Seasonal outlooks for hydrology and water resources: streamflow forecasts for the Columbia River basin Andrew Wood Alan Hamlet Marketa McGuire Dennis Lettenmaier University of Washington The Climate Impacts Group Annual Fall Forecast Meeting Kelso, WA October 14, 2003 important points: Arun Kumar works for the NCEP Environmental Modeling Center, Climate Modeling Branch and runs the global spectral model to produce forecasts. this study period and region are important because there is an evolving drought that we would like to use as a test situation for the method’s skill. this approach was previously applied to the East Coast during Summer 2000, when there was an evolving drought in that region – a paper evaluating the project is currently submitted to JGR-Atmospheres.

S/I Hydrologic Forecasting Project www.hydro.washington.edu/Lettenmaier/Projects/fcst/index.htm

Goals of UW Forecasting Project Produce real-time ensemble forecasts: based on experimental climate model forecast products based on established methods (such as ESP) of streamflow, for selected large river basins (primarily in the West) of snowpack / soil moisture anomalies Assess experimental product skill relative to established forecast products Evaluate relative hydrologic prediction skill due to ICs - initial land surface conditions (soil moisture, snow) and due to climate forecast skill.

Outline Project Overview hydrologic model-based approach spin-up: initial condition estimate suite of climate forecasts Last year’s forecast results (brief review) Current Columbia River basin forecasts initial conditions hydrologic forecasts reservoir forecasts important point(s): the approach attempts to make use of forecast skill from 2 sources: better understanding of synoptic scale teleconnections and the effects of persistence in SSTs on regional climate, as reproduced in coupled ocean-atmosphere models; the macroscale hydrologic model yields an improved ability to model the persistence in hydrologic states at the regional scale (more compatible with climate model scales than prior hydrologic modeling). Climate forecasts with monthly and seasonal horizons are now operationally available, and if they can be translated to streamflow, then they may be useful for water management.

Overview: VIC Hydrologic Model important point(s): VIC is a water & energy balance with some subgrid scale approximations for vegetation, elevation and soil dynamics, and has a crude routing that works as a post processor. VIC has been applied to a number of continental scale river basins around the world and is well documented in the literature.

Overview: Hydrologic Modeling Simulations for 1950-current climatology, presently extending back to 1915-current Five major basins ~100 streamflow locations, currently

Model-based Forecasting Approach General streamflow, soil moisture, snowpack, runoff local scale weather inputs forecast ensemble meteorological sequences downscaling process * hydrologic simulation * for climate model forecasts VIC Hydrology Model 1/8 degree resolution daily P, Tmin, Tmax NASA NSIPP-I Forecasts 2-2.5 degree resolution monthly total P, avg T NCEP GSM Forecasts 1.9 degree resolution Experimental forecast applications important point(s): the overall forecasting approach involves using forecast model (the global spectral model) T & P output at a coarse timestep & scale as hydrologic model input at a finer timestep and scale. to make a hydrologic forecast, you need a transformation of the forecasts that first overcomes climate model bias and the scale differences, then simulates the water balance. also, GSM is really run at very fine timestep (~5-15 minutes) but only the monthly anomalies are archived for our use. most of the signal is at the monthly scale, however, so this is acceptable.

