HR: 09:15h
AN: H21H-06    [Abstracts]
TI: Implementing Probabilistic Climate Outlooks Within a Seasonal Hydrologic Forecast System
AU: * Wood, A W
EM: aww@hydro.washington.edu
AF: University of Washington, Civil and Env. Engineering Box 352700, SEattle, WA 98195-2700 United States
AU: Lettenmaier, D P
EM: lettenma@ce.washington.edu
AF: University of Washington, Civil and Env. Engineering Box 352700, SEattle, WA 98195-2700 United States
AB: We describe a method for implementing the Climate Prediction Center's probabilistic climate outlooks within an experimental ensemble hydrologic forecast system. The forecast system has been developed for the portion of the U.S. and the Canadian portion of the Columbia River basin west of the Continental Divide. Forecasts are made at lead times of six months to a year, using the Variable Infiltration Capacity (VIC) macroscale hydrology model implemented at 1/8 degree spatial resolution. Ensemble forecasts are derived from historical resampling, global climate model ensemble forecasts, and most recently the CPC Official Seasonal Outlooks, formulated as probability of exceedence (POE) distributions for temperature and precipitation, using the climate division as the spatial unit. Our current approach for downscaling the CPC POE forecasts involves a resampling step (called the "Schaake Shuffle", as described in a recent paper by M. Clark and others) that is applied to create a 13-member ensemble (of monthly timeseries of precipitation and temperature for each Climate Division) that exhibits plausible spatial and temporal structure. A subsequent resampling step is applied to disaggregate timeseries from a monthly to a daily timestep, and from the climate division to the 1/8 degree hydrologic model grid scale. In this talk, we address two questions: 1) whether the downscaling approach reproduces the observational mean and variability for streamflow, and for spatial temperature and precipitation fields; and 2) whether bias-correction of the climate division POE forecasts is a necessary step in the downscaling process. These questions were investigated through the application of the downscaling approach to the CPC retrospective observational climate division dataset, and via comparisons with a climate division unit dataset aggregated from the authors' PRISM-corrected retrospective climatology.
DE: 1833 Hydroclimatology
DE: 1854 Precipitation (3354)
DE: 1860 Runoff and streamflow
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting