Modification of the radiation-based Abtew reference evapotranspiration model under humid climate, Northeast India

In this work, seven models of temperature-based solar radiation were used to enhance the Abtew model for ET0 calculation in Northeast India. The only input data needed for the temperature-based models are air temperature, which can be easily measured in most locations worldwide. Under the climatic conditions of Dibrugarh, Northeast India, the applicability of the improved Abtew models (A1-A7), the Stephen-Stewart model (SS), the Irmak model (Ir), and the Modified Turc model (MT) was assessed. Utilizing statistical indices such as mean absolute error (MAE), root-mean-square error (RMSE), standard error (SE), coefficient of correlation (r), coefficient of determination (R-2), and index of agreement (D), the performances of all the modified equations (A1-A7) and other chosen ET0 models have been compared. The findings demonstrated that for ET0 estimate at Dibrugarh, the seven upgraded Abtew models (RMSE = 0.44-0.50 mm/day; D = 0.81-0.88) outperformed the four physical models (RMSE = 0.50-2.77 mm/day; D = 0.49-0.82). In the end, the A6 model won the top spot based on many statistical factors. Utilizing the temperature-based solar radiation model significantly increased the Abtew model estimation accuracy. It is strongly advised to estimate ET(0 )using the A6 model, which needs temperature as input data.