Comparison of Irrigation Scenarios in the Ebro Basin Using the SASER Modelling Chain

Water is a key resource for agricultural production and sustainable water resources management, particularly in Mediterranean regions where water availability is highly variable. Improving irrigation management is, therefore, essential to enhance water-use efficiency. In this context, land surface models provide a valuable tool to simulate irrigation practices and assess their impacts at regional scale. This study presents a comparison of irrigation scenarios simulated with the SASER modelling chain over the agricultural irrigated areas located within the Ebro basin (northeastern Spain). SASER is a physically based and distributed hydrological modelling chain that couples SAFRAN meteorological forcing with the SURFEX modelling platform, which includes an irrigation scheme. Drainage and runoff outputs are then provided to the RAPID scheme via the Eaudyssée platform to estimate streamflow. Three irrigation scenarios were defined: default, optimal, and realistic. The default scenario uses the standard irrigation parameters of the SURFEX irrigation scheme. The optimal and realistic scenarios share irrigation parameters derived from a farmer survey conducted in the Algerri-Balaguer region (eastern part of the Ebro basin). The main difference between both lies in the irrigation threshold: the optimal scenario considers the FAO-recommended threshold, while the realistic scenario is derived from in-situ data from the survey region, reflecting local conditions and more realistic irrigation behaviour. Overall, comparing the optimal and realistic scenarios, results show an average difference of about 20% in irrigation amounts, while differences in evaporation remain below 5%, and drainage differences range between 20% and 30%. Flood irrigation zones located along the Ebro riverbed and in the delta exhibit smaller differences between scenarios. In contrast, drip irrigation areas at the confluence of the Cinca and Segre rivers show the largest discrepancies. Overall, the study demonstrates how scenario-based modelling can support water management strategies and promote sustainable irrigation in the region.