Evaluation of Valiantzas ET0 Equations against FAO56-PM Model in Indian Semi-arid Climatic Conditions

In this study, performance of three forms of Valiantzas ET0 equations namely, (i) requiring full meteorological dataset, (ii) not requiring wind speed data, and (iii) not requiring both wind speed & relative humidity data for Indian semi-arid Hissar and Parbhani districts in comparison to widely accepted FAO-56 PM model was evaluated in terms of different statistical indices and their ranking based on GPI values. All Valiantzas ET0 equations requiring full meteorological dataset under-estimated FAO56-PM estimates in the range of 9.10 to 21.84% at Hissar while they over-estimated it in the range of 0.98 to 8.32% at Parbhani district. Valiantzas equations not requiring wind speed data under-estimated FAO56-PM ET0 values in the range of 3.90 to 34.56% at Hissar and over-estimated the same in the range of 11.55 to 41.28% at Parbhani. The Valiantzas equations not requiring both wind speed & relative humidity data under-estimated FAO56-PM ET0 estimates in the range of 23.80 to 57.56% at Hissar and over-estimated it in the range of -1.80 to 6.96% at Parbhani district. Among all 16 considered Valiantzas ET0 equations, Val 7 and Val 2 (equations requiring full meteorological dataset) showed best performance at Hissar and Parbhani districts, respectively while Val 16 (equation not requiring both wind speed & relative humidity data) and Val 9 (representing Valiantzas equations not requiring wind speed data) were adjudged worst at Indian semi-arid Hissar and Parbhani districts, respectively.