1. Alan F. Hamlet Andy Wood Dennis P. Lettenmaier JISAO Center for Science in the Earth System Climate Impacts Group and Department of Civil and Environmental Engineering University of Washington October, 2004 2005 Water Resources Outlook for Idaho and the Western U.S. http://www.hydro.washington.edu/Lettenmaier/Presentations/2004/hamlet_2005_forecast_oct_2004.ppt

2. Background

3. Background: Forecast System Schematic NCDC met. station obs. up to 2-4 months from current local scale (1/8 degree) weather inputs soil moisture snowpack Hydrologic model spin up SNOTEL Update streamflow, soil moisture, snow water equivalent, runoff 25 th Day, Month 0 1-2 years back LDAS/other real-time met. forcings for spin-up gap Hydrologic forecast simulation Month 6 - 12 INITIAL STATE SNOTEL / MODIS* Update ensemble forecasts ESP traces (40) CPC-based outlook (13) NCEP GSM ensemble (20) NSIPP-1 ensemble (9) * experimental, not yet in real-time product

4. Seasonal Climate Forecast Data Sources ESP ENSO/PDO ENSO CPC Official Outlooks Seasonal Forecast Model (SFM) CAS OCN SMLR CCA CA NSIPP-1 dynamical model VIC Hydrolog y Model NOAA NASA UW

5. Background: Hydrology Model

6. Background: Estimating Initial Conditions SNOTEL assimilation Assimilation Method weight station OBS’ influence over VIC cell based on distance and elevation difference number of stations influencing a given cell depends on specified influence distances spatial weighting function elevation weighting function SNOTEL/ASP VIC cell distances “fit”: OBS weighting increased throughout season OBS anomalies applied to VIC long term means, combined with VIC-simulated SWE adjustment specific to each VIC snow band

7. Framework: Estimating Initial Conditions snow cover (MODIS) assimilation (Snake R. trial) Snowcover BEFORE update Snowcover AFTER update MODIS update for April 1, 2004 Forecast snow added removed

8. Background : Streamflow Forecast Locations in development: Colorado R., Upper Rio Grande Columbia R. basin California Snake R. basin

9. Linkage to Reservoir Models Streamflow Forecast Bias Correction Reservoir Model Observed Reservoir Contents Storage Ensemble Demand Scenarios

10. ColSim Storage Forecast

11. Recap of Water Year 2004

12. Initial Conditions for Winter 2003-04 Soil Moisture and Snow Water Equivalent (SWE)

13. Initial Conditions for Winter 2003-04 Soil Moisture and Snow Water Equivalent (SWE)

14. Initial Conditions for Winter 2003-04 Soil Moisture and Snow Water Equivalent (SWE)

15. Initial Conditions for Winter 2003-04 Soil Moisture and Snow Water Equivalent (SWE)

16. Initial Conditions for Winter 2003-04 Soil Moisture and Snow Water Equivalent (SWE)

17. Winter 2003-04: PNW streamflow By Fall, slightly low flows were anticipated By winter, moderate deficits were forecasted

18. Winter 2003-04: seasonal volume forecasts Comparison with RFC forecast for Columbia River at the Dalles, OR UW forecasts made on 25 th of each month RFC forecasts made several times monthly: 1 st, mid-month, late (UW’s ESP unconditional and CPC forecasts shown) UW RFC

19. Last winter: volume forecasts for a sample of PNW locations

26. Evaluation of Last Year’s ColSim Storage Forecast Obs.Sys Storage Sept 15, 2004

27. System Storage Forecast from SnakeSim: Jackson Lake Palisades Island Park Ririe American Falls Lake Walcott 11 ENSO neutral years (reshuffled 3 times) Random historic demand scenarios Full Pool Active Reservoir Storage (kaf) Green = ensemble mean Obs. Storage Sept 30, 2004

28. Outlook for Water Year 2005

29. December Winter Climate Forecasts Dominate Hydrologic State Variables Dominate JuneMarch Range =16.7% of ensemble summer mean April 1 SWE (mm)

30. Initial Soil Moisture Conditions

34. Natural Flows at Milner 1928-1989

35. Simulated Natural Flow at Milner (Oct ESP Nino3.4 between +0.2 and +1.2)

36. Upper Snake Storage Climatology Storage Sept 30, 2004 Historic water years 1928-1992

37. October 1 Spin Up System Storage Forecast from SnakeSim: Jackson Lake Palisades Island Park Ririe American Falls Lake Walcott Nino3.4 anomaly between 0.2 and 1.2 C Demand aligned with water cond. Active Reservoir Storage (kaf)

38. Impacts of the West-Wide Drought on the Pacific Northwest

39. 1930s Drought Soil Moisture 80 Percent severity 100 Soil moisture-defined drought Figure courtesy of Elizabeth Clark and Kostas Andreadis, UW

40. Current Drought Soil Moisture Soil moisture-defined drought 80 Percent severity 100 Figure courtesy of Elizabeth Clark and Kostas Andreadis, UW

41. Concluding Remarks Soil moistures in Oct, 2004 are wetter overall in comparison with Oct, 2003. Drought risks appear to be about the same as last year based on likely mid-winter Nino3.4 anomalies, and the highest likelihood is for flows clustered around normal conditions (very high and very low flows unlikely). However, one very high and one very low flow year have both occurred for this range of Nino3.4 anomalies, so both extremes cannot be ruled out. The wild card is the West-wide drought. If the large scale climate anomaly that has impacted precipitation over the west continues to impinge on southern Idaho, analogue years based on Nino3.4 anomalies may not be very representative. Will the drought continue, and will it impact Idaho if it does?