LAUSR

Abstract Experimental methods of reference evapotranspiration (ET0) calculation require extensive environmental data, not readily attainable everywhere. Therefore, two multivariate models using Levenberg–Marquardt nonlinear least-squares algorithm were developed in this research to estimate daily ET0 by focusing on fewer meteorological variable inputs. Different meteorological parameters were measured for two consecutive years in outdoor and greenhouse environments. The ET0 models were developed for the aforementioned environments in terms of three major parameters, namely air temperature, relative humidity and pan evaporation. To construct the ET0 models, three steps were carried out, (i) outdoor wind speed was estimated in terms of the major parameters with appropriate accuracy (R 2 = 0 . 42 , AR 2 = 0 . 4 and RMSE = 0.176 m/s), (ii) net radiation was estimated in terms of the major parameters and estimated wind speed with high accuracy (their R2 and AR2 > 0.47 and RMSE