Phenophase-specific responses of winter wheat to drought stress: insights from four decades of observations in Shandong, China.

As a cornerstone of global food security, winter wheat (Triticum aestivum L.) exhibits yield dynamics that are critically dependent on water availability during pivotal phenological stages. Leveraging monthly meteorological data (1980-2022) and ground-based phenological records from Shandong Province, China, this study quantifies drought conditions during essential growth phases using the seasonal-scale Standardized Precipitation Evapotranspiration Index (SPEI-3). By integrating the Theory of Runs with correlation analysis, we characterize the spatiotemporal patterns of drought and assess phenophase-specific responses over the past four decades. Our findings reveal that: (1) Drought intensity during key phenological stages generally weakened from 1980 to 2022, indicating a long-term alleviation of drought stress. Spatially, droughts were more severe and persistent in western and northern regions, relative to shorter, less frequent, and milder events in the south and east. (2) Phenological shifts displayed a clear divergence: the emergence and tillering stages of winter wheat were delayed, whereas the jointing, booting, and maturity stages advanced across most stations. (3) Drought sensitivity varied considerably across developmental phases. Booting, jointing, and maturity exhibited the strongest negative correlations with drought severity (as indicated by SPEI-3), while emergence and tillering showed weak, non-significant positive responses. Based on these findings, we propose a phenophase-specific adaptation framework that emphasizes targeted irrigation at the booting stage, regionally tailored cultivar selection, and flexible sowing management. This study provides new insights into the biometeorological mechanisms linking drought and crop development and offers a transferable foundation for improving climate adaptation in winter wheat systems.