Perspective of spatio-temporal changes of evapotranspiration in Karun catchment basin during future periods and under greenhouse gases emission scenarios

In this study, the perspects of evapotranspiration changes in Karun catchment were investigated using Hargreaves- Samani method, LARS-WG6 downscaling model, and output of HadGEM2-ES model, under scenarios of RCPs for three periods of 2021-2040, 2041-2060 and 2061-2080 as compared to the period 1996-2015. The results show that the minimum average annual temperature in the catchment increases between 1.2 to 3.4 °C and the maximum temperature increases between 1.3 to 3.7 °C in future periods compared to the base period. The amount of evapotranspiration will increase in monthly, seasonal and annual time scales in the future climate, compared to the current conditions, so that the maximum increase in annual evapotranspiration in the distant future period and under the RCP8.5 scenario will be equal to 12.3% compared to the base period. The twenty-year box plot in future periods under different scenarios show that the highest evapotranspiration uncertainty occurs in the period 2061-2080 and under the scenarios RCP8.5 and RCP4.5 respectively. According to zoning maps of evapotranspiration changes in the basin, the highest amount of evapotranspiration changes will occur during the period 2061-2080 and under the RCP8.5 scenario in the western regions of the basin. Considering that Karun River originates from the mountainous areas on the north of the basin, increasing the temperature and in turn, increasing evapotranspiration in future periods will reduce the level of snow coverage in the area and will have significant negative effects on the flow of Karun River and can thus reduce the water resources of the basin.