Overview: VIC Simulations Forecast Products streamflow soil moisture runoff snowpack derived products VIC model spin-up forecast 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 important point(s): after bias correcting and downscaling the climate model forecasts, the procedure for producing hydrologic forecasts is as follows: we spin up the hydrologic model to the start of the forecast using observed met. data (from 2 sources: NCDC cooperator stations through 3-4 months before the start of the forecasts, then LDAS 1/8 degree gridded forcings thereafter). The GSM forecasts comprise 2 sets of ensembles, one for climatology and one for the forecast. The climatology ensemble yields a distribution of the conditions we’ve seen over the period 1979-1999, while the forecast ensemble yields the distribution of the conditions we might see for the next 6 months. Although the climatology ensemble is nominally unbiased against a simulated climatology based on observed met. data (rather than bias-corrected, downscaled GSM met. forcings), we compare the forecast and GSM climatology so that any unforeseen biases (resulting, perhaps, from the downscaling method) occur in both climatology and forecast. Eventually this cautionary step may be eliminated, and we’ll compare directly to the simulated observed climatology. at the end of the spin-up period and one month before month 1 (out of 6) of the forecasts, we save the hydrologic model state. The state is then used for initializing the forecast runs. Through the first month, the model runs on observed data to the last date possible, then switches to the forecast data. Usually, we process the observed forcings up through the 15th to 25th of this initialization month, then the forecast forcing data carries the run forward for the remaining days in the month, and throughout the following 6 month forecast period. Note, the state files used for the climatology runs correspond to the spin-up associated with the particular year (out of 1979-1999) from which the climatology ensemble member is drawn. the spin-up period captures the antecedent land surface hydrologic conditions for the forecast period: in the Columbia basin, the primary field of interest is snow water equivalent. forecast products are spatial (distributed soil moisture, runoff, snowpack (swe), etc.), and spatial runoff + baseflow is routed to produce streamflow at specific points, the inflow nodes for a management model, perhaps.

Overview: Spin-up approach Problem: For most recent 2-2.5 months, meteorological data availability is poor 1-2 years before start date: dense station network (~1000), forcings consistent with those used in model calibration, etc. (mostly COOP stations) 2-2.5 months prior to start: coarse reporting network (~150 stns, some COOP) density lower in Canada. Solutions: > LDAS 1/8 degree real-time forcings from NOAA/NASA > Index station method: combine coarse network signals with dense station climatology important point(s): the approach attempts to make use of forecast skill from 2 sources: better understanding of synoptic scale teleconnections and the effects of persistence in SSTs on regional climate, as reproduced in coupled ocean-atmosphere models; the macroscale hydrologic model yields an improved ability to model the persistence in hydrologic states at the regional scale (more compatible with climate model scales than prior hydrologic modeling). Climate forecasts with monthly and seasonal horizons are now operationally available, and if they can be translated to streamflow, then they may be useful for water management.

Overview: Spin-up approach, Index Stn Method 1. interpolate monthly percentiles from sparse index stations to 1/8 degree grid 2. find percentiles’ matching amounts in the dense station-derived climatology important point(s): the approach attempts to make use of forecast skill from 2 sources: better understanding of synoptic scale teleconnections and the effects of persistence in SSTs on regional climate, as reproduced in coupled ocean-atmosphere models; the macroscale hydrologic model yields an improved ability to model the persistence in hydrologic states at the regional scale (more compatible with climate model scales than prior hydrologic modeling). Climate forecasts with monthly and seasonal horizons are now operationally available, and if they can be translated to streamflow, then they may be useful for water management.

Overview: Spin-up approach, Index Stn Method Example for monthly precipitation percentiles interpolated to 1/8 degree grid pcp percentile matching 1/8 degree pcp amts Index stn pcp important point(s): the approach attempts to make use of forecast skill from 2 sources: better understanding of synoptic scale teleconnections and the effects of persistence in SSTs on regional climate, as reproduced in coupled ocean-atmosphere models; the macroscale hydrologic model yields an improved ability to model the persistence in hydrologic states at the regional scale (more compatible with climate model scales than prior hydrologic modeling). Climate forecasts with monthly and seasonal horizons are now operationally available, and if they can be translated to streamflow, then they may be useful for water management. lastly, daily seqences from stations applied to monthly grid cell totals, and rescaled to produce estimated monthly amounts.

Overview: Initial snow state assimilation Problem: index station method incurs some bias, but snow/SM state estimation is critical Solution: use SWE observations (from the 600+ station USDA/NRCS SNOTEL network and several ASP stations in BC, Canada, run by Environment Canada) to adjust snow state at the forecast start date important point(s): the approach attempts to make use of forecast skill from 2 sources: better understanding of synoptic scale teleconnections and the effects of persistence in SSTs on regional climate, as reproduced in coupled ocean-atmosphere models; the macroscale hydrologic model yields an improved ability to model the persistence in hydrologic states at the regional scale (more compatible with climate model scales than prior hydrologic modeling). Climate forecasts with monthly and seasonal horizons are now operationally available, and if they can be translated to streamflow, then they may be useful for water management.

