In the current study, the ability of three data-driven methods of Gene Expression Programming (GEP), M5 model tree (M5), and Support Vector Regression (SVR) were investigated in order to model and estimate the dew point temperature (DPT) at Tabriz station, Iran. For this purpose, meteorological parameters of daily average temperature (T), relative humidity (RH), actual vapor pressure (V_p), wind speed (W), and sunshine hours (S) were obtained from the meteorological organization of East Azerbaijan province, Iran for the period 1998 to 2016. Following this, the methods mentioned above were examined by defining 15 different input combinations of meteorological parameters. Additionally, root mean square error (RMSE) and the coefficient of determination (R²) were implemented to analyze the accuracy of the proposed methods. The results showed that the GEP-10 method, using three input parameters of T, RH, and S, with RMSE of 0.96°, the SVR-5, using two input parameters of T and RH, with RMSE of 0.44, and M5-15, using five input parameters of T, RH, V_p, W, and S with RMSE of 0.37 present better performance in the estimation of the DPT. As a conclusion, the M5-15 is recommended as the most precise model in the estimation of DPT in comparison with other considered models. As a conclusion, the obtained results proved the high capability of proposed M5 models in DPT estimation.

A fundamental factor for proficient designing of solar energy systems is providing precise estimations of the solar radiation. Global solar radiation (GSR) is a vital parameter for designing and operating solar energy systems. Because records of GSR are not available in many places, especially in developing countries, this research aims to model the GSR using support vector regression (SVR) in a hybrid manner that is integrated with the firefly Optimization algorithm (SVR-FFA). For this purpose, the daily meteorological parameters and GSR measured from beginning of 2011 to the end of 2013 at Tabriz synoptic station were utilized. For assessing the performance of the mentioned methods, different statistical indicators were implemented. For all of the defined predictive models with different combinations of meteorological parameters, the performance of the SVR-FFA hybrid model is better than the classical SVR, evidenced by the higher value of R (~0892-0.982 relative to ~0.891-0.977) and lower values of RMSE and MAE (~1.551-3.725vs.1.748-4.067 and ~0.911-2.862vs.1.103-2.742). As a remarkable point studied empirical equations had higher prediction errors comparing with the developed SVR-FFA models. Conclusively, the obtained results proved the high proficiencies of SVR-FFA method for predicting global solar radiation.