Part II: Experimental seasonal hydrologic forecasting for the Western U.S. Andrew Wood, Alan Hamlet, Dennis Lettenmaier University of Washington JISAO/SMA Climate Impacts Group Columbia River Inter-Tribal Fish Commission Regional Flood Control Workshop February 12, 2004 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.

Outline 1. Overview – Goals – Background 2. Recent and Current Results 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.

Project Domain/Website 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.

UW Experimental West-wide hydrologic prediction system climate model output (NCEP, NSIPP) Real-time Ensemble Forecasts CPC official forecasts (in progress) ESP as baseline fcst Downscaling VIC hydrologic simulations Ensemble Hindcasts (for bias-correction and preliminary skill assessment) UW (Dennis Lettenmaier, Andy Wood and Alan Hamlet) has been exploring an approach for downscaling climate model ensemble forecast output for use in driving real-time hydrologic and streamflow forecast simulations (with the VIC hydrologic model). Currently they’re working with the NCEP GSM, but plan to add other model’s outputs now that they are available (thanks in part to IRI). Down the road, they also plan to use the official tercile format forecasts of some of the forecasting centers a basis for a parallel ensemble set. As a baseline for comparison with the climate model ensembles, they have been using ESP, extended streamflow prediction, in which current hydrologic states are combined with an ensemble of historically observed met. traces in simulating hydrologic forecast ensembles. They use both forecast and hindcast datasets. The hindcasts are useful for bias- correcting the forecast output before downscaling, and also can be run separately as a retrospective forecast assessment. The current UW effort, which focused previously on the Columbia River Basin, is being expanded to the western US domain shown at upper right, and an effort is being made to forge connections with user groups so that forecast products can be tailored to their needs. West-wide forecast products streamflow soil moisture, snowpack tailored to application sectors fire, power, recreation * ESP extended streamflow prediction (unconditional climate forecasts run from current hydrologic state)

Overview: Hydrologic Simulations 1-2 years back start of month 0 end of mon 6-12 forecast ensemble(s) model spin-up initial conditions climatology ensemble NCDC met. station obs. up to 2-4 months from current 2000-3000 stations in west LDAS/other real-time met. forcings for remaining spin-up ~300-400 stations in west climate forecast information data sources Forecast Products streamflow soil moisture runoff snowpack derived products e.g., reservoir system forecasts 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. snow state information (SNOTEL)

Background 1998-9 Ohio R. basin w/ COE: First tried climate model-based seasonal forecasts on experimental (retrospective) basis 2000 Eastern US: First attempted real-time seasonal forecasts during drought condition in southeastern states -- results published in: Wood et al. (2001), JGR 2001 Columbia R. basin: Implemented approach during the PNW drought, again using climate model based approach 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.

Background: CRB 2001 forecasts Initial conditions in spring of 2001 showed large deficits in soil moisture and snowpack.

Background: CRB 2001 forecasts Streamflow forecasts reflected the extreme initial conditions, although did not do as well as NRCS statistical forecasts Note: forecasts were from climate model – but…

Background 1998-9 Ohio R. basin w/ COE: First tried climate model-based seasonal forecasts on experimental (retrospective) basis 2000 Eastern US: First attempted real-time seasonal forecasts during drought condition in southeastern states -- results published in: Wood et al. (2001), JGR 2001 Columbia R. basin: Implemented approach during the PNW drought, again using climate model based approach 2002 Western US: Retrospective analysis of forecasts over larger domain (for one climate model and for ESP) 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.

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

Background 1998-9 Ohio R. basin w/ COE: First tried climate model-based seasonal forecasts on experimental (retrospective) basis 2000 Eastern US: First attempted real-time seasonal forecasts during drought condition in southeastern states -- results published in: Wood et al. (2001), JGR 2001 Columbia R. basin: Implemented approach during the PNW drought, again using climate model based approach 2002 Western US: Retrospective analysis of forecasts over larger domain (for one climate model and for ESP) 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. Columbia R. basin: New funding for “pseudo-operational” implementation for western US; began with pilot project in CRB (Funding from: NASA NSIPP; IRI/ARCS; NOAA GCIP/GAPP)

CRB 2003 forecasts: New spin-up approach 1. interpolate daily anomalies from index stations over domain 2. apply the result to daily averages taken from 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.

CRB 2003 forecasts: Initial snow state assimilation Problem: index station method incurs some systematic errors, but snow 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.

CRB 2003 forecasts: Initial Conditions Dec 28, 2002 Jan 15, 2003 Last winter, alarmingly low December snowpacks mostly recovered by April, although some locations are still well off their long term averages 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.

CRB 2003 forecasts Feb 1 Jan 1 Mar 1 Apr 1

CRB 2003 forecasts: UW/NRCS comparison UW flow volume forecasts 2003 were comparable to the official streamflow forecasts of the National Resources Conservation Service (NRCS) streamflow forecast group (one location shown). computer disk failure halted UW forecasts *UW: ensemble average flow

CRB 2003 forecasts: UW/NRCS comparison 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. *UW: ensemble average flow

Current Forecasting System 1998-9 Ohio R. basin w/ COE: First tried climate model-based seasonal forecasts on experimental (retrospective) basis 2000 Eastern US: First attempted real-time seasonal forecasts during drought condition in southeastern states -- results published in: Wood et al. (2001), JGR 2001 Columbia R. basin: Implemented approach during the PNW drought, again using climate model based approach 2002 Western US: Retrospective analysis of forecasts over larger domain (for one climate model and for ESP) 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. Columbia R. basin: New funding for “pseudo-operational” implementation for western US; began with pilot project in CRB (Funding from: NASA NSIPP; IRI/ARCS; NOAA GCIP/GAPP) 2004 Western US: expanded to western U.S domain for real-time forecasts; working to improve and evaluate methods each forecast cycle

Current 03-04 forecasts: Initial conditions September/October 2003: Soil Moisture

Current 03-04 forecasts: Initial conditions November 25: Snow Water Equivalent (SWE) and Soil Moisture

Current 03-04 forecasts: Initial conditions December 25: Snow Water Equivalent (SWE) and Soil Moisture

Current 03-04 forecasts: Initial conditions January 25: Snow Water Equivalent (SWE) and Soil Moisture

Current 03-04 forecasts: Streamflow Forecasts Expanded from one forecasting location (Dalles) to many

Current 03-04 forecasts: Streamflow Forecasts Current Runoff Volume Forecasts for 2 locations

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