Analyzing the Gap between Irrigation Water Requirement and Supply at the District Scale

Agriculture is the world's largest consumer of freshwater and it is now well established that freshwater availability is decreasing in many parts of the world (particularly in the Mediterranean region) as a direct result of global climate change. Therefore reducing the gap between the effective irrigation water requirements and the water supplies to irrigated areas is a key challenge to support the adaptation of agricultural systems to future climate and water scarcity conditions. In this work, an agro-hydrological model was used to assess this gap in seven pressurized irrigation districts (ranging from about 200 to 3000 ha in size) located in the Padana plain (i.e. the largest irrigated region in the EU). Specifically, daily irrigation water requirements estimated by the IdrAgra model (https://idragra.unimi.it/resources/) were compared with the observed water supplies at the head of each district for the period 2016-2022 including wet, medium and dry rainy seasons. Detailed land use and soil information, irrigation efficiency maps, agro-meterological and remote sensing data have been integrated into the model to provide highly accurate irrigation water requirement estimates. The results show that a mismatch between water supplies and actual irrigation water requirements occurs quite often, with water supplies often exceeding crop water requirements in the wet seasons and falling short in the dry seasons. Part of this mismatch is due to the rigidity of water management criteria (e.g., fixed irrigation scheduling between plots within the district, lack of rapid adaptation of water supply to irrigation demand), which makes it difficult to align water distribution with real irrigation needs. The analysis of these results has shown that there is a margin for reducing the gap between supply and demand in the seven study districts through the improvement of irrigation management practices that we believe could be applied elsewhere in similar irrigation contexts.