Spatiotemporal Evolution of Waterlogging Intensity During Winter Oilseed Rape Growth Stages and Its Relationship with Yield Losses in the Middle-Lower Yangtze River Region

Understanding the spatiotemporal evolution of waterlogging intensity across winter oilseed rape (WOSR) growth stages and its quantitative relationship with yield losses is critical for agricultural water management in the Middle-Lower Yangtze River Region (MLYRR). Here, a daily-scale agrometeorological index (SAPEI) was introduced to quantify waterlogging intensity during four WOSR growth stages from 1961 to 2020. Waterlogging intensity increased significantly over the past six decades in most areas, particularly during the overwintering stage (38 stations, 57% of all stations), with the 2000s representing the historical high levels for most provinces, followed by those in the 1990s. The northeastern and southernmost MLYRR were identified as highly waterlogging-prone regions, and the overwintering stage exhibited substantially larger daily waterlogging intensity than other stages. The yield-reducing impact of severe waterlogging (SAPEI > 1.0) was greater than general waterlogging (SAPEI > 0.5), with larger absolute regression coefficients of waterlogging indices. The flowering–maturing stage, followed by the overwintering stage, was the most waterlogging-sensitive period, and it was also selected as the sole explanatory variable in up to 14 districts in stepwise regression. A marked spatial mismatch was found between waterlogging proneness and crop sensitivity, suggesting that drainage scheduling should account for crop waterlogging sensitivity rather than waterlogging intensity alone. These findings provide guidance for targeted WOSR drainage planning in key regions of the MLYRR under climate change.