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

Abstract

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.