Submitted to: Journal Hydrologic Engineering
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/12/2008
Publication Date: 3/1/2009
Citation: Jacobs, J., Lowery, B., Choi, M., Bolster, C.H. 2009. GOES Solar Radiation for Evapotranspiration Estimation and Streamflow Predictions. Journal Hydrologic Engineering. 14(3):293-300. Interpretive Summary: The National Weather Service River Forecast System (NWSRFS) uses the Sacramento Soil Moisture Accounting (SAC-SMA) model to generate river and flood forecasts across the U.S. One of the required inputs needed to run SAC-SMA is potential evapotranspiration (PET), which the NWSRFS computes using the Penman combination equation in the Synoptic Data Transfer (SYNTRAN) utility program. Of the meteorological data required to compute PET, incoming solar radiation data availability is the greatest challenge for operational hydrologic applications. Total sky cover observations, which SYNTRAN uses to estimate incoming solar radiation, have been phased out of existence with the implementation of the Automated Surface Observation System (ASOS). Therefore, NWS needs to find solar radiation data sets to replace the SYNTRAN solar radiation data without diminishing SAC-SMA model accuracy during streamflow simulations. We use Geostationary Operational Environmental Satellite (GOES) girded solar radiation and meteorological forcing data from the Distributed Model Intercomparison Project (DMIP) test basins to calculate the PET estimates needed to simulate streamflow with the SAC-SMA model. Resultant daily streamflow predictions are compared with observed streamflow data.
Technical Abstract: The National Weather Service River Forecast System uses the Sacramento Soil Moisture Accounting (SAC-SMA) rainfall-runoff model to produce daily river and flood forecasts and issue flood warnings. The manual observations of total sky cover used to estimate solar radiation and potential evapotranspiration in the SAC-SMA model, however, have recently been phased out. This study explores the value of incoming solar radiation estimates derived from Geostationary Operational Environmental Satellites (GOES) as an alternative solar radiation data source. At twenty-seven sites in the United States, the GOES-based solar radiation (R2 = 0.79) and ETp (R2 = 0.94) estimates agreed well with the ground-based estimates. There was a slight positive bias for the GOES-based solar radiation (7%) and potential evapotranspiration (11%) estimates compared to the ground-based estimates, with the strongest bias noted during the warm seasons. Daily streamflow predictions from four watersheds from the NOAA Distributed Model Intercomparison Project (DMIP) show that although notable peak storm flow differences occurred occasionally during extended drying periods, on average, the GOES-based potential evapotranspiration estimates slightly outperformed the simulations using ground-based data. This suggests that satellite-derived solar radiation data are capable of producing accurate predictions of streamflow with the SAC-SMA model.