AquaCrop model is an important tool for predicting and evaluating the impacts of environment and irrigation water management on crop productivity. The current study aims to evaluate AquaCrop model for wheat yield during years of guaranteed rain in Rabi'a rejoin and to study the effect of rain distribution on productivity. with an attempt to suggest the best date for supplemental irrigation during the season to obtain the best productivity of wheat and irrigation water. AquaCrop model was calibrated with climatic and field data for Rabi'a region and start date of agricultural season was determined based on date and amount of valuable rain, with initial soil water content calculated for a root depth equivalent to 30 cm.
The effect of rain distribution before sowing on productivity for different sowing dates (November 1, November 15, December 1, December 15, and January 1) was also studied. As well as determining the extent of need to add irrigation before sowing to improve productivity, in addition to determining the best date and depth of supplemental irrigation according to water need during wheat growth stages. . The results showed the importance of studying and observing the rain distribution before sowing and during the growing season, as delaying the sowing date can lead to an increase in productivity, as adding water with a depth of 20 mm was considered useful for improving productivity due to poor rain distribution. There was also a marked increase in productivity when adding supplementary irrigation of (60-70) mm during third or fourth stage of growth and according to the rain distribution for each year.