1. Update on West Wide Hydrologic Forecasting at the University of Washington
Dennis P. Lettenmaier, Andrew W. Wood, Ted Bohn, George Thomas
Univ. of Washington
Components of Real-time Forecasting Approach
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.
Climate Forecasts
Hydrologic Model (Liang et al., 1994)
Snow Assimilation
Hydrologic Forecasting Simulations
Forecast Products
streamflow
soil moisture
runoff
snowpack
derived products
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
ESP and ESP/ENSO forecasts
NRCS SNOTEL / Env. Canada ASP observed SWE anomalies are merged with simulated anomalies to adjust the forecasts’ initial hydrologic state, e.g.:
VIC model resolution (1/8 degree)
use ensemble of historical 12 month daily sequences taken from
use subsets based on ENSO category
corresponding SWE adjustment
example obs. SWE anomalies
NCEP CPC Official Outlooks
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
Forecasts from Climate Model Output
from NCEP CFS (in re-development)
Major Products of Westwide Forecasting System
Current Activities
Forecast Web Page
Collaboration with Operational and Research Groups
During the last year, forecast system activities have included:
the continued production of monthly forecasts
implementation of automatic calibration approach
an expansion of forecast products
increasing interaction with NOAA groups (EMC and NWS WRSC)
a major effort to re-stage the system on a Linux cluster, including:
fully automated daily updates, rather than semi-automated monthly
development of additional forecast points in new domain areas
Current conditions nowcasts for soil moisture / SWE
Notable interactions with external groups:
Forecast inter-comparison with RFC and NRCS
Interaction with NCEP EMC
Interaction with USBR on lower Colorado R.
Spatial Forecasts for P, T, SWE, Soil Moisture, Runoff
Expansion of Nowcast simulation domain
Prior evolution of water balance for drainage area of each forecast location
Nowcasts of WY 2006 showing response to strong
North American monsoon precipitation
Missouri R. basin added in August
Mexico also added to daily update simulations, but a modified approach is needed to accommodate unreliable forcing
Other Changes / Ongoing Work
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
West-wide overview map of current water supply period volume forecast
References / Acknowledgements
Wood, A.W., E.P. Maurer, A. Kumar and D.P. Lettenmaier, 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, 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 (in press).
The authors gratefully acknowledge the support of NOAA/OGP (now the Climate Program Office) CDEP and CPPA programs.
This map clicks through to forecast hydrographs at right, and water balance plots above