Sensitivity analysis of various reference evapotranspiration (ETo) models with FAO 56 Penman Monteith for semi-arid region of India

Abstract

Daily crop ET of Triticum austivum L. and Cajanus cajan L. was monitored with gravimetric lysimeter during 1995-1997 at Rahuri, India (long. 780 18’ E and lat.190 45’ N) and was compared with various ETo models by statistical indicators like RMSE, MBE, t-statistic for adoption in semi-arid region of India. The crop evapotranspiration, on an average of three years was 1068.2 mm during crop growing season however, the reference evapotranspiation (ETo) in case of Hargreaves model was 1864.3 mm, the open pan 1636.6 mm, radiation balance 2335.0 mm, FAO56 Penman Monteith 1597.5 mm, Blaney Criddle 2021.5 mm and Modified Penman 2508.3 mm. The FAO56- PM model had lowest RMSE (2.89 mm day-1 ) and MBE (1.05 mm day-1 ) followed by Hargreaves (RMSE 3.28 mm day-1 ). The seasonal crop ET was 537.9 mm in red gram and 418.1 mm in wheat. The regression analysis between crop coefficient (Kc) and ETo models were agreeable in Hargreaves and Modified Penman model as evidenced by higher R2 values. Similarly regression analysis between crop coefficient and cumulative GDD had significant response with R2 of 0.57 to 0.83 in wheat and R2 0.31 to 0.59 in red gram. The regression analysis between SDD and crop coefficient had R2 0. 94 in red gram and 0.90 in wheat