Cumulative? lagged? Quantification of the actual temporal effects of climate change on corn phenology in China’s major cultivation zones

Understanding the temporal effects of climatic conditions on crop phenology is crucial for climate change adaptation and food security. However, existing studies do not distinguish well between the effects of anthropogenic management practices (AMP) and climate factors, leaving the actual temporal effects of climate change on crop phenology unclear. Therefore, we designed an analytical framework for assessing the actual temporal effects of climate change on crop phenology, both cumulative and lagged. Specifically, the Hodrick-Prescott (HP) filter was applied to isolate the individual impacts of climate and AMP on phenology, and grey correlation analysis was utilized to quantify the temporal effects. The study area was the major corn cultivation zones in China, and spanned a three-decade period, from 1990 to 2020. Two key phenological periods during corn growth were emphasized, namely, the three-leaf stage (climate phenology V3C) and the maturity stage. Results showed that: (1) HP filters were shown to be effective in separating the effects of AMP. Without separation, there would have been a 25±10% underestimation of the effect of climate change on corn phenology; (2) The temporal effects of climate change on corn phenology are affected by AMP, with cumulative time generally lengthened by 3-29 days and lag time generally shortened by 2-11 days; (3) The lag effect is the dominant temporal effect of climate change affecting corn phenology within the major cultivation zones in China, and its intensity is higher than the cumulative intensity by “0.06±0.02”; (4) The temporal impacts of climate change on corn phenology vary significantly across space. The lag time of V3C response to temperature (Temp) and solar radiation (SSRnet) is longer than the cumulative time in the northwest arid zone, while the opposite is true in other northern zones. The “Qinling-Huaihe line” is the demarcation line for the temporal effects of Temp and SSRnet on corn phenology. North of this demarcation, the cumulative duration surpassed the lag duration, while to the south, the situation was inversely proportional.