Evaluation of agricultural water productivity for rice crop at the basin scale based on actual evapotranspiration in the Sefidrood basin

Evaluation of the agricultural water productivity is one of the essential indices to measure the efficiency and performance of management in irrigation systems that they have high agricultural water consumption and it is necessary to determine appropriate indices to conduct actual evaluation of this standard in a basin. In this regard, the use of actual evapotranspiration of agricultural products can be considered in calculating water productivity. To investigate this issue, the Sefidrood basin was selected as the study area and the actual evapotranspiration in addition of the irrigation water, was used to evaluate water productivity at the basin scale. For this evaluation, two indices were used: CPDIP (amount of product per unit of irrigation water and effective rainfall) and CPDET (amount of product per unit of actual evapotranspiration). The Comprehensive Water and Soil Assessment Model (SWAT) was used to estimate actual evapotranspiration and yield at the basin scale. For this purpose, at first the model was calibrated and validated using the SWAT-CUP tool according to the data of the hydrometric station at the basin level. The calculated R2 values for these two stages were between 0.61 to 0.75 and 0.51 to 0.72, respectively. Then the values of water productivity indices were calculated for the rice crop. According the results, the mean values of CPDIP and CPDET indices in the study period in the Sefidrood basin were 0.40 and 0.99 (kg /m3), respectively. As a result, the value of productivity index based on actual evapotranspiration is approximately 2.5 times of the value of index based on the irrigation water and effective rainfall. According to the findings in this study, CPDET is a suitable index to evaluate the agricultural water productivity at the basin scale; because it considers the repeated use of water percolation losses and surface water losses in the different sectors.