Daily Estimates of Global Radiation in the Brazilian Amazon by Simplified Models

Solar radiation is an element and a meteorological factor that is present in several processes, such as evapotranspiration, photosynthesis, and energy generation, among others. However, in some regions, there is a limitation in surface data measurements. In this study, 87 empirical models were evaluated to estimate global radiation (Hg) in the Brazilian Amazon Biome; these models were divided into five groups according to the input variables, such as insolation (group I), air temperature (group II), relative humidity (group III), astronomical variables (group IV), and hybrid models (group V) as input variables. The estimates were evaluated by their significance (t-test) and then according to the statistical metrics of the models' performance (R2, MBE, RMSE, and d). The group V model [Hg/Ho = a + b lnΔT + c (S/So)d)] presented the best statistical performance in all evaluated indicators, followed by the group I model [Hg/Ho = a + b (S/So)c ] and then the group II model [Hg/Ho = a + bΔT + c ΔT0.25 + d ΔT0.5 + e (Tmed/Ho)]. The group III models presented low statistical performance, and the group IV models were not significant (NS) in all evaluated meteorological stations. In general, it was found that the simple or hybrid models based on insolation and air temperature were efficient in estimating Hg in the Brazilian Amazon Biome.