Models and Calibratio n

1. Models and Calibration CBRFC 2011 Stakeholder Forum November 3, 2011

2. CBRFC Forecast Groups White Yampa

3. White Yampa Basin ENMC2

4. White Yampa - Elk near Milner (ENMC2)

5. White Yampa - Elk near Milner (ENMC2) Upper (10000-11970) Middle (8500-10000) Lower (7205-8500)

6. Calibrations/Simulations - inputs • In reality the 3 areas (upper, middle and lower) are represented (simulated) by only 3 points (Lumped Model) • The inputs our model needs for calibrations and operations (at these 3 points) are: • precipitation • temperature • freezing level

7. For Elk River at Milner (ENMC2) ENMC2 upper area Elevation = 10569 ft Area = 64 sqmi ENMC2 middle area Elevation = 9146 ft Area =159 sqmi ENMC2 lower area Elevation = 7692 ft Area =246 sqmi

8. Calibrations/Simulations - Precipitation • Each area (upper, middle and lower) MAP is built using precipitation stations that (hopefully) have similar characteristics to that area • For the ENMC2 • Upper area – DRLC2 .46, ELKC2.46 • Middle area - DRLC2 .46, ELKC2.46 • Lower area - DRLC2 .46, ELKC2.46 • These weights were chosen to guarantee water balance in each area. The water balance in each area was calculated using the PRISM sets

9. White Yampa - Elk near Milner (ENMC2) Precipitation Gages

10. Calibrations/Simulations - Temperature • Nearby stations (whose climatology is known) area used to calculate the temperature at the mid-point elevation of the area (whose climatologies are calculated using the climatology of the nearby stations) • Temperature is calculated by using the difference in station and area climatology • For the ENMC2 • Upper area – CRSC2 0.009, ELKC2 0.011 • Middle area - SBTC2 0.009, CRSC2 0.013, ELKC2 0.045 • Lower area - WBSW4 0.009, SBTC2 .02,HAYC2 0.013, ELKC2 0.019

11. White Yampa - Elk near Milner (ENMC2) Temperature Gages

12. Calibrations/Simulations - Inputs • Precipitation and temperature are calculated every six hours at each area within the basin • 30 year historical record calculation • Used to calibrate hydrologic models • Operationally done in a similar way • Ensures our forecasts will have similar quality/characteristics to calibration • For the Elk at Milner this is done for the upper, middle and lower areas

13. Calibrations/Simulations - Models • A snow model is first run for each area in the basin • accumulates/ablates snow • A soil moisture model is then run for each area • Controls amount of water from the snow model • retained in the soil • evaporates or • ends up in the stream • Evaporation is a calibrated amount: • E=P-Q

14. Snow Cover Heat Deficit Snow Cover Outflow Rain plus Melt Accumulated Snow Cover Precipitation and Air Temperature Bare ground or snow cover Rain or Snow SNOW ACCUMULATION AND ABLATION MODEL (SNOW-17) Energy Exchange at Snow-Air Interface Areal Extent of the Snow Cover Deficit = 0 Liquid Water Storage Rain on Bare Ground Ground Melt Transmission of Excess Water

15. Sacramento Soil Moisture Accounting Model TENSION WATER STORAGE DIRECT RUNOFF UPPER ZONE FREE WATER STORAGE SURFACE RUNOFF INTERFLOW LOWER ZONE PRIMARY FREE WATER STORAGE TENSION WATER STORAGE TENSION WATER STORAGE SUPPLEMENTARY FREE WATER STORAGE BASEFLOW SUBSURFACE OUTFLOW

16. Calibrations - Results

17. Simulations - Real Time (no mods)

18. Simulations - Results (with mods)

20. Calibrations/Simulations - Reservoirs • Reservoir modeling is difficult as they are not physically based. However, we calibrate the reservoir models assuming two different modes: • Irrigation (use average releases) • Spillway/passflow • Operationally we can do the following: • Assume the current release • Input a schedule • Allow the spill/passflow rules

21. Reservoir Calibrations

22. Reservoir Simulations – Assume Constant Outflow

23. Reservoir Simulations – Use Rules

24. Reservoir Simulations – Use Rules

25. Reservoir Simulations – Release Schedule

26. Adjustments to Flow • Unregulated flow = Observed flow + Diversions (measured) + Storage • Natural flow = Unregulated flow + Consumptive Use • Consumptive use (in basin irrigation) can only be estimated • In our simulations, we simulate natural flow but subtract out the consumptive use so the output is always unregulated flow • So: • We simulate “natural flow” • We remove the in-basin irrigation (consumptive use) • This is the simulated unregulated flow. It simulates the actual flow plus the measured diversions (adjusted flow) • Operational considerations • Observed flow = Unregulated flow - Diversions - Storage

27. http://www.cbrfc.noaa.gov/wsup/doc.php

28. Calibrations/Simulations • 463 basins • 1139 sub areas (1-3 per basin) • 88 reservoirs • 22 routes (no snow model or soil model)

29. Recalibration • 30 year averages are updated once every 10 years • WY2011 Used: • 1971-2000 for averages • 1971-2000 for statistical prediction • 1976-2005 for ESP • Update for WY2012 will be based on 1981-2010 time series • New averages based on 1981-2010 • New statistical prediction equations based on 1981-2010 period • Recalibration of 463 river basin models to the 1981-2010 period • Better effort made to create MAP and MAT time series • CBRFC will debut all of this for January 2012 forecasts

30. Preliminary Data • 18% reduction in mean

31. Effect on Forecasts • WY2012 forecasts will be based on 1981-2010 inputs in both forecast models • ESP and SWS will both use the same period • SNOTEL network much stronger for 1981-2010 period than in 1970s. This network is critical for forecast skill. • All things equal, these forecasts will be lower since input data sets are drier in the 30 year average • Especially true in early season forecasts • Later season forecasts more controlled by observed snowpack • Percent of normal forecast values should remain largely unchanged (since normals AND forecasts will be lower)

32. Example: ESP forecastsMean influence to early season forecasts somewhat less

33. Example: ESP forecastsMean influence to late season forecasts small

34. Questions