonal-to-Interannual Prediction Project (NSIPP).