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:

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

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

MM5-DHSVM Streamflow Forecast System 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: , Streamflow and other forecasts DHSVM UW Real-time MM5 Distributed-Hydrology-Soil-Vegetation Model

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...

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:

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

UW Hydromet Domain basins ~60 USGS Gauge Locations 48,896 km 2 2,173,155 pixels 150 m resolution 4 & 12 km

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

Performance of Hydromet System MM5-DHSVM Observed NWRFC SaukSnoqualmie

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 Of, course, not all forecasts were so bad…

Representative Meteorological Station – Mt. Gardner Avg. Precipitation from 1/24 - 2/7: Observed: 1.0 mm/h Simulated: 0.7 mm/h Total difference: ~100 mm Precip 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

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.

Use ground observations (SNOTEL sites) to adjust the basin snow state Challenge: snow water observations for 48,000 km 2 domain – low density places high dependence on interpolation assumptions Snow State Updating with Observations

Expansion of Forecast Products Source: Grimit and Eckel, 2003 Probabilistic streamflow forecasts ‑Take advantage of ensemble MM5 simulations to estimate uncertainty in forecasts 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

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

Acknowledgments

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 balance estimates)

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