Remote Sensing, Vol. 11, Pages 2976: Interactions among the Phenological Events of Winter Wheat in the North China Plain-Based on Field Data and Improved MODIS Estimation (Remote Sensing)

Identification of complete drivers for phenology changes is crucial for developingprediction models of plant phenology. In addition to climatic factors, the interaction amongphenological events has recently been reported as an important driver for the phenology changesof forests, savannas, and grasslands. However, open questions remain as to whether thephenological interaction exists in agricultural ecosystems, among which winter wheat plays a vitalrole in feeding human beings. In this study, we investigated the interaction among the phenologicalevents of winter wheat in the North China Plain (NCP) using both field and satellite data.Considering the large discrepancies between the existing satellite estimation and fieldmeasurements of winter wheat phenology, we first improved the MODIS-based estimation ofgreen-up date (GUD), heading date (HD), and maturity date (MD) through a re-calibrated relativethreshold method (RTM) in the NCP. The GUD, HD, and MD were accurately estimated with themean absolute errors (MAE) and root mean squared errors (RMSE) lower than 7.5 days, comparedwith the RMSEs ranging from 12.0 to 36.1 days in previous studies. Then, the relationships amongthe GUD, HD, and MD were analyzed using the field data collected at agricultural meteorologicalstations. The GUD (HD) showed a significantly positive correlation with the HD (MD).Quantitatively, a one-day earlier GUD (HD) would result in an earlier HD (MD) of 0.57 days (0.60days). Furthermore, we applied the partial correlation analysis to the improved MODIS estimationof GUD, HD, and MD to investigate their interactions by considering the simultaneous influencesfrom climatic factors. The results showed that the HD (MD) with 85.2% (94.5%) of all winter wheatpixels presented a significantly positive correlation with the GUD (HD). Meanwhile, the GUD (HD)with 84.2% (33.3%) of the entire winter wheat area presented a significantly negative correlationwith pre-season temperature. These results suggest that both the climatic factors and phenologicalinteractions should be included in the future development of winter wheat phenology models toimprove the prediction accuracies.