Evaluation of Water Use Efficiency and Prediction of Wheat Relative Yield with SWAP Model in Doroudzan Irrigation and Drainage Network

Water balance components are difficult to measure in short intervals because their measurement is time consuming and costly. Therefore, soil-water--plant models can be used for prediction of these components. In this study, to predict grain yield and evaluate water use efficiency, an agro-hydrological model, namely, SWAP was used. This study covered a 10-years period from 2000-2010. Based on the data measured in the field, the model was first calibrated for part of the Doroudzan irrigation and drainage network (under Ordibehesht canal downstream lands) for 2000-04, then, it was verified for the years 2005-09. The simulation results of the components of water balance estimated by SWAP and statistical comparison between the simulation results showed that the SWAP model was able to estimate yield accurately. The R2 for the predicted and actual crop production was obtained at 0.98 and, based on average t-test and at 95% level, they were not significantly different. Using the simulation results after validation, water productivity for irrigation water (WPI), transpiration (WPT), evapotranspiration (WPET), and for irrigation and rainfall (WPI+R) were 0.77-2.08, 1.15-2.10, 0.68-1.26, and 0.6-1.37 (kg m-3), respectively. Soil evaporation and using surface irrigation system caused reduction of WPET in comparison to WPI.