Regulation of efficient water use in paddy fields via the simulation of the water cycle in cold regions under random precipitation conditions

The unique freeze‒thaw cycle in cold regions complicates irrigation. Field monitoring and experiments simulated the water cycle during thawing and growing periods, analyzing hydraulic connections. This led to coupling a hydrological balance model, the Environmental Policy Integrated Climate (EPIC) model, and a carbon emission model into a multi-objective optimization framework for rice irrigation, aiming to enhance production, save water, and reduce emissions. Using Monte Carlo simulation and the Non-dominated Sorting Genetic Algorithm III (NSGA-III), dynamic water distribution plans were developed considering precipitation variability. Modeling the 0–60 cm soil layer as continuous improved soil moisture simulation, resulted in soaking irrigation with 16 %–21.8 % water savings. Optimized irrigation increased maximum yield by 1.6 %–4.7 %, reduced carbon emissions per unit yield by 16.4 %–18.6 %, and saved 7.7 %–9.5 % water compared to conventional methods. Key allocation periods are tillering and jointing-booting initiation, optimizing distributions for 57 %–72 % of the growth period, supporting sustainable water management in cold-region rice paddies.