Seasonal Volume Forecasts Using Ensemble Streamflow Prediction for the 2008 Water Year Steve King, Hydrologist Northwest River Forecast Center

Topics for Presentation  Northwest River Forecast Center:  Overview  NWRFC Long Range Forecasting Models and Products  Statistical Water Supply Forecasts  Ensemble Streamflow Prediction (ESP)  Recap of WY 2007 Forecasts  2008 Volumetric Streamflow Outlook  New Web Tools for Users

Northwest River Forecast Center Total Area: 315,795 Grand Coulee Dam The Willamette at Salem The Dalles Dam Lower Granite Dam Columbia and Snake River Basins Coastal Drainages of Oregon and Washington 6 States & CANADA Support for 9 NWS Field Offices (WFOs)

NWRFC Forecasting Models  Statistical Water Supply  Seasonal Volumetric Forecasts Regression techniquesRegression techniques 168 forecast locations168 forecast locations  NWS River Forecast System  Short, Medium, and Longterm capabilities Generates output in deterministic AND probabilistic (ESP) formatsGenerates output in deterministic AND probabilistic (ESP) formats Variable Outputs for ESPVariable Outputs for ESP

Statistical Water Suppy Combined Index: Observed Precip Observed Snow Observed Runoff Future Precip

Snow Model Soil Moisture/Runoff Consumptive Use River Routing Reservoir Regulation Flow and Stage Forecasts NWS River Forecast System Model Components (simplified) Rain Plus Snow Melt

NWS River Forecast System

Exceedance probability plot of flow volumes = area under each trace (Jan-Jul period) 50% Value (most expected) is comparable to WS forecasts Example showing 42 traces outcomes for The Columbia River at The Dalles, OR Runtime conditions: 9/13/2004 Analysis period: 1/1/2005-8/1/2005 Traces represent ensemble of possible river flow behavior (Jan-Jul) Median Forecast (most expected) ESP

Volume Forecasts Available at Statistical Water Supply ESP Volume Forecasts

2007 WS Forecast Recap ( Jan-Jul ‘07) Jan-Jul Volume Forecasts Jan-Jul Volume 30 yr Normal 63 MAF 2007 Jan-Jul Obs Volume 63.9 MAF 102% 2006 Fall ESP Outlook 60.6 MAF

2007 WS Forecast Recap (Jan-Jul ‘07) Jan-Jul Volume Forecast Jan-Jul Volume 30 yr Normal 107 MAF 2007 Jan-Jul Obs Volume 95.7 MAF 89% 2006 Fall ESP Outlook MAF

2007 WS Forecast Recap (Apr-Sep ‘07) Apr-Sep Volume Forecast Apr-Sep Volume 30 yr Normal 1.92 MAF 2007 Apr-Sep Obs Volume 1.48 MAF 77% 2006 Fall ESP Outlook 1.82 MAF

Spring Outlook  Ensemble Streamflow Prediction (ESP)  Driven by: Antecedent Snow/Soil Moisture 10 day Precip and Temp Forecast  Updated weekly  Capability of including climate forecasts/signals  Not included in current published versions

2008 Outlook (ESP Forecasts) 60.8 MAF 97% of Normal (63 MAF) MAF 96 % of Normal (107 MAF)

 ESP Pre Adjustment Technique:  CPC Outlooks are used to shift distribution of model inputs (temperature and precipitation) Taking Advantage of Climate Forecasts:

2007 Aug SOI = 0.1 Jun-Aug = Taking Advantage of Climate Forecasts:  ESP Post Adjustment Technique: Year Weights

Comparison of ESP 2008 with ESP Climate Adjusted

New Web Tool

New Volumetric Forecast Display Tool New Web Tool Late Fall 2007

New Web Tool Late Fall 2007

New Web Tool Late Fall 2007

Climate Change Scenarios Climate Change runoff scenarios? Years New Web Tool Precipitation Scenarios 9 Temperature Scenarios

Climate Change Scenarios Arbitrary changes to basin temperature and precipitation imposed on forcing time series (e.g. 0.2 F / year in example above) New Web Tool 2008

Climate Change Scenarios (Con’t) Produces hydrologic scenarios Ensembles generated by “wrapping” years New Web Tool 2008

Northwest River Forecast Center Portland WFO/ Northwest River Forecast Center OPEN HOUSE Oct 6 th, 2007