SPACE-TIME SCALE SENSITIVITY OF THE SACRAMENTO MODEL TO RADAR-GAUGE PRECIPITATION INPUTS

Runoff timing and volume biases are investigated when performing hydro logic forecasting at space-time scales different from those at which t he model parameters were calibrated. Hydrologic model parameters are i nherently tied to the space-time scales at which they were calibrated. The National Weather Service calibrates rainfall runoff models using 6-hour mean areal precipitation (MAP) inputs derived from gage network s. The space-time scale sensitivity of the Sacramento model runoff vol ume is analyzed using I-hour, 4 x 4 km(2) next generation weather rada r (NEXRAD) precipitation estimates to derive input MAPs at various spa ce-time scales. Continuous simulations are run for 9 months for time s calps of 1, 3, and 6 hours, and spatial scales ranging from 4 x 4 km(2 ) up to 256 x 256 km(2). Results show surface runoff, interflow, and s upplemental baseflow runoff components are the most sensitive to the s pace-time scales analyzed. Water balance components of evapotranspirat ion and total channel inflow are also sensitive. A preliminary approac h for adjusting model parameters to account for spatial and temporal v ariation in rainfall input is presented. (C) 1997 Published by Elsevie r Science B.V.