Evaluation perspective of the Aras Basin reference crop evapotranspiration in future climatic condition under RCPs scenarios

In this study, the perspective of reference crop evapotranspiration (ETo) in the southern part of the Aras River Basin under climate change condition was drawn using SDSM downscaling. For this purpose, meteorological data of selected synoptic stations located in this basin were used and after receiving the downscaling outputs for the parameters required for estimating ETo by Penman-Monteith FAO-56, basin ETo was calculated for the near future (2021-2050). In this regard, daily reanalysis NCEP data and station daily data include: maximum and minimum temperature, wind speed, relative humidity and sunshine hours as well as output data on CanESM2 model under RCPs scenarios were used to generate future station data for estimate Aras Basin ETo. The studied stations included: Ahar, Ardabil, Parsabad, Jolfa, Khoy and Makoo and the base period for the data was considered 1985-2005. First, the efficiency of SDSM in simulating the parameters required for ETo estimation was evaluated by comparing NCEP simulated data with station data. Their comparison indicated the appropriate performance of the model in simulating data. Therefore, climatic parameters were simulated using the CanESM2 model under RCPs scenarios for the future. After calculating their monthly values, in CROPWAT was entered to estimate the basin ETo and trend of the variable for the next three decades were calculated. The results showed that the basin ETo in the future period compared to the base period will increase by an average of about 7 mm per year. In terms of stations, there will be an increase in Parsabad (102 mm) and Jolfa (66 mm). This increase also means an increase in the water needs of plants. Also, the future trends of ETo in Khoy, Makoo, Ahar and Ardabil will be decreasing.