Phenological Response of Winter Wheat to Climate Change in Huang-Huai-Hai Plain

A comprehensive analysis is conducted on the spatiotemporal response of winter wheat phenology to ongoing climate change in Huang-Huai-Hai Plain, a vital grain production base in China. Utilizing long-term, high-quality observations from 62 nationally managed agrometeorological stations spanning the period of 1981-2024, the shifts in key phenological stages and corresponding growth phase lengths are systematically quantified. The integrated analysis employs a suite of methods, including kernel density estimation, linear trend analysis, and structural equation modeling (SEM), to disentangle the complex drivers behind these temporal changes and spatial patterns.Results reveal a pronounced and coherent spatiotemporal pattern characterized by delayed early vegetative stages but advanced later reproductive stages, resulting in an overall shortening of the growth cycle. Specifically, a general trend of delay is observed for the dates of sowing, emergence, tillering, and the onset of overwintering. Following a spatially heterogeneous regreening stage, the rising stage and all subsequent reproductive stages are significantly advanced, with anthesis showing the most rapid advance at a median rate of -2.23 d·(10 a)^-1. This phenological restructuring leads to a significant compression of the entire growth period, which shortens at a rate of -2.86 d·(10 a)^-1 at 91.94% of the stations. However, changes in the durations of specific growth phases are markedly asymmetric. The critical phase from overwintering onset to rising shortens sharply at a rate of -1.96 d·(10 a)^-1. Conversely, the grain filling phase is lengthened by 1.23 d·(10 a)^-1 at 83.87% of stations. Spatially, these trends exhibit significant latitudinal differentiation. The delay in overwintering onset intensified from north to south, while the advancement of post-regreening stages is most pronounced in southern low-latitude zones. The shortening of the overwintering-to-rising phase is particularly severe in the central latitudinal belt. To unravel the underlying mechanisms, a structural equation model is constructed. The model quantified a dual-squeeze mechanism: Climate factors directly compress the total growth period, and also indirectly compress it by advancing phenology, which interacts with the shortening of key intermediate phases. These pathways together explain 79% of the variance in growth period length. Geographical factors, especially latitude, are confirmed as the fundamental determinant of the baseline spatial pattern, upon which climate change signals are superimposed.This research contributes to a deeper mechanistic understanding of "climate-crop-management" interactions, providing critical evidence for optimizing regional cropping systems, calibrating crop models, and formulating targeted adaptation strategies to safeguard production. Future studies should further disentangle the contributions of genetic improvement and management adaptations from pure climate effects and investigate the links to final yield outcomes.