Space-time scale sensitivity of the Sacramento model to radar-gage precipitation inputs

Runoff timing and volume biases are investigated when performing hydrologic forecasting at space-time scales different from those at which the model parameters were calibrated. Hydrologic model parameters are inherently 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 networks. The space-time scale sensitivity of the Sacramento model runoff volume is analyzed using I-hour, 4 x 4 km(2) next generation weather radar (NEXRAD) precipitation estimates to derive input MAPs at various space-time scales. Continuous simulations are run for 9 months for time scalps 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 supplemental baseflow runoff components are the most sensitive to the space-time scales analyzed. Water balance components of evapotranspiration and total channel inflow are also sensitive. A preliminary approach for adjusting model parameters to account for spatial and temporal variation in rainfall input is presented. (C) 1997 Published by Elsevier Science B.V.