M.R. Goodarzi - Assistant Professor, Faculty of Civil Engineering, Yazd University, Iran
K. Janati - B.Sc. student of Civil Engineering, Faculty of Civil Engineering, Yazd University, Iran
A. Fatehifar - Ph.D. student of Water Resource Management, Faculty of Civil Engineering, Yazd University, Iran

Evapotranspiration after rainfall is the main component of the hydrological cycle that quantifies the amount of water lost. Since climate change directly affects the temperature and rainfall parameters, and the evapotranspiration rate is directly related to the air temperature, it is expected to have significant changes in the future. Therefore, in this research, the possible impacts of climate change on evapotranspiration changes under two RCP۲.۶ and RCP۸.۵ climate scenarios are investigated using statistical downscaling model (SDSM) and CanESM۲ atmospheric general circulation model output for the future period ۲۰۳۰-۲۰۵۹. Reference evapotranspiration rate was compared with Hargreaves-Samani and Thornthwaite methods in monthly and annual periods for the base and future periods. The results showed a mean increase of annual maximum and minimum temperatures in both scenarios from ۰.۰۶ to ۰.۲۶ °C compared to the base period. The highest increase was in May by ۲.۶۱ °C under the RCP۸.۵ emission scenario. Overall, the trend of evapotranspiration has been increasing throughout the years. The evapotranspiration in the Hargreaves-Samani method in the RCP۸.۵ scenario had the highest mean change of ۰.۰۸ mm or ۲.۷۹%. Although annual changes were not perceptible, as evapotranspiration in the basin reaches its maximum in July, the changes increased by ۰.۴۵ mm/day in RCP۸.۵ scenario. The results of monthly survey can be used in surface and underground water resources management and watershed projects estimating the water needs of plants plus appropriate timing of useful irrigation.

Evapotranspiration, Hargreaves–Samani, Thornthwaite, RCP, CanESM۲