A solar radiation model for use in biological applications in the South and Southeastern USA

The application of a previously developed stochastic solar radiation model, the Hedges model (Hedges, T,, French, V, and LeDuc, S,, 1985. Estimating solar radiation for plant simulation models, AgRISTARS Technical Report JSC-20239; YM-15-00403, 21 pp.) was modified using the Solar and Meteorological Surface Observation Network (SAMSON) data base, Model parameters were re-estimated and a geographic stratification scheme was developed that more accurately reflects climatologic variability in radiation on rainy and on dry days, Daily solar radiation from the model was adjusted further to reflect observations at 59 sites throughout the South and Southeastern USA based on the average and the standard deviation, Errors in averages and standard deviations of model estimates made while using this modified application approach were summarized. Estimates of average model output for all days, wet days only or dry days only were within 10% of SAMSON estimates, Standard deviation estimates were also within 10%. The impact of this modified application approach on corn yield estimated with the Erosion/Productivity Impact Calculator (EPIC) crop simulation model was examined at a sample location in North Carolina. Yield estimates generated using the original application approach, the modified approach and the existing EPIC solar radiation generator were compared. Each method of radiation estimation produced yield time series that were significantly different from one another in a pair-wise comparison. Using data for 1961 through 1988, a further comparison of yield time series indicated that the Hedges model used with the application modifications suggested by this research provided a superior estimate of daily radiation.