The study aimed to analyze the impact of climate change on water requirements and productivity of improved Arabic wheat in the Sana'a Basin, by conducting field experiments for two agricultural seasons (2023-2024 AD) on the farm of the Faculty of Agriculture, Sana'a University. It included three irrigation treatments: (full irrigation (I1), 75% deficit irrigation (I2), and 50% deficit irrigation (I3) of the full irrigation) using a randomized complete block design. The Aqua Crop model was used for modeling, calibrated with data from the first agricultural season of 2023 and validated with data from the second agricultural season of 2024. The model was validated using three global climate models: CNRM-CM5, GFDL-ESM2M, and EARTH-EC, and two gas emission scenarios: Rcp4.5 and Rcp8.5, for each model, and at an increased and constant CO2 concentration (350 ppm). The study revealed that irrigation treatment (I2) achieved the highest water productivity (WPET) values during the two seasons, ranging from 0.72 to 0.69 tons/m³, respectively. Its water permeability (WPI) ranged from 0.74 to 0.72 tons/m³, respectively. The correlation coefficient (R²) showed high agreement between the calculated and predicted values for grain productivity and biomass for the two seasons, ranging from 99.93 to 100. and (99, 95%) (%), respectively. The grain productivity values for the two seasons were higher in irrigation treatment (I1), ranging between (2.27, 2.52) (tons/ha), respectively, compared to irrigation treatments (I2) and (I3), which ranged between (2.15, 1.95), (1.0, 1.02) (tons/ha), respectively, at a significance level of (0.05). Climate changes recorded an increase in maximum temperatures by 2.47°C for the RCP8.5 scenario and the period 2040–2059, according to the EC-Earth model. Meanwhile, rainfall recorded a decrease of 16.18 mm in the RCP8.5 scenario for the same period and the GFDL-ESM2M model, compared to the reference (historical) period (2005 , 1986) With increased CO₂, irrigation treatment (I1) achieved the highest grain productivity value. (3.24) (tons/ha) according to the RCP8.5 scenario for the period (2020-2039), while under constant CO₂, the lowest value was recorded for irrigation treatment (I3) (0.82) (tons/ha) according to the RCP4.5 scenario for the same period . The highest actual evapotranspiration values were recorded for treatment (I1) at (384.60) (mm) according to the RCP8.5 scenario for the period (2020-2039) under constant CO₂. The lowest values were recorded for treatment (I3) under increasing CO₂, at (266.0 (mm) according to the RCP8.5 scenario for the period (2039-2020 ) The study showed that the experimental site will witness an increase in the productivity of the improved Arabic wheat crop, and assuming an increase in carbon dioxide concentration, this contributes to increased crop productivity.
