Modeling the impact of water deficit on wheat yield under climate change conditions

Abstract
Background and objectives: The plant have a close relationship with the climatic conditions and their surrounding environment to go through the stages of growth and development. Therefore, the knowledge and understanding of the effect of atmospheric parameters on plant yield and production efficiency is very important.
Materials and method: The experiment was conducted in the form of a randomized complete block design in three replications with five experimental treatments including: no water deficit (control) (NWD), water deficit at the booting stage (WDB), flowering (WDF), milking (WDM), and doughing (WDD), in Varamin, Iran. Simulating the future climate, using the HadGEM general circulation model under the RCP4.5 and RCP8.5 climate scenarios in the three periods of 2025, 2055 and 2085, by the AgMIP model using long-term climate data related to the base period (1980-2009) was done. SSM-Wheat model was used to simulate wheat growth.
Result: Based on the findings, the changes of maximum and minimum temperature compared to the baseline in the periods of 2025, 2055 and 2085 showed that the maximum and minimum temperature under RCP8.5 scenario increased more than RCP4.5. So that under the RCP8.5 scenarios, the maximum temperature increased by 2.1, 4.3, and 6.9 (ºC), respectively. and the minimum temperature increased by 1.5, 3.2, and 5.6 (ºC) respectively. The amount of precipitation in the periods of 2025 and 2055 under the RCP8.5 scenario increased by 4.9 and 5.9%, respectively. While the amount of precipitation in the period of 2085 under RCP8.5 scenario showed a decrease of 12.6%. The results showed that both in the no water deficit and the water deficit at the flowering stage in the periods of 2025, 2055 and 2085 under RCP4.5 and RCP8.5, the FASW by passing through The early stages of wheat cv. Mehregan growth were faced with water shortage stress and the need for irrigation was necessary from that time. Also, the length of the growth period of wheat cv. Mehregan in 2085 period was shorter compared to 2055 and 2025 periods, and this period reduction was much more intense than the growth season. The evaluation of grain yield in 2085 under the RCP8.5 scenario showed that the water deficit at the flowering stage significantly reduced grain yield by 16.8%.
Conclusion: In the climate change conditions, the maximum and minimum temperatures under RCP4.5 and RCP8.5 scenarios increased during the studied periods compared to the base period. This increase was more intense from 2025 to 2085 and also under the RCP8.5 scenarios. Based on the findings, the FASW in the no water deficit and the water deficit at the flowering stage at the 2025, 2055 and 2085 periods under both scenarios showed the absence of water stress. The results of the evaluation of the grain yield showed that the reduction of grain yield under the RCP8.5 scenarios was more obvious and more severe than the RCP4.5 scenarios. The water deficit both the booting and especially flowering stages caused a significant decrease in grain yield.