Investigation of Evapotranspiration Changes of Autumn Irrigated Wheat in Iran under Climate Change Conditions

The purpose of this study was to investigate the changes in evapotranspiration of autumn irrigated wheat in Iran under climate changes conditions in order to carry out planning adapted to future climatic conditions and proper management of water productivity in the agricultural sector. Using the data of CCSM4 general circulation model and considering the length of growth period and plant growth coefficient of Irrigated wheat, the values of evapotranspiration in the base period 2005-2020 and the two future periods (2021-2060 and 2061-2100) under two scenarios of RCP4.5 and RCP8.5 were estimated, the relevant maps were prepared, and the spatial patterns of the phenomenon were investigated. The results showed that the evapotranspiration of irrigated wheat in Iran will increase by about 6% in the future period compared to the base period. It will be more in the distant future (2061-2100) than the near future (2021-2060) and in the RCP8.5 scenario more than the RCP4.5 scenario. The highest monthly values of evapotranspiration under RCP4.5 and RCP8.5 scenarios for May are 153 and 162 mm, respectively. Moreover, October and November, which are the first months of the growing season, will have the lowest increase in evapotranspiration in future, at approximately 14 mm. The amount of evapotranspiration of irrigated wheat during the growing period in the country varies from 330 to 971 mm in the base period to 340 to 1025 mm in the distant future under the RCP8.5 scenario. Increased evapotranspiration in the future will challenge many plans to supply water to the wheat crop in the country. Therefore, it is necessary to pay attention to water needs in the coming years, especially in April and May, which is the peak of plant activity and growth and the time of maximum water needs.