Abstract: Rice production, essential for global food security, is increasingly impacted by climate variability and genetic improvements. However, limited research has systematically quantified the individual contributions of climate change and genetic advancements to rice yield trends, particularly in high-latitude regions such as Harbin city, Heilongjiang Province, China. This study addresses this gap by using the AquaCrop model to partition the effects of climate change and genetic enhancements on rice yields over recent decades. The objectives were to evaluate the relative influences of climate and genotype on yield trends, assess irrigation efficiency under continuous flooding (CF) and alternate wetting and drying (AWD), and identify optimal transplanting dates for yield and water productivity. Four years of paddy field data were used to calibrate and validate AquaCrop for three rice varieties (V₁, V₂, and V₃) under CF and AWD irrigation. Historical climate data were sourced for simulations. Key findings indicate that climate change accounts for 60%‒70% of yield improvements, while genotype contribute 30%‒40%. AWD achieved grain yields within 1% of CF, while improving water productivity by up to 7% in later (V₂ and V₃) varieties and delayed transplanting dates. Additionally, 15 May was identified as the optimal transplanting date, yielding up to 7.53 t/hm² under CF with biomass reaching 18.35 t/hm². These findings highlight strategies for sustainable rice production in water-scarce regions and emphasize the role of genotype development in climate adaptation.

Key words: flooding, wetting and drying, rice, biomass, transplanting, cold region, yield