2006 Water Resources Outlook for Idaho and the Western U.S. JISAO Center for Science in the Earth System Climate Impacts Group and Department of Civil and Environmental Engineering University of Washington October, 2006 http://www.hydro.washington.edu/Lettenmaier/Presentations/2004/hamlet_2006_forecast_oct_2005.ppt Alan F. Hamlet Andy Wood Dennis P. Lettenmaier

Background

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 25th 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

Background: Hydrology Model

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 important point(s): the approach attempts to make use of forecast skill from 2 sources: better understanding of synoptic scale teleconnections and the effects of persistence in SSTs on regional climate, as reproduced in coupled ocean-atmosphere models; the macroscale hydrologic model yields an improved ability to model the persistence in hydrologic states at the regional scale (more compatible with climate model scales than prior hydrologic modeling). Climate forecasts with monthly and seasonal horizons are now operationally available, and if they can be translated to streamflow, then they may be useful for water management.

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

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

Recap of Water Year 2005

Observed Nino3.4 anomally

Natural Flows at Milner 1928-1989

Simulated Natural Flow at Milner (Oct ESP Nino3.4 between +0.2 and +1.2) (data from 1960-2002 period) Natural Streamflow (KAF) WY 2005

http://www. hydro. washington http://www.hydro.washington.edu/forecast/westwide/archive/spatial/columbia.shtml

http://www. hydro. washington http://www.hydro.washington.edu/forecast/westwide/archive/spatial/columbia.shtml

Probability of Exceedence Plot for Natural Flow at Milner from WY 2005 Forecast

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. October 1 Spin Up Active Reservoir Storage (kaf) Obs. System Storage Oct 1, 2005

Outlook for Water Year 2006

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

http://www.hydro.washington.edu/forecast/westwide/

Initial Soil Moisture Conditions Oct 1, 2004

UW West Wide Seasonal Hydrologic Forecast System http://www.hydro.washington.edu/forecast/westwide/sflow/index.shtml

UW West Wide Seasonal Hydrologic Forecast System http://www.hydro.washington.edu/forecast/westwide/sflow/index.shtml

Used range: Jan3.4 >= -0.4 Jan3.4 <= 0.6

Used range: Jan3.4 >= 0.0 Jan3.4 <= 0.6

Natural Flows at Milner 1928-1989

Natural Streamflow (KAF) Climatology of Naturalized Streamflow in the Snake River at Milner Milner Climatology 1928-1992 Natural Streamflow (KAF)

Natural Streamflow (KAF) Red = long term mean Blue = ensemble mean Gray = ensemble members Black = range of observations WY 2006

Natural Streamflow (KAF) Red = long term mean Blue = ensemble mean Gray = ensemble members Black = range of observations

PDO ENSO Forecast for Milner Assuming “Neutral PDO Years” And Nino3.4 between -0.4 and 0.6 Natural Streamflow (KAF)

System Storage Forecast from SnakeSim: Jackson Lake Palisades Island Park Ririe American Falls Lake Walcott Nino3.4 anomaly between -0.4 and 0.6 C Demand aligned with water cond. October 1 Spin Up Active Reservoir Storage (kaf)

Summary of 2006 Forecast Current soil moisture on Oct, 2005 is relatively wet in southern Idaho, and relatively dry in northern Idaho. ENSO neutral conditions are likely in WY 2006, with forecast Nino3.4 anomalies ranging from about 0.0 to 0.6 in mid winter. Probability distributions for streamflow in ENSO neutral years are similar in character to the climatology overall. The central tendency of the WY 2006 streamflow forecast at Milner is near the long term mean for both ENSO and PDO/ENSO composites. Risks of very high or very low flows are somewhat reduced, but very high and low flow events have occurred for similar ENSO/PDO conditions in the past. Carryover storage in the upper Snake reservoirs is improved from last year, and the reservoir system forecast suggests peak reservoir storage levels of about 3000 KAF in April or May, 2006, and carryover storage in Sept, 2006 of about 1000 KAF.

Climate Change Planning Activities Snake River Planning Data Resources Weekly time step surrogate observations and climate change streamflow scenarios for the Snake basin are currently available: ftp://ftp.hydro.washington.edu/pub/hamleaf/snakesim/ USBR planning study for the Flathead Draft daily flow scenarios are completed Preliminary reservoir model analysis in progress New GCM Scenarios from the IPCC 4th Assessment CIG Climate Change Reports and White Papers for King Co. Planning Meeting and Puget Sound Action Team

Overview of Experimental Energy-Related Forecasting Products

Covariation of Normalized PNW and CA Hydropower Production California hydropower is less than 10% of total CA demand, but may play a significant role in energy trading on short time scales.

Probability of Exceedance for Spring Surplus Energy Resources in the PNW Voisin, N., A. F. Hamlet, L. P. Graham, D. W. Pierce, T. P. Barnett, and D. P. Lettenmaier, 2005: The role of climate forecasts in western U.S. power planning, Journal of Applied Meteorology (accepted).