Assessment of anomalies and effects of climate change on reference evapotranspiration and water requirement in pistachio cultivation areas in Iran

Climate change is a major challenge for the agricultural sector. In this study, the effects of climate change on reference evapotranspiration and water requirement in pistachio cultivation areas in Iran were investigated. From observational data (1980–2018) as the baseline period and simulated data (2020–2080) under RCP, scenarios were used for the future period based on MarkSimGCM database. The results showed that in the baseline period, there were an increasing trend for annual air temperature and a decreasing trend for annual precipitation in pistachio cultivation areas in Iran. Reference evapotranspiration and water requirement will deviate in the future under the RCP8.5 and RCP4.5 scenarios from the baseline period. So, under RCP8.5 and RCP4.5, reference evapotranspiration will increase by 112 and 79 mm, respectively, compared with the baseline period. The highest water requirement in pistachio trees will occur in mid-growth stage (June–September), so that, under RCP8.5 and RCP4.5, the increase will be 114 and 82 mm, respectively, compared with the baseline period. From the spatial distribution, the highest amount of reference evapotranspiration and water requirement will occur in lowland and southern half of pistachio cultivation areas, especially in Kerman province. Increasing air temperature and consequently increasing reference evapotranspiration and increasing water requirement will be a danger alarm for water resources in the dry cultivation pistachio areas in Iran. According to projections, the shortage of water will intensify in the future, and as a result of climate change, many parts of the pistachio cultivation areas in Iran will be lost.