Comparison the accuracy of predicted maize evapotranspiration using real time meteorological data and conventional methods in Karaj climate

Accurate estimation of crop evapotranspiration has a major role in optimum agricultural water management. The aim of this study was to evaluate the accuracy of using real time (3days in-advance forecasts) temperature data for estimation of maize evapotranspiration comparing to conventional methods in Karaj, Iran. To achieve this goal, the crop evapotranspiration (ETc) was calculated using FAO ETo Calculator software. Two climatic data set were deployed for comparisons i.e. 10 years (2004-2014) mean values of meteorological data of maize growing season and real-time 3-days forecast of temperature. Actual values of evapotranspiration based on a water balance approach were measured using watermark sensors during the summer 2014 as a control treatment. Comparison of ETc measurements with estimations obtained by using different climatic data and also a combined set of data (real time and long term means) revealed that estimated values of ETc using combined weather dataset for amount of 551.6 mm/season and ETc values estimated using 3 days forecasts of air temperature (497.2 mm) had maximum (12%) and minimum (2%) difference with actual ETc values obtained by water balance method i.e.565.64 mm, respectively. Both proposed methods showed underestimation. Further studies are recommended for more scrutiny.