Projected changes of potential evapotranspiration under RCP climate change scenarios (Case study: Bandar Anzali)

Accurate estimation of potential evapotranspiration is crucial in crop water use determination especially under climate change conditions. In this study, the changes of potential evapotranspiration values estimated using Hargreaves-Samani and Thornthwaite methods were investigated during the baseline period, 1986–2018. For future projection, the outputs of the general circulation model (CanESM2) under RCP2.6, RCP4.5 and RCP8.5 scenarios were downscaled using SDSM statistical model during near and far future periods (2025-2050 and 2075-2100). The simulation results showed a rise in temperature in future periods and all scenarios. The results showed that ETp will increase from 2025 to 2100 under three scenarios, except for the Thornthwaite method estimations in March. In the RCP2.6 scenario, the highest increase in ETp in the Thornthwaite method was obtained in July, equal to 55 mm. This value was calculated in the Hargreaves-Samani method equal to 1.63 mm in April. In the RCP4.5 scenario and near future period, the projected rise in ETp values by Thornthwaite method in month of July is 54.96 mm and Hargreaves-Samani method for month of January was 1.45 mm. These values for the same month and methods, in case of RCP8.5 scenario, were 40.34 and 1.72 mm, respectively. According to the results, the lowest increase in ETp will occur in the RCP4.5 scenario between years 2025 and 2050 and in the RCP8.5 scenario between years 2075 and 2100.