Modeling the effects of irrigation management scenarios on winter wheat yield and water use indicators in response to climate variations and water delivery systems

Agriculture is the major user of the available fresh water resources at the global scale. However, water resources are negatively affected by climate change. Therefore, agricultural water management is globally considered as a key solution to address the current and future water resources challenges. In this study, a large number of recommended and probable scenarios of different deficit irrigations, climatic conditions and rainfall patterns, and sowing dates were defined and modeled under Rotational and On-demand irrigation scheduling (IS). For this purpose, the AquaCrop model that was calibrated and validated based on the observed data of 15 growing seasons was applied on winter wheat in a warm and semi-arid environment in the south-west of Iran. The AquaCrop model simulated grain yield accurately with normalized root mean square error (NRMSE) of 5% and 6% for calibration and validation, respectively. Analyses showed that the yield response factor in the different scenarios was higher than 1 in all climatic conditions that indicates high wheat sensitivity to water stress in the study area. Besides, analyzing the optimal irrigation plans for all possible climatic conditions and deficit irrigation levels showed that irrigation at the stem elongation stage was the most critical irrigation event. Further analysis also showed that November 8th - 22nd is the optimal window for achieving the highest grain yield in all climate conditions. Modeling showed that the Rotational IS is more adaptable to deficit irrigation practices due to maintaining higher grain yield and water productivity compared with the On-demand IS. Indeed, it is possible to maintain grain yield and increase water productivity by applying deficit irrigation up to 40% of full irrigation under Rotational IS. In conclusion, the results of this scenario-based modeling study showed that achieving the highest grain yield and water productivity in a large irrigation area depends on a combination of deficit irrigation scenarios and the water delivery systems in response to climatic variations. However, changing the water delivery systems from Rotational to On-demand requires expensive infrastructure investment and irrigation scenarios analysis before any decision.