Forecasting Streamflow with the UW Hydrometeorological Forecast System

1. Forecasting Streamflow with the UW Hydrometeorological Forecast System Ed Maurer Department of Atmospheric Sciences, University of Washington Pacific Northwest Weather Workshop March 8, 2003 Photos from: www.metrokc.gov

2. UW Hydromet System and Water Resource Time Scales Weather: floods, drainage, operations Seasonal/Interannual: water supply planning, droughts Climate: climate change, urbanization Ref: A Plan for a New Science Initiativeon the Global Water Cycle, www.usgcrp.gov

3. Accurate representation of spatial and temporal variability in: • Precipitation • Land surface hydrology • is essential for simulating hydrological response at this scale Temporal and Spatial Scales of Hydrologic Variability Ref: A Plan for a New Science Initiativeon the Global Water Cycle, www.usgcrp.gov

4. MM5-DHSVM Streamflow Forecast System UW Real-time MM5 DHSVM Distributed-Hydrology-Soil-Vegetation Model Completely automated In use since WY 1998 For details: Westrick, K.J., P. Storck, and C.F. Mass, Description and Evaluation of a Hydrometeorological Forecast System for Mountainous Watersheds, Weather and Forecasting 17: 250-262, 2002. Streamflow and other forecasts

5. Penn State/NCAR Mesoscale Model MM5 Used throughout the world for both research and operational forecasting 48-hour (and some 72-hour and longer) forecasts run twice daily at the University of Washington High-resolution model (4-km) capable of capturing the complex orography of the region, including lee shading and windward precipitation enhancement FOR MORE INFO... http://www.atmos.washington.edu/mm5rt/

6. DHSVM land surface hydrology model • Physically-based, distributed model • Solves a water balance at each grid cell at each time step • Horizontal scales typically 30m to 150m • Designed for and extensively tested in complex terrain Details on DHSVM at: http://www.hydro.washington.edu/

7. Calibration at 2 sites in Snohomish River Basin Used all available meteorological observations (50sites), 1987-1991 Used flow observations at two USGS gauges: Skykomish R. near Gold Bar Snoqualmie R. at Carnation DHSVM Calibration Snoqualmie R. at Carnation Peaks flows and average water balance are well simulated by DHSVM when forced by observed meteorology

8. UW Hydromet Domain - 2003 26 basins ~60 USGS Gauge Locations 48,896 km2 2,173,155 pixels DHSVM @ 150 m resolution MM5 @ 4 & 12 km http://hydromet.atmos.washington.edu

9. Web Site for Forecast Dissemination • Automatically updated twice daily • Graphic display indicates forecasted flood status • Click through to: • Hydrographs • Snow state (maps and points) • Point weather forecasts

10. Performance of Hydromet System Sauk Snoqualmie Observed MM5-DHSVM NWRFC

11. Of, course, not all forecasts were so bad… Using the Hydromet system for MM5 diagnosis • One exceptionally bad forecast for the Cedar R., events from January 25 to Feb 4, 2003 • Second peak: • Forecast:1200 cfs • Observed: 3700 cfs • Flood stages above bankfull occurred, and were not forecast

12. Average Temperature: Observed: +2.1C Predicted*: -0.1C SWE: Observed: -50 mm Predicted*: +100 mm MM5 biases in P and T combine to produce large underestimation in runoff Temp SWE Representative Meteorological Station – Mt. Gardner Precip Avg. Precipitation from 1/24 - 2/7: Observed: 1.0 mm/h Simulated: 0.7 mm/h Total difference: ~100 mm

13. Opportunity for Improving UW Hydromet Forecasts • 1 – Precipitation/Temperature Bias Correction • Remove systematic biases in P, T, at land surface • 2 – IMPROVE-2 • Take advantage of the IMPROVE-2 experiment to examine the interplay between observation density and bias correction performance • 3 – Initial State Updating • Assimilation of snow and soil moisture information from an observationally constrained data set.

14. Snow State Updating with Observations Use ground observations (SNOTEL sites) to adjust the basin snow state Challenge: 45-50 snow water observations for 48,000 km2 domain – low density places high dependence on interpolation assumptions

15. Probabilistic streamflow forecasts • Take advantage of ensemble MM5 simulations to estimate uncertainty in forecasts Source: Grimit and Eckel, 2003 • Forecasts of slope stability • DHSVM produces more than just streamflow • Soil moistures, slopes in model provide additional forecasting capabilities • Investigate landslide hazard forecasting Probability of failure Image courtesy of L. Bowling Expansion of Forecast Products

16. Summary • UW Hydrometeorological Forecast System provides accurate streamflow and snowpack predictions when forced with accurate meteorology and when properly initialized • Improvements in both initialization and meteorological forecasts are ongoing, by analyzing current flood events and retrospective analysis • The capabilities of the system are being expanded to include both probabilistic forecasts using ensembles, and to include landslide hazard evaluation

17. Acknowledgments

18. Current Streamflow Forecasts • NWRFC provides river flow and stage forecasts at strategic points in Puget Sound region • Use point forecasts of precipitation and temperature • Streamflow produced by a lumped parameter hydrologic model (does not produce spatially distributed water balanceestimates) www.nwrfc.noaa.gov

19. Original Motivation for Developing UW Hydromet System • Integrated modeling over a variety of spatial and temporal scales to examine: • Regionally consistent modeling of weather and land surface hydrology, avoid site-specific calibration • Capture topographically-driven spatial variation in precipitation, temperature, and wind fields • Produce experimental streamflow forecasts to investigate skill in a coupled model setting • Use hydrometeorological forecasts as a diagnostic tool for mesoscale atmospheric model