Modeling the Impact of Climate Change on Onion (Allium cepa) Yield and Economic Production: A Multi-Model Approach

Although machine learning models for onions (Allium cepa) have recently emerged, process-based models are required to capture physiological responses under climate volatility. This study addresses this need by integrating the Agricultural Policy/Environmental Extender (APEX) crop growth model with an econometric framework to simulate onion yields and economic returns under shifting climate regimes. The APEX-onion model was calibrated for onions’ cold-weather dynamics and bolting partitioning, achieving robust multi-site regional validation (PBIAS = 2.48%, RMSE = 1.39 Mg ha−1). Decadal projections (2026–2035) across four CMIP6 models under the SSP245 and SSP585 pathways reveal that warmer conditions and elevated CO2 generally enhance yields (by 9–22%), whereas compound radiation and rainfall anomalies trigger severe water stress (>110 days) and yield penalties. An economic harvest ratio (EHR) model demonstrated that 100% unbolted harvests do not monotonically maximize farm profit due to wholesale price collapses under price-inelastic vegetable demand. Moderating marketable volumes (allowing an effective supply buffer averaging 39.0–42.6% and up to 46.5% during bumper years) protects farm revenue, whereas full marketable yields are essential during climate-driven shortages. This integrated framework provides actionable economic thresholds for agricultural climate adaptation.