Adaptability evaluation for reference evapotranspiration (ET0) formulas in Guanzhong Region of Shaanxi

To investigate the adaptability of ET0 in in Guanzhong Region of Shaanxi, four ET0 equations including FAO-17 Modified Penman (FAO-MP), China scholar Modified Penman (PBX-MP), Penman-Monteith (PM) and Standard ASCE Penman-Monteith equation (ASCE-PM), were assessed . on the basis of measured data by weighting Lysimeters. The results showed that ASCE-PM was the best equation for estimating ET0 in semi-humid area with a linear regression coefficient of 1.03 (R2=0.87) and mean absolute error (MAE) of 0.31 mm, compared to the measured values. The next was PM equation, followed by the PBX-MP and FAO-MP equations. The deviation between calculated and measured values was mainly caused by radiation and aerodynamic terms. Air temperature, sunshine and relative humidity had a significant effect on radiation term, while wind speed had a significant effect on aerodynamic term. The ASCE Penman-Monteith equation was proved to compute the local ET0 properly in Guanzhong region of Shaanxi province.