Calculation of Net Irrigation Requirement of Agricultural Products in Qaleh Chay Catchment and Its Evaluation with the Data of National Water Document

The main purpose of this study was to calculate the net irrigation requirement of agricultural products in the Qaleh Chay catchment in the current climatic conditions and evaluate it with the data of the National Water Document (NETWAT). For this purpose, the reference evapotranspiration was calculated by the Penman-Monteith-FAO method for the years 2013 to 2019. Subsequently, the plant coefficients were modified according to the guidelines of FAO 56. Then the effective rainfall and net irrigation requirement were calculated. Finally, the net irrigation requirements of the region were compared with the data of the National Water Document. The results showed that the values obtained in this research were in all cases higher than the values mentioned in the National Water Document. This difference was due to the fact that the information used for the calculations in this study was from the year of establishment of the meteorological station of the catchment (2012), while the calculations in the national water document were related to meteorological stations in neighboring cities and years before 1378. Also, increasing temperature and decreasing rainfall in recent years have increased the irrigation requirement compared to previous years. Finally, it is suggested that the estimation of irrigation requirements be done according to meteorological data of recent years to be closer to reality.