Overview: Suite of Forecasts Ensemble Streamflow Prediction (ESP) ESP method with ENSO and ENSO/PDO compositing Climate model-based forecasts CPC official forecasts (still in development) important point(s): GSM forecasts take the form of monthly ensembles of length 6 months we get them early in each month for a start date of the following month. the climatology ensemble enables us to define the climate model bias and correct it climatology ensembles run out 6 months just like the forecasts, but use observed rather than predicted tropical Pacific SSTs also: 210 ensembles for GSM climatology are derived from observed SSTs in each year of the 21 year climatology period (1979-1999) combined with 10 initial atmospheric conditions for each year GSM is at T42 spatial resolution, but moving to T62 soon (resolution improvement of about 1/3)

Overview: 1. ESP method NWS River Forecast Center (RFC) approach: rainfall-runoff modeling (i.e., NWS River Forecast System, Anderson, 1973 offspring of Stanford Watershed Model, Crawford & Linsley, 1966) Ensemble Streamflow Prediction (ESP) used for shorter lead predictions; a variation is used for longer lead predictions The RFC final seasonal forecasts also incorporate NRCS results. ICs Spin-up Forecast obs RMSE recently observed meteorological data ensemble of met. data to generate forecast ESP forecast hydrologic state

Overview: Hydrologic prediction, an aside active Snow water content on April 1 should add my personal pics of - snow sampling snotel sites (and scan in curve method figure) SNOTEL network NRCS SNOTEL Network McLean, D.A., 1948 Western Snow Conf. April to August runoff

Overview: 2. ESP-based composites Columbia River at The Dalles, OR Blue = all years 1900-2002 Green = all enso neutral 1900-2002 (33) Red = enso neutral 1961-2002 (12)

Overview: 3. Climate model-based forecasts Seattle

Overview: Climate model-based forecasts Previously, demonstrated our approach for combining seasonal climate model forecasts with hydrologic simulation to create hydrologic forecasts Climate Model: NCEP Global Spectral Model (GSM) Hydrology Model: VIC (at 1/8 or 1/4 degree resolution) Real-time experimental applications: East Coast (Spring-Summer 2000, November 1997) (paper: Wood et al. (2001), JGR) Columbia R. basin (Spring-Summer 2001) Columbia R. basin (Winter-Spring 2003) important point(s): the approach attempts to make use of forecast skill from 2 sources: better understanding of synoptic scale teleconnections and the effects of persistence in SSTs on regional climate, as reproduced in coupled ocean-atmosphere models; the macroscale hydrologic model yields an improved ability to model the persistence in hydrologic states at the regional scale (more compatible with climate model scales than prior hydrologic modeling). Climate forecasts with monthly and seasonal horizons are now operationally available, and if they can be translated to streamflow, then they may be useful for water management.

Overview: 3. Climate model-based forecasts bias-correcting… then downscaling… CRB domain, June precip

Overview: 3. Climate model-based forecasts …and temporal disaggregation VIC-scale monthly Tavg forecast

Overview: 3. Climate model-based forecasts

Overview: 4. CPC Official Forecasts (seasonal) Note: Consensus forecasts based on a number of methods CANONICAL CORRELATION ANALYSIS COMPOSITE ANALYSIS OPTIMAL CLIMATE NORMALS METHOD CONSTRUCTED ANALOG ON SOIL MOISTURE SCREENING MULTIPLE LINEAR REGRESSION CLIMATE MODEL

Overview: CPC Official Forecasts (seasonal)

Forecast Results: A quick look at last year Updates Dec 28, 2002 Jan 15, 2003 Feb 1 Feb 15 Mar 1 Mar 16 Apr 1 ESP ESP, GSM, NSIPP important point(s): the approach attempts to make use of forecast skill from 2 sources: better understanding of synoptic scale teleconnections and the effects of persistence in SSTs on regional climate, as reproduced in coupled ocean-atmosphere models; the macroscale hydrologic model yields an improved ability to model the persistence in hydrologic states at the regional scale (more compatible with climate model scales than prior hydrologic modeling). Climate forecasts with monthly and seasonal horizons are now operationally available, and if they can be translated to streamflow, then they may be useful for water management.

