Optimizing oilseed flax yield and stability under climate variability in North China

Oilseed flax production in the rainfed regions of North China suffers from high climate‑induced yield instability (coefficient of variation, CV = 24%–54%), which threatens farm income. Although adjusting sowing date and cultivar are recognized adaptation strategies, their integrated effect on long‑term yield stability has not been quantified. Here, we aimed to identify optimal sowing‑date–cultivar‑maturity combinations that enhance both productivity and stability. Using the process‑based SIMPLE model calibrated with local field data (yield performance: d‑Index = 0.94, RRMSE < 10%), we simulated rainfed flax growth from 1961 to 2020 at six representative sites. Different maturity groups, defined by their thermal‑time requirements, were evaluated across sowing dates ranging from early March to late June. A high‑stability index (HSI; calculated as (mean yield - yield standard deviation) / overall mean yield) was used to identify the optimal management practice. Mean yield in eastern sites was 110% higher than in western sites (2367 vs. 1128 kg ha⁻¹, p < 0.05). Late‑maturing cultivars had 94% higher yield than medium‑maturing cultivars (p < 0.05). The optimal sowing window was from May 10 to June 9 (HSI > 0.7), which improved the HSI by 0.15 compared with late‑April sowing. Over the study period, the optimal sowing window delayed by 7 days in Urumqi and advanced by 8 days in Chifeng. We conclude that delaying sowing to synchronize the water‑sensitive flowering stage with the period of highest rainfall probability, combined with the use of late‑maturing cultivars, can effectively enhance system resilience. This study provides quantitative, site‑specific management strategies for climate‑adaptive flax production in semi‑arid regions. • SIMPLE model accurately simulated flax ( d -Index=0.94, RRMSE<10%). • Optimizing sowing and cultivar raised HSI by 0.15 and yield up to 110% (region) / 94% (cultivar). • Best practice: late cultivars sown between May 10 and June 9. • Optimal sowing dates shifted ( +7 days in Urumqi, −8 in Chifeng) over 60 years. • Study provides site-specific strategies for climate-resilient flax farming.