Yield-loss effects of compound cold and overcast hazards on rice during booting and flowering stages in high-latitude China

Compound cold and overcast hazards during the booting–flowering stages of rice in high-latitude regions of China resulted in yield loss. However, its quantitative assessments remain limited and systematic analyses of the underlying mechanisms are still lacking.
Our study characterized the spatiotemporal patterns of individual and compound occurrences of cold and overcast events during the booting–flowering stages of rice in the study region, and then employed the validated rice ecophysiological model ORYZA (v3) to simulate yield responses under constructed scenarios of low temperature, low radiation, and compound events. Partial least squares path modeling (PLS-PM) was used to elucidate the mechanisms by which temperature and radiation under compound hazards conditions affect rice yield variation.
Over the past four decades, the occurrence proportion of cold events (CE) decreased significantly at 11.2 pp 10yr⁻¹, whereas overcast events (OE) and compound cold and overcast events (COE) increased by 5.3 and 0.9 pp 10yr⁻¹, respectively. COE hotspots were located in the Sanjiang Plain, reaching a maximum frequency of 41.0%. ORYZA (v3) demonstrated good applicability in simulating yield reductions under CE, OE, and COE, showing good performance with RMSE and NRMSE of 2.0–4.2 percentage points and 16.0%–19.3%, respectively. During booting, yield losses under compound hazards (1.1%–28.2%) exceeded those under low temperature alone (0.5%–21.3%) or low radiation alone (0.8%–9.7%); the specific indirect effect of the “temperature–panicle–yield” pathway reached 0.84 (vs. 0.77 under strong single cold), indicating amplified sink limitation centered on panicle development. During flowering, compound-hazard yield losses (2.8%–23.5%) were comparable to overcast alone (3.6%–23.4%), and both exceeded cold hazards (1.5%–7.7%). Low radiation dominated, with the “radiation–panicle–yield” pathway (0.64) stronger than the temperature pathway (0.56), and an additional indirect yield penalty (+0.10) via increased stem allocation (FST). Overall, booting-stage losses were governed mainly by low-temperature-driven sink limitation, whereas overcast-induced constraints on source capacity primarily controlled flowering-stage losses.