Extended Abstract

Introduction: Historically, global producers have chosen maize, wheat, and rice as the main crops for their remarkable adaptability in different regions and climates, their wide acceptance and consumption by the population, and their nutritional status (FAO, 1995). Together, these three products provide 60% of global food energy consumption (FAO, 1995) because more than half of the world's population uses them as their main food (FAO, 2021; Haile et al., 2017). The process of climate change has been raised as a major challenge of the 21st century, which has great effects on the agricultural sector, water resources, the environment, and ultimately food security. Meanwhile, wheat is considered the most important rainfed crop in arid and semi-arid regions of the world, especially in Iran. The phenological stages and yield of rainfed wheat will shift in response to climate change. According to a study of research, changes in the climate would also affect agricultural and climatic processes, resulting in changes to yield, phenological periods, and climatic variables (Helali et al., 2022). The goal of this study was to examine how the climate and agricultural factors have changed over time using the AquaCrop and CMIP6 models in the context of the SSP scenario in the western Iranian province of Hamedan.

Materials and methods: The study area is Hamedan province, located in the west of Iran, which mainly has a semi-arid climate. This province is considered one of the leading provinces in the production of rainfed wheat, so that the average yield of wheat in the studied locations fluctuates, which is mainly due to changes in climatic variables, droughts, cultivated varieties, and management strategies. In this study, the data of Hamedan, Malayer, Nahavand and Nowhzheh stations were used. The climatic data included minimum and maximum temperature, precipitation, relative humidity and wind speed on a daily scale. In this research, the fluctuation of climatic and agroclimatical variables in different stages of rainfed wheat phenology was investigated using the CMIP6 climate model under the SSP scenario and the AquaCrop model. Then the values of evapotranspiration, heat demand and length of phenological period were calculated for rainfed wheat variety Azar 2, which is the dominant variety of the studied area. The phenological periods included germination, vegetative, flowering and ripening periods and the entire growth period. The Socio-Economic Pathway (SSP) scenarios for the years 2021–2050 and the base period from 1990 to 2014 were used. Additionally, the AquaCrop model was used to compute the modeling of phenological stages, evapotranspiration, and heat demands (growing degree days). Based on the crop year, six planting dates were taken into consideration, starting on September 22 and spaced out by ten days.

Results and discussion: When rainfall, maximum temperature, minimum temperature, relative humidity, and wind speed were simulated using various CMIP6 models, it was shown that the BCC-ESM2-MR, MRI-ESM2-0, and Can-ESM5 models performed better than the other models. While other climate variables, particularly in the SSP5-8.5 scenario, have had incremental changes compared to the base period, the projection results using the best model in the base period showed that the amount of precipitation in the future period will decrease under all scenarios in all stations, with the largest decrease occurring in the SSP5-8.5 scenario. The summary of the obtained results shows that the amounts of precipitation, evapotranspiration, thermal demand, and the length of the phenological period will increase or decrease with the change of the cultivation date, which shows that the change of the cultivation date can be used as a solution to adapt to climate change. The results showed that in the future climate, under CMIP6 models and SSP scenarios, precipitation amounts will decrease, while the variables of growing degree day, evapotranspiration, and relative humidity will experience incremental changes depending on the phenological stage. Meanwhile, the variable length of phenological periods will experience both decreasing and increasing trends. Based on these findings, it is anticipated that climate effects on the various phenological stages of rainfed wheat in Hamedan province would intensify in the future. In light of these changes, it is imperative to investigate the impact of climate on rainfed wheat production. It is recommended that the researchers use a variety of agricultural models and other management techniques to investigate the impact of these occurrences on the yield of rainfed wheat.