Spatial Changes of Seasonal Reference Evapotranspiration in Iran Based on CMIP6 Models

The aim of the present study is to investigate the spatial changes of seasonal ETo in Iran in the future (2020–2050), based on SSP1-2.6, SSP2-4.5 and SSP5-8.5 scenarios of CMIP6 models (MRI-ESM2 and GFDL-ESM4) compared to the observed data (1992–2014). The FAO56-PM method was used to estimate ETo, and the CV was utilized to investigate the changes. The results showed that ETO will decrease in all seasons across the country under all GFDL-ESM4 scenarios (except winter under SSP5-8.5). However based on the scenarios of the MRI-ESM2 model for 2020–2050, the amount of ETO will increase in the southeastern and southern regions in winter, but in the northwest, west, east, and areas corresponding to the Zagros highlands, ETo will decrease. In spring and summer, ETo will increase in the Caspian Coast, northeastern, western and interior areas of Iran, and even in the northwest (in summer). In the fall, ETO will increase in the eastern and western regions of the country, east of the Caspian Sea and the northern Iranian plateau. Fall, summer, winter and spring, respectively, represent the highest levels of spatial changes in ETo, but it will expand only according to the MRI-ESM2 model in the winter (21% – 25%) under SSP1-2.6. Other seasons show fewer changes than in the past, based on models. Accordingly, the need for detailed planning in water resource management is emphasized, especially in the southern and eastern parts of Iran toward the inner areas.