Comprehensive assessment of irrigation water requirements in Iran

A national web-based simulation portal was developed to estimate the irrigation water requirements at plain scale in Iran. The National Water Portal (NWP) consists of four national databases (climatic, soil, crop, and spatial data), a lumped water balance model, and a graphical user interface (GUI). The irrigation water requirements in standard conditions were estimated based on the dual crop coefficient approach presented by FAO 56. Net irrigation requirements (NIR) and gross irrigation requirements (GIR) were calculated for 125 different crops cultivated in the 609 plains in Iran. Results were aggregated at both political and hydrological scales. The statistical comparison between the estimated NIR and reported values in the literature reviews indicates a correlation coefficient of 75% with root mean square error (RMSE) of less than 280 m³ ha⁻¹. Results showed that sugar cane has the highest NIR value (18318 m³ ha⁻¹) among the studied crops, and sugar beet has the second highest NIR value (5100–11896 m³ ha⁻¹). The aggregated amount of NIR and GIR for the entire country was calculated as 47 and 105 billion cubic meters (BCM), respectively. Results indicate that 3.772 million cubic meter (MCM) of water can be saved by applying 15% water stress. By increasing the irrigation efficiency to 65% without considering any water stress, 3.482 MCM of water can be saved.