1 Department of Natural Sciences, Department of Basic Sciences and Environment, Faculty of Life Sciences, Københavns Universitet2 Department of Agriculture & Ecology, Environment, Resources and Technology, Department of Agriculture & Ecology, Faculty of Life Sciences, Københavns Universitet3 Oregan State University4 Est. Expt. Aula Dei (CSIC)5 CIFA Alameda del Obispo6 unknown7 Section for Environmental Chemistry and Physics, Department of Plant and Environmental Sciences, Faculty of Science, Københavns Universitet8 Department of Agriculture & Ecology, Environment, Resources and Technology, Department of Agriculture & Ecology, Faculty of Life Sciences, Københavns Universitet9 Department of Natural Sciences, Department of Basic Sciences and Environment, Faculty of Life Sciences, Københavns Universitet10 Section for Environmental Chemistry and Physics, Department of Plant and Environmental Sciences, Faculty of Science, Københavns Universitet
Daily values of net radiation are used in many applications of crop-growth modeling and agricultural water management. Measurements of net radiation are not part of the routine measurement program at many weather stations and are commonly estimated based on other meteorological parameters. Daily values of net radiation were calculated using three net outgoing long-wave radiation models and compared to measured values. Four meteorological datasets representing two climate regimes, a sub-humid, high-latitude environment and a semi-arid mid-latitude environment, were used to test the models. The long-wave radiation models included a physically based model, an empirical model from the literature, and a new empirical model. Both empirical models used only solar radiation as required for meteorological input. The long-wave radiation models were used with model calibration coefficients from the literature and with locally calibrated ones. A measured, average albedo value of 0.25 was used at the high-latitude sites. A fixed albedo value of 0.25 resulted in less bias and scatter at the mid-latitude sites compared to other albedo values. When used with model coefficients calibrated locally or developed for specific climate regimes, the predictions of the physically based model had slightly lower bias and scatter than the empirical models. When used with their original model coefficients, the physically based model had a higher bias than the measurement error of the net radiation instruments used. The performance of the empirical models was nearly identical at all sites. Since the empirical models were easier to use and simpler to calibrate than the physically based models, the results indicate that the empirical models can be used as a good substitute for the physically based ones when available meteorological input data is limited. Model predictions were found to have a higher bias and scatter when using summed calculated hourly time steps compared to using daily input data.
Journal of Theoretical and Applied Climatology, 2009, Vol 98, Issue 1-2, p. 57-66