Multiobjective optimization of daily scale irrigation schedules for rice in irrigation districts considering joint uncertainties in water supply and demand

Irrigation schedules are an important basis for allocating water resources and improving crop yields in agricultural production, and obtaining efficient and precise irrigation schedules to cope with changing environments is highly important for promoting the refined management of irrigation districts. Therefore, we adopted the Changgang Irrigation District (CID) in Heilongjiang Province as the study area, fully considered the joint uncertainty of water supply and demand, and constructed a three-dimensional (3D) copula-based multiobjective optimization model for efficient and precise regulation of rice irrigation schedules on a daily scale. Irrigation schedules for joint changes in runoff, precipitation and water demand were obtained, and the optimal irrigation mode to achieve synergistic enhancement of water conservation, efficiency and emission reduction was selected. The results revealed that the wetness-dryness asynchronous probability of CID runoff, precipitation and water demand was 3.98 times greater than the synchronous probability, which indicated that precise irrigation decision-making was needed to cope with the state of inconsistency under the condition of natural water inflow. The optimal irrigation mode at the daily scale outperformed the farmers' current irrigation schedules, with increases in irrigation water productivity, energy productivity and economic efficiency of 26.99%, 7.62% and 5.73%, respectively, and comprehensive water savings of 13.96% and 17.03%, respectively, at the field and irrigation district scales. The modeling framework improves precision irrigation decision-making considering complex interactions between known and unspecified water resource variables. This method is applicable to other irrigation districts and can provide decision support for comprehensively improving water security, food security and climate resilience in irrigation districts.