Last year: Initial Conditions Dec 28, 2002 Jan 15, 2003 This past winter, we had alarmingly low PNW December snowpacks Many areas recovered by April, but not the Cascades Feb 1, 2003 Mar 1, 2003 Apr 1, 2003 important point(s): the approach attempts to make use of forecast skill from 2 sources: better understanding of synoptic scale teleconnections and the effects of persistence in SSTs on regional climate, as reproduced in coupled ocean-atmosphere models; the macroscale hydrologic model yields an improved ability to model the persistence in hydrologic states at the regional scale (more compatible with climate model scales than prior hydrologic modeling). Climate forecasts with monthly and seasonal horizons are now operationally available, and if they can be translated to streamflow, then they may be useful for water management.

Last year: streamflow (ESP/NSIPP/GSM) Dec 1 ESP and climate model forecasts were fairly similar, all reflecting the low moisture initial conditions Apr 1

Last year: UW/NRCS comparison UW pilot results were comparable to the official streamflow forecasts of the National Resources Conservation Service (NRCS) streamflow forecast group. Note: estimate given by Jun 1 NRCS forecast UW pilot forecasts halted

Last year: UW/NRCS comparison ensemble median flow important point(s): the approach attempts to make use of forecast skill from 2 sources: better understanding of synoptic scale teleconnections and the effects of persistence in SSTs on regional climate, as reproduced in coupled ocean-atmosphere models; the macroscale hydrologic model yields an improved ability to model the persistence in hydrologic states at the regional scale (more compatible with climate model scales than prior hydrologic modeling). Climate forecasts with monthly and seasonal horizons are now operationally available, and if they can be translated to streamflow, then they may be useful for water management.

Current Columbia River basin forecasts important point(s): the approach attempts to make use of forecast skill from 2 sources: better understanding of synoptic scale teleconnections and the effects of persistence in SSTs on regional climate, as reproduced in coupled ocean-atmosphere models; the macroscale hydrologic model yields an improved ability to model the persistence in hydrologic states at the regional scale (more compatible with climate model scales than prior hydrologic modeling). Climate forecasts with monthly and seasonal horizons are now operationally available, and if they can be translated to streamflow, then they may be useful for water management.

Current Forecasts: Initial Conditions CPC Percent of Normal Precip September 25, 2003 Jun-Jul-Aug % Sep important point(s): the approach attempts to make use of forecast skill from 2 sources: better understanding of synoptic scale teleconnections and the effects of persistence in SSTs on regional climate, as reproduced in coupled ocean-atmosphere models; the macroscale hydrologic model yields an improved ability to model the persistence in hydrologic states at the regional scale (more compatible with climate model scales than prior hydrologic modeling). Climate forecasts with monthly and seasonal horizons are now operationally available, and if they can be translated to streamflow, then they may be useful for water management.

Current forecasts: streamflow (ESP-based)

Current forecasts: streamflow (ESP-based)

Current forecasts: streamflow (ESP-based)

Current forecasts: streamflow (ESP-based)

Current forecasts: streamflow (ESP-based)

Current forecasts: Reservoir system storage Simulated streamflows Reservoir model inputs Unconditional ESP ENSO-neutral forecast Full Pool ensemble mean

Current forecasts: Snake River locations Upper Snake Storage Forecast

Current forecasts: Reservoir system storage Unconditional ESP System Storage Forecast from SnakeSim includes: Jackson Lake Palisades Island Park Ririe American Falls Lake Walcott Full Pool ensemble mean

Current forecasts: Still to come Products in development: spatial forecasts of SWE, Runoff and SM, e.g. expanding to rest of the West improved spin-up procedure retrospective forecast verification

Conclusions Currently normal to slightly low soil moisture conditions in the runoff producing areas east of Cascades; very low west of Cascades Streamflow forecasts for summer 2004 appear close to normal in most locations Subsequent forecasts are worth waiting for: improved initial condition estimation as snow, SM rebuild methodological improvements www.hydro.washington.edu/Lettenmaier/Projects/fcst/index.htm