Simulation of Water Productivity Indices Using SWAP Agrohydrological Model and Comparison with Field Conditions in Paddy Soil

In recent decades, several models have been developed to simulate farm water management. The main focus of most researchers is obtaining more products per unit of water consumed. Water productivity defined as crop yield per unit of water consumption. Due to limitation of water resources and its optimal consumption in order to save water and increase its productivity, this study was conducted to simulate water productivity indices of rice (Hashemi caltiver) using SWAP model in paddy soils at field scale. For this purpose, two closed-ended lysimeters were used to measure the actual evapotranspiration. The quantity of evapotranspiration was measured daily and water productivity based on irrigation water (WPir) and evapotranspiration (WPET) was calculated and compared with the simulated values afterward. The obtained results indicated that the SWAP model had a high accuracy for estimating amount of yield (R2=0.90 and RMSE=648.73) and the amount of water consumed in the evapotranspiration process (R2=0.89 and RMSE=164.07). Using the calibrated SWAP model, the water productivity indices from division of yield on evapotranspiration (WPET) and yield on irrigation water (WPir) in the studied farm was estimated amount of 0.553 and 0.876 kg/m3, respectively. Also, results showed that with increasing irrigation efficiency, elimination of deep percolation and reduction of evaporation, water use efficiency increases by 30%. In general, for optimal management of paddy soils in field scale and considering the optimal yield at harvest time, serious attention must be paid to water efficiency to come up with most effective ways to deal with water crisis and to increase the quantity and quality of rice production.