UW Hydrologic Forecasting: Yakima R. Discussion Andy Wood and Dennis P. Lettenmaier Department of Civil and Environmental Engineering for Washington State Drought Task Force Olympia, WA April 25, 2005

Presentation Outline 1. UW Experimental Hydrologic Forecasting System 2. Water Year 2005 Assessment for Yakima R. above Parker

UW Experimental Hydrologic Forecasting System funded by Objective: To create a model-based testbed for evaluating potential sources of improvement in seasonal forecasts since inception of regression/ESP methods operational seasonal climate forecasts (model-based and otherwise) greater real-time availability of station data computing advances new satellite-based products (primarily snow cover) distributed, physical hydrologic modeling for macroscale regions

UW Forecasting: Model used to estimate conditions Snowpack Initial Condition Soil Moisture Initial Condition

UW Forecasting: SNOTEL merged with model SWE The pattern of observed SWE values, which are merged with the forecast initial conditions, is generally in good agreement with the VIC simulated snow state. The PNW currently has had near record low snowpacks, while the Southwest and California have had record high snowpacks.

UW Forecasting: Streamflow simulations calibrated VIC model runoff is routed to streamflow gages, and verified against observations

UW Forecasting: Sample Streamflow ‘Products’ locations monthly hydrographs targeted statistics e.g., runoff volumes

UW Forecasting: Sample Spatial Forecasts Precip Temp SWE Runoff Soil Moisture Mar-05 Apr-05 May-05

Comments on Yakima Basin forecasts 1. We do not yet have calibrated streamflow forecasts for the Yakima R. basin, but have started working on 3 gages (more are possible). 2. We have water-balance forecasts produced by averaging variables over the model grid cells in the basin. 3. Without full model calibration, these are best used for seasonal (summer) runoff (hence streamflow) forecasts, since the weekly/monthly timing may not be accurate. 12479500 Yakima R. at Cle Elum 12494000 Naches R. at Naches 12505000 Yakima R. nr. Parker

Presentation Outline 1. UW Experimental Hydrologic Forecasting System 2. Water Year 2005 Assessment for Yakima R. above Parker - April 1, Western US conditions - April 15, conditions for PNW only - basin-averaged forecasts for Yakima R. near Parker, WA

WY2005, Apr. 1 hydrologic conditions

WY2005, Apr. 15 hydrologic conditions Snow Water Equivalent (Yakima nr Parker basin highlighted) value (mm) % of normal percentile

WY2005, Apr. 15 hydrologic conditions Soil Moisture (Yakima nr Parker basin highlighted) note: it appears headwaters have elevated SM, perhaps from recent early melt value (mm) % of normal percentile

4/15 ESP forecast: WY2005 Precip, Temp plots show current + forecast (ESP; min, max and quartiles) against historical 1971-2000 min, max and quartiles Yakima R. Basin near Parker, WA

4/15 ESP forecast: WY2005 SM, SWE, RO Apr-Sep % of avg 3/15 4/15 chg max 61 57 0.75 46 50 0.50 41 45 0.25 39 42 min 31 39

Forecast Summary ESP forecast is ~50% chance of 42-50% of normal summer runoff. Precip. has fed SM and runoff instead of snow, so Jun-Jul-Aug. will be hit worse than Apr-May. Situation has improved since 1 month ago, slightly: forecast median hasn’t changed much but the lowest forecasts from 1 month ago are no longer possible. Snowpack state is extremely low, but soil moisture appears to be near or slightly above normal, which will offset the effects of the low snowpack in the near term.

Questions? website: www.hydro.washington.edu / Lettenmaier / Projects / fcst / contact: Andrew Wood Research Assistant Professor Dept. Civil and Environmental Engineering Hydrology and Water Resources 206-543-5856 aww@u.washington